LT6658 Precision Dual Output, High Current, Low Noise, Voltage Reference. Applications. Typical Application

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1 Features Dua Output Tracking Reference Each Output Configurabe to 6 Output : ma Source/2mA Sink Output 2: ma Source/2mA Sink Low Drift: A-Grade: ppm/ C Max B-Grade: 2ppm/ C Max High Accuracy: A-Grade: ±.% Max B-Grade: ±.% Max Low Noise:.ppm P-P (.Hz to Hz) Wide Operating otage Range to 36 Load Reguation:.ppm/mA AC PSRR: 96dB at khz Kevin Sense Coection on Outputs Therma Shutdown Separate Suppy Pins for Each Output Avaiabe Output otage Options:.2,., 2., 3, 3.3,. A Options are Adjustabe Avaiabe in Exposed Pad Package MSE6 Appications Microcontroer or FPGA with ADC/DAC Appications Data Acquisition Systems Automotive Contro and Monitoring Precision Low Noise Reguators Instrumentation and Process Contro Typica Appication Precision Dua Output 2. Reference and Suppy LT66 Precision Dua Output, High Current, Low Noise, otage Reference Description The LT 66 is a famiy of precision dua output references combining the performance of a precision votage reference and a inear reguator that we ca the Refuator. Both outputs are idea for driving the reference inputs of high resoution ADCs and DACs, even with heavy oading, whie simutaneousy powering microcontroers and other circuitry. Both outputs have the same precision specifications and track each other over temperature and oad. Each output can be configured with externa resistors to give an output votage up to 6. Using Kevin coections, the LT66 typicay has.ppm/ma oad reguation with up to ma oad current. A noise reduction pin is avaiabe to band-imit and ower the tota integrated noise. Separate suppy pins are provided for each output, providing an option to reduce power consumption and isoate the buffer ampifiers. The outputs have exceent suppy rejection and are stabe with to µf capacitors. The LT66 is avaiabe in a 6-ead MSOP with an exposed pad for therma management. Short circuit and therma protection hep to prevent therma overstress. L, LT, LTC, LTM, Linear Technoogy and the Linear ogo are registered trademarks and Refuator and ThinSOT are trademarks of Anaog Devices, Inc. A other trademarks are the property of their respective owners. Output otage Temperature Drift Both Outputs 2.2 TO 36. OUT2_F 2 OUT2_S LT66-2. OD OUT_F BYPASS OUT_S R LOAD2 R LOAD OUT2 2. ma OUT 2. ma 66 TAa OUTPUT OLTAGE () I LOAD = ma OUT OUT TEMPERATURE ( C) 66 TAb

2 LT66 Absoute Maximum Ratings (Note ) Suppy otages,, 2 to....3 to 3 Input otages OD to....3 to 3 OUT_S, OUT2_S, NR, BYPASS to....3 to 6 Output otages OUT_F, OUT2_F to....3 to 6 Input Current BYPASS... ±ma Output Short-Circuit Duration... Indefinite Specified Temperature Range I-Grade... 4 C to C H-Grade... 4 C to Operating Junction Temperature Range.. C to C Storage Temperature Range (Note 2)... 6 C to C Lead Temperature (Sodering, sec) (Note 3)...3 C Pin Configuration BYPASS DNC NR OUT2_S OUT2_F TOP IEW DNC NC OUT_S OUT_F 2 OD MSE PACKAGE 6-LEAD PLASTIC MSOP T JMAX = C, θ JC = C/W, θ JA = 3 C/W DNC: CONNECTED INTERNALLY DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS EXPOSED PAD (PIN 7) IS, MUST BE SOLDERED TO PCB Order Information TUBE TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED JUNCTION TEMPERATURE RANGE LT66AIMSE-.2#PBF LT66AIMSE-.2#TRPBF Lead Pastic MSOP 4 C to C LT66BIMSE-.2#PBF LT66BIMSE-.2#TRPBF Lead Pastic MSOP 4 C to C LT66AHMSE-.2#PBF LT66AHMSE-.2#TRPBF Lead Pastic MSOP 4 C to LT66BHMSE-.2#PBF LT66BHMSE-.2#TRPBF Lead Pastic MSOP 4 C to LT66AIMSE-.#PBF LT66AIMSE-.#TRPBF 66 6-Lead Pastic MSOP 4 C to C LT66BIMSE-.#PBF LT66BIMSE-.#TRPBF 66 6-Lead Pastic MSOP 4 C to C LT66AHMSE-.#PBF LT66AHMSE-.#TRPBF 66 6-Lead Pastic MSOP 4 C to LT66BHMSE-.#PBF LT66BHMSE-.#TRPBF 66 6-Lead Pastic MSOP 4 C to LT66AIMSE-2.#PBF LT66AIMSE-2.#TRPBF Lead Pastic MSOP 4 C to C LT66BIMSE-2.#PBF LT66BIMSE-2.#TRPBF Lead Pastic MSOP 4 C to C LT66AHMSE-2.#PBF LT66AHMSE-2.#TRPBF Lead Pastic MSOP 4 C to LT66BHMSE-2.#PBF LT66BHMSE-2.#TRPBF Lead Pastic MSOP 4 C to LT66AIMSE-3#PBF LT66AIMSE-3#TRPBF Lead Pastic MSOP 4 C to C LT66BIMSE-3#PBF LT66BIMSE-3#TRPBF Lead Pastic MSOP 4 C to C LT66AHMSE-3#PBF LT66AHMSE-3#TRPBF Lead Pastic MSOP 4 C to LT66BHMSE-3#PBF LT66BHMSE-3#TRPBF Lead Pastic MSOP 4 C to LT66AIMSE-3.3#PBF LT66AIMSE-3.3#TRPBF Lead Pastic MSOP 4 C to C LT66BIMSE-3.3#PBF LT66BIMSE-3.3#TRPBF Lead Pastic MSOP 4 C to C 2

3 LT66 Order Information TUBE TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED JUNCTION TEMPERATURE RANGE LT66AHMSE-3.3#PBF LT66AHMSE-3.3#TRPBF Lead Pastic MSOP 4 C to LT66BHMSE-3.3#PBF LT66BHMSE-3.3#TRPBF Lead Pastic MSOP 4 C to LT66AIMSE-#PBF LT66AIMSE-#TRPBF 66 6-Lead Pastic MSOP 4 C to C LT66BIMSE-#PBF LT66BIMSE-#TRPBF 66 6-Lead Pastic MSOP 4 C to C LT66AHMSE-#PBF LT66AHMSE-#TRPBF 66 6-Lead Pastic MSOP 4 C to LT66BHMSE-#PBF LT66BHMSE-#TRPBF 66 6-Lead Pastic MSOP 4 C to *The temperature grade is identified by a abe on the shipping container. Consut LTC Marketing for parts specified with wider operating temperature ranges. Parts ending with PBF are RoHS and WEEE compiant. For more information on ead free part marking, go to: For more information on tape and ree specifications, go to: Avaiabe Options OUTPUT OLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT ORDER PART NUMBER ** SPECIFIED JUNCTION TEMPERATURE RANGE.2.% ppm/ C LT66AIMSE-.2 4 C to C.% 2ppm/ C LT66BIMSE-.2 4 C to C.% ppm/ C LT66AHMSE-.2 4 C to.% 2ppm/ C LT66BHMSE-.2 4 C to..% ppm/ C LT66AIMSE-. 4 C to C.% 2ppm/ C LT66BIMSE-. 4 C to C.% ppm/ C LT66AHMSE-. 4 C to.% 2ppm/ C LT66BHMSE-. 4 C to 2..% ppm/ C LT66AIMSE-2. 4 C to C.% 2ppm/ C LT66BIMSE-2. 4 C to C.% ppm/ C LT66AHMSE-2. 4 C to.% 2ppm/ C LT66BHMSE-2. 4 C to 3..% ppm/ C LT66AIMSE-3 4 C to C.% 2ppm/ C LT66BIMSE-3 4 C to C.% ppm/ C LT66AHMSE-3 4 C to.% 2ppm/ C LT66BHMSE-3 4 C to 3.3.% ppm/ C LT66AIMSE C to C.% 2ppm/ C LT66BIMSE C to C.% ppm/ C LT66AHMSE C to.% 2ppm/ C LT66BHMSE C to..% ppm/ C LT66AIMSE- 4 C to C.% 2ppm/ C LT66BIMSE- 4 C to C.% ppm/ C LT66AHMSE- 4 C to.% 2ppm/ C LT66BHMSE- 4 C to 3

4 LT66 Eectrica Characteristics The denotes the specifications which appy over the fu specified temperature range, otherwise specifications are at T A =. = = 2 = OUT,2_F + 2., C OUT,2 =.3µF, I LOAD =, uness otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Output otage Accuracy Output otage Temperature Coefficient (Note 4) Line Reguation (Note ) LT66A LT66B LT66AI LT66BI LT66AH LT66BH LT66A LT66B LT66-.2, LT , = = 2 LT66-2., LT66-3.3, LT66- OUT , = = 2 Load Reguation (Note ) Output Sourcing, ΔI LOAD = ma to ma Minimum otage Dropout otage 2 Dropout otage Output 2 Sourcing, ΔI LOAD = ma to ma (Note 6) Output Sinking, ΔI LOAD = ma to 2mA Output 2 Sinking, ΔI LOAD = ma to 2mA LT66-.2, LT66-., LT66-2. Δ OUT =.%, I OUT = ma, = 2 = 4. LT66-3 Δ OUT =.%, I OUT = ma, = 2 =. LT Δ OUT =.%, I OUT = ma, = 2 =. LT66- Δ OUT =.%, I OUT = ma, = 2 = 7. LT66-.2, LT66-. Δ OUT =.%, I OUT = ma, = 2 = OUT + 4. Δ OUT =.%, I OUT = ma, = 2 = OUT + 4. LT66-2., LT66-3, LT66-3.3, LT66- Δ OUT =.%, I OUT = ma, = 2 = OUT + 2. Δ OUT =.%, I OUT = ma, = 2 = OUT + 2. LT66-.2, LT66-. Δ OUT2 =.%, I OUT2 = ma, = = OUT + 4. Δ OUT2 =.%, I OUT2 = ma, = = OUT + 4. LT66-2., LT66-3, LT66-3.3, LT66- Δ OUT2 =.%, I OUT2 = ma, = = OUT + 2. Δ OUT2 =.%, I OUT2 = ma, = = OUT % % % % % % ppm/ C ppm/ C ppm/ ppm/ ppm/ ppm/ µ/ma µ/ma µ/ma µ/ma µ/ma µ/ma µ/ma µ/ma Suppy Current LT66-.2, OD = 2., No Load ma LT66-., OD = 2., No Load ma LT66-2., LT66-3, LT66-3.3, LT66-, OD = 2., No Load.9 3. ma OD =., No Load LT66-.2 LT66-. LT66-2. LT66-3 LT LT ma ma ma ma ma ma 4

5 LT66 Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A =. = = 2 = OUT,2_F + 2., C OUT,2 =.3µF, I LOAD =, uness otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Output Short-Circuit Current Short OUT_F to Short OUT2_F to ma ma Output Noise otage (Note 7).Hz f Hz LT66-.2 LT66-. LT66-2. LT66-3 LT LT66- Hz f khz, C OUT =, C NR =, I LOAD = Fu Current (Note 9) Hz f khz, C OUT =, C NR = OPEN, I LOAD = Fu Current (Note 9) Frequency = khz, C OUT =, C NR =, I LOAD = Fu Current (Note 9) ppm P P ppm P P ppm P P ppm P P ppm P P ppm P P ppm RMS ppm RMS n/ Hz Output otage Tracking Tracking = Output Output 2.9 µ/ C OUT_S, OUT2_S Pin Current Unity Gain 3 na OD Threshod otage Logic High Input otage 2 Logic Low Input otage. OD Pin Current OD = OD = μa μa Rippe Rejection = OUT + 3, RIPPLE =. P P, f RIPPLE = 2Hz, I LOAD = ma, C OUT =, C NR = 2 = OUT2 + 3, RIPPLE =. P P, f RIPPLE = 2Hz, I LOAD = ma, 7 7 db db C OUT2 =, C NR = Turn-On Time.% Setting, C LOAD = μf 6 μs Long Term Drift (Note ) 2 ppm/ khr Therma Hysteresis (Note 9) T = 4 C to C T = 4 C to 3 4 ppm ppm Note : Stresses beyond those isted under Absoute Maximum Ratings may cause permanent damage to the device. Exposure to any Absoute Maximum Rating condition for extended periods may affect device reiabiity and ifetime. Note 2: Therma hysteresis can occur during storage at extreme temperatures. Note 3: The stated temperature is typica for sodering of the eads during manua rework. For detaied IR refow recommendations, refer to the Appications Information section. Note 4: Temperature coefficient is measured by dividing the maximum change in output votage by the specified temperature range. Note : Line and oad reguation are measured on a puse basis for specified input votage or oad current ranges. Output changes due to die temperature change must be taken into account separatey. Note 6: OUT2 oad reguation specification is imited by practica automated test resoution. Pease refer to the Typica Performance Characteristics section for more information regarding actua typica performance. Note 7: Peak-to-peak noise is measured with a -poe highpass fiter at.hz and 2-poe owpass fiter at Hz. The unit is encosed in a sti-air environment to eiminate thermocoupe effects on the eads. The test time is seconds. RMS noise is measured on a spectrum anayzer in a shieded environment where the intrinsic noise of the instrument is removed to determine the actua noise of the device. Note : Long-term stabiity typicay has a ogarithmic characteristic and therefore, changes after hours tend to be much smaer than before that time. Tota drift in the second thousand hours is normay ess than one third that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stabiity wi aso be affected by differentia stresses between the IC and the board materia created during board assemby. Note 9: Hysteresis in output votage is created by package stress that differs depending on whether the IC was previousy at a higher or ower temperature. Output votage is aways measured at, but the IC is cyced to the hot or cod temperature imit before successive measurements. Hysteresis measures the maximum output change for the averages of three hot or cod temperature cyces. For instruments that are stored at we controed temperatures (within 2 or 3 degrees of operationa temperature), it s usuay not a dominant error source. Typica hysteresis is the worst-case of to cod to or to hot to, preconditioned by one therma cyce. Note : The fu current for I LOAD is ma and ma for Output and Output 2, respectivey.

6 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output OUT Output otage Temperature Drift THREE TYPICAL PARTS.22.2 OUT2 Output otage Temperature Drift THREE TYPICAL PARTS.22.2 OUT and OUT2 Output otage vs Temperature with ma Load on OUT I LOAD = ma OUTPUT OLTAGE () OUTPUT OLTAGE CHANGE (ppm) TEMPERATURE ( C) OUT Load Reguation, Sourcing 4 C 66 G. OUTPUT CURRENT (ma) 66 G4 OUTPUT OLTAGE () OUTPUT OLTAGE CHANGE (ppm) TEMPERATURE ( C) OUT2 Load Reguation, Sourcing 4 C 66 G2. OUTPUT CURRENT (ma) 66 G OUTPUT OLTAGE () OUTPUT OLTAGE CHANGE (ppm) TEMPERATURE ( C).2 OUT Load Reguation, Sinking 4 C OUT OUT2 66 G3. OUTPUT CURRENT (ma) 66 G6.2 OUT2 Load Reguation, Sinking.2 Line Reguation OUT.2 Line Reguation OUT OUTPUT OLTAGE CHANGE (ppm) C. OUTPUT CURRENT (ma) 66 G7 OUTPUT OLTAGE () C INPUT OLTAGE () 66 G OUTPUT OLTAGE () C INPUT OLTAGE () 66 G9

7 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output Suppy Current vs Input otage 2.2 OUT Power Suppy Rejection Ratio vs Frequency = = 2 = C OUT = I LOAD = A 2.2 OUT2 Power Suppy Rejection Ratio vs Frequency = = 2 = C OUT2 = I LOAD = A INPUT CURRENT (ma) PSRR (db) OUT Power Suppy Rejection Ratio vs Frequency 4 C INPUT OLTAGE () 66 G = = 2 = C NR = C OUT = 2 I LOAD = ma I LOAD = ma.. 66 G3 PSRR (db) PSRR (db) C NR = C NR = OUT2 Power Suppy Rejection Ratio vs Frequency 66 G = = 2 = C NR = C OUT2 = 2 I LOAD = ma I LOAD = ma.. 66 G4 PSRR (db) OUTPUT IMPEDANCE (Ω) C NR = C NR = G2.2 OUT AC Output Impedance ma Load I OUT = ma C OUT = C OUT = µf.. 66 G.2 OUT AC Output Impedance ma Load I OUT = ma.2 OUT2 AC Output Impedance ma Load I OUT = ma.2 OUT2 AC Output Impedance ma Load I OUT = ma OUTPUT IMPEDANCE (Ω)... OUTPUT IMPEDANCE (Ω)... OUTPUT IMPEDANCE (Ω).... C OUT = C OUT = µf.. 66 G6. C OUT2 = C OUT2 = µf.. 66 G7. C OUT2 = C OUT2 = µf.. 66 G 7

8 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output..2 Turn-On Characteristic.2 Chae to Chae Load Isoation OUT2 to OUT.2 Chae to Chae Load Isoation OUT to OUT2 /DI 2/DI 2/DI 2/DI BYPASS OUT OUT2 µs/di C NR = OPEN C OUT = C OUT2 = 66 G9 OUT CHANNEL TO CHANNEL ISOLATION (db) m RMS SIGNAL ON OUT2 2 I LOAD2 = ma I LOAD2 = ma.. 66 G2 OUT2 CHANNEL TO CHANNEL ISOLATION (db) m RMS SIGNAL ON OUT 2 I LOAD = ma I LOAD = ma.. 66 G2.2 OUT Output Noise.Hz to Hz.2 OUT2 Output Noise.Hz to Hz 2.2 OUT Output otage Noise Spectrum I LOAD = ma C OUT = 2 µ/di s/di 66 G22 µ/di s/di 66 G23 NOISE OLTAGE (n/ Hz) C NR = OPEN C NR =.. 66 G OUT2 Output otage Noise Spectrum I LOAD = ma.2 Line Transient Response.2 Line Transient Response C OUT2 = m/di m/di NOISE OLTAGE (n/ Hz) 2 C NR = OPEN C NR =.. 66 G2 2m/DI 2m/DI 2m/DI BYPASS OUT OUT2 C NR = OPEN C OUT = C OUT2 = µs/di = 4. TO I LOAD = ma 66 G26 2m/DI 2m/DI 2m/DI BYPASS OUT OUT2 C NR = C OUT = C OUT2 = µs/di = 4. to I LOAD = ma 66 G27

9 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. m/di 2m/DI 2m/DI 2m/DI Line Transient Response.2 OUT Current Limit.2 OUT2 Current Limit BYPASS OUT OUT2 C NR = C OUT = C OUT2 = µs/di 2. OUT Output otage Temperature Drift THREE TYPICAL PARTS = 4. TO I LOAD = ma 66 G2 CURRENT LIMIT (ma) = = TEMPERATURE ( C) OUT2 Output otage Temperature Drift THREE TYPICAL PARTS 66 G29 CURRENT LIMIT (ma) = = TEMPERATURE ( C) OUT and OUT2 Output otage vs Temperature with ma Load on OUT I LOAD = ma 66 G3 OUTPUT OLTAGE () TEMPERATURE ( C) 66 G3 OUTPUT OLTAGE () TEMPERATURE ( C) 66 G32 OUTPUT OLTAGE () OUT OUT TEMPERATURE ( C) 66 G33 OUTPUT OLTAGE CHANGE (ppm) OUT Load Reguation, Sourcing 4 C OUTPUT CURRENT (ma) 66 G34 OUTPUT OLTAGE CHANGE (ppm) 2 2. OUT2 Load Reguation, Sourcing 4 C LOAD CURRENT (ma) 66 G3 OUTPUT OLTAGE CHANGE (ppm) 2. OUT Load Reguation, Sinking 4 C OUTPUT CURRENT (ma) 66 G36 9

10 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. OUTPUT OLTAGE CHANGE (ppm) 2. OUT2 Load Reguation, Sinking 2. Line Reguation OUT 2. Line Reguation OUT2 4 C OUTPUT CURRENT (ma) 66 G37 OUTPUT OLTAGE () C INPUT OLTAGE () 66 G3 OUTPUT OLTAGE () C INPUT OLTAGE () 66 G39 NUMBER OF UNITS OUT () 2 2. Output Accuracy Histogram 2. Minimum to OUT Differentia, Sourcing 66 G4 SUPPLY CURRENT (ma) Suppy Current vs Input otage 4 C INPUT OLTAGE () 2. Minimum to OUT2 Differentia, Sourcing 66 G4 SUPPLY CURRENT (ma) Output Disabe (OD) Low Suppy Current vs Input otage 4 C INPUT OLTAGE () 2. OUT Power Suppy Rejection Ratio vs Frequency 66 G42 = = 2 = 6 OUTPUT CURRENT (ma). 4 C INPUT OUTPUT OLTAGE () 66 G43 OUTPUT CURRENT (ma). 4 C INPUT OUTPUT OLTAGE () 66 G44 PSRR (db) 6 4 C OUT = I LOAD = A 2 C NR = C NR =.. 66 G4

11 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output OUT2 Power Suppy Rejection Ratio vs Frequency = = 2 = OUT Power Suppy Rejection Ratio vs Frequency = = 2 = OUT2 Power Suppy Rejection Ratio vs Frequency = = 2 = 6 PSRR (db) 6 PSRR (db) 6 PSRR (db) 6 4 C OUT2 = 2 I LOAD = A C NR = C NR =.. 66 G C NR = C OUT = I LOAD = A I LOAD = ma.. 66 G C NR = C OUT = I LOAD = A I LOAD = ma.. 66 G4 2. OUT AC Output Impedance ma Load 2. OUT AC Output Impedance ma Load 2. OUT2 AC Output Impedance ma Load OUTPUT IMPEDANCE (Ω).... I OUT = ma C OUT = C OUT = µf.. 66 G49 OUTPUT IMPEDANCE (Ω).... I OUT = ma C OUT = C OUT = µf.. 66 G OUTPUT IMPEDANCE (Ω).... I OUT2 = ma C OUT2 = C OUT2 = µf.. 66 G 2. OUT2 AC Output Impedance ma Load 2. Turn-On Characteristic /DI OUTPUT IMPEDANCE (Ω)... I OUT2 = ma C OUT2 = C OUT2 = µf G2 2/DI 2/DI 2/DI BYPASS OUT OUT2 µs/di C NR = OPEN C OUT = C OUT2 = 66 G3

12 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. OUT2 CHANNEL TO CHANNEL ISOLATION (db) OUT2 CHANNEL TO CHANNEL ISOLATION (db) m RMS SIGNAL ON OUT 2 I LOAD = ma I LOAD = ma Chae to Chae Load Isoation OUT to OUT2 2. Chae to Chae Isoation to OUT2 C OUT2 = µf / C NR = C OUT2 = / C NR = OPEN 66 G4 C OUT2 = / C NR = 2 = 2 = 7 = 6DC + 7m RMS I LOAD = I LOAD2 = A, T A =.. 66 G7 OUT CHANNEL TO CHANNEL ISOLATION (db) OUT2 OLTAGE CHANGE (ppm) m RMS SIGNAL ON OUT2 2 I LOAD2 = ma I LOAD2 = ma Chae to Chae Load Isoation OUT2 to OUT 2. Chae to Chae Load Reguation (Effects of Heating Removed) 66 G OUT LOAD CURRENT (ma) 66 G OUT CHANNEL TO CHANNEL ISOLATION (db) ma C OUT = / C NR = OPEN C OUT = µf / C NR = C OUT = / C NR = 4 = = = 6DC + 7m RMS I LOAD = I LOAD2 = A, T A =.. ma µ/di 2. Chae to Chae Isoation 2 to OUT 2. Chae to Chae Isoation, Time Domain I OUT OUT2 C NR =. C OUT = C OUT2 = µs/di 66 G6 66 G9 OUT_S PIN CURRENT (na) OUT_S Pin Input Current vs Temperature THREE TYPICAL PARTS TEMPERATURE ( C) 66 G6 OD PIN INPUT CURRENT (µa). 2. OD Pin Current vs OD Pin Input otage 4 C OD PIN INPUT OLTAGE () 66 G6 OUT - OUT2 (µ) Tracking ( OUT OUT2 ) vs Temperature THREE TYPICAL PARTS TEMPERATURE ( C) 66 G62

13 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output Tracking ( OUT OUT2 ) vs Input otage THREE TYPICAL PARTS Tracking ( OUT OUT2 ) vs OUT Load Current THREE TYPICAL PARTS 2. OUT Output Noise.Hz to Hz 9 2 OUT OUT2 (µ) OUT OUT2 (µ) 4 4 OUTPUT NOISE (2µ/DI) s/di 66 G () 66 G k OUT LOAD CURRENT (ma) 66 G64 2. OUT2 Output Noise.Hz to Hz 3 2. OUT Output otage Noise Spectrum I LOAD = ma C OUT = 3 2. OUT2 Output otage Noise Spectrum I LOAD = ma C OUT2 = OUTPUT NOISE (2µ/DI) s/di 66 G66 NOISE OLTAGE (n/ Hz) C NR = OPEN C NR = NOISE OLTAGE (n/ Hz) C NR = OPEN C NR = NOISE OLTAGE (n/ Hz) OUT Output otage Noise Spectrum I LOAD = ma C OUT = C NR = OPEN C NR =.. 66 G69 NOISE OLTAGE (n/ Hz) C OUT2 = C NR = OPEN C NR = 66 G67 2. OUT2 Output otage Noise Spectrum I LOAD = ma.. 66 G7.. INTEGRATED NOISE (µ RMS ) OUT Integrated Noise I LOAD = ma C NR = PEN C NR = C OUT = I LOAD = ma 66 G G7 3

14 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. INTEGRATED NOISE (µ RMS ) OUT2 Integrated Noise I LOAD = ma C NR = OPEN C NR = C OUT2 = I LOAD = ma.. 66 G72 INTEGRATED NOISE (µ RMS ) OUT Integrated Noise I LOAD = ma C NR = OPEN C NR = C OUT = I LOAD = ma.. 66 G73 INTEGRATED NOISE (µ RMS ) OUT2 Integrated Noise I LOAD = ma C NR = OPEN C NR = C OUT2 = I LOAD = ma.. 66 G74 2. Line Transient Response 2. Line Transient Response 2. Line Transient Response m/di m/di m/di 2m/DI 2m/DI 2m/DI BYPASS OUT OUT2 C NR = OPEN C OUT = C OUT2 = = to. I LOAD = ma 2m/DI 2m/DI 2m/DI BYPASS OUT OUT2 C NR = C OUT = C OUT2 = = to. I LOAD = ma 2m/DI 2m/DI 2m/DI BYPASS OUT OUT2 C NR = C OUT = C OUT2 = = to. I LOAD = ma µs/di 66 G7 µs/di 66 G76 µs/di 66 G77 CURRENT LIMIT (ma) OUT Current Limit 2. OUT2 Current Limit Current Limit vs Suppy otage = = 7. = TEMPERATURE ( C) 66 G7 CURRENT LIMIT (ma) = = TEMPERATURE ( C) 66 G79 CURRENT LIMIT (ma) I OUT I OUT SUPPLY OLTAGE () 66 G 4

15 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output..6 OUT Output otage Temperature Drift THREE TYPICAL PARTS.6 OUT2 Output otage Temperature Drift THREE TYPICAL PARTS.6 OUT and OUT2 Output otage vs Temperature with ma Load on OUT I LOAD = ma OUTPUT OLTAGE () OUTPUT OLTAGE () OUTPUT OLTAGE () TEMPERATURE ( C) 66 G TEMPERATURE ( C) 66 G OUT OUT TEMPERATURE ( C) 66 G3 OUTPUT OLTAGE CHANGE (ppm) OUT Load Reguation, Sourcing 4 C. OUTPUT CURRENT (ma) 66 G4 OUTPUT OLTAGE CHANGE (ppm) 2 OUT2 Load Reguation, Sourcing 4 C 2. OUTPUT CURRENT (ma) 66 G OUTPUT OLTAGE CHANGE (ppm) OUT Load Reguation, Sinking 4 C. OUTPUT CURRENT (ma) 66 G6 OUTPUT OLTAGE CHANGE (ppm) OUT2 Load Reguation, Sinking Line Reguation OUT Line Reguation OUT2 4 C OUTPUT OLTAGE () C OUTPUT OLTAGE () C 2. OUTPUT CURRENT (ma) 66 G INPUT OLTAGE () 66 G INPUT OLTAGE () 66 G9

16 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. 2. Suppy Current vs Input otage 2 Minimum to OUT Differentia (Sourcing) Minimum to OUT2 Differentia (Sourcing) 2. INPUT CURRENT (ma)... 4 C INPUT OLTAGE () 66 G9 OUTPUT CURRENT (A). = = 2 4 C INPUT OUTPUT OLTAGE () 66 G9 OUTPUT CURRENT (ma). = = 2 4 C INPUT OUTPUT OLTAGE () 66 G92 2 OUT Power Suppy Rejection Ratio vs Frequency C OUT = I LOAD = A 2 OUT2 Power Suppy Rejection Ratio vs Frequency C OUT2 = I LOAD2 = A 2 OUT Power Suppy Rejection Ratio vs Frequency C NR = C OUT = PSRR (db) 6 PSRR (db) 6 PSRR (db) C NR = C NR =.. 66 G93 2 C NR = C NR =.. 66 G94 2 I LOAD = A I LOAD = ma.. 66 G9 PSRR (db) OUT2 Power Suppy Rejection Ratio vs Frequency C NR = C OUT2 = 2 I LOAD2 = A I LOAD2 = ma.. 66 G96 OUTPUT IMPEDANCE (Ω).... OUT AC Output Impedance ma Load I OUT = ma C OUT = C OUT = µf.. 66 G97 OUTPUT IMPEDANCE (Ω).... OUT AC Output Impedance ma Load I OUT = ma C OUT = C OUT = µf.. 66 G9

17 Typica Performance Characteristics LT66 T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. OUT2 AC Output Impedance ma Load I OUT2 = ma OUT2 AC Output Impedance ma Load I OUT2 = ma /DI Turn-On Characteristic OUTPUT IMPEDANCE (Ω).... C OUT2 = C OUT2 = µf.. 66 G99 OUTPUT IMPEDANCE (Ω).... C OUT2 = C OUT2 = µf.. 66 G /DI /DI /DI BYPASS OUT OUT2 µs/di C NR = OPEN C OUT = C OUT2 = 66 G Chae to Chae Load Isoation OUT2 to OUT Chae to Chae Load Isoation OUT to OUT2 OUT CHANNEL TO CHANNEL ISOLATION (db) m RMS SIGNAL ON OUT2 2 I LOAD2 = ma I LOAD2 = A.. 66 G2 OUT2 CHANNEL TO CHANNEL ISOLATION (db) m RMS SIGNAL ON OUT 2 I LOAD2 = ma I LOAD2 = A.. 66 G3 OUT Output Noise.Hz to Hz OUT2 Output Noise.Hz to Hz OUTPUT NOISE 2µ/DI OUTPUT NOISE 2µ/DI s/di 66 G4 s/di 66 G 7

18 LT66 Typica Performance Characteristics T A =, = = 2 = OUT_F + 2. = OUT2_F + 2. except LT66-.2 where = = 2 = 4., C OUT = C OUT2 =, I LOAD = ma, uness otherwise noted. The characteristic curves are simiar across the LT66 famiy. Curves from the LT66-.2, LT66-2. and the LT66- represent the fu range of typica performance of a votage options. Characteristic curves for other output votages fa between these curves and can be estimated based on their output. 7 6 OUT Output otage Noise Spectrum I LOAD = ma C OUT = 7 6 OUT2 Output otage Noise Spectrum I LOAD = ma C OUT2 = NOISE OLTAGE (n/ Hz) C NR = OPEN NOISE OLTAGE (n/ Hz) C NR = OPEN C NR =.. 66 G6 C NR =.. 66 G7 Line Transient Response Line Transient Response m/di m/di 2m/DI BYPASS 2m/DI BYPASS 2m/DI 2m/DI OUT OUT2 m/di m/di OUT OUT2 C NR = OPEN C OUT = C OUT2 = = 7. TO I LOAD = ma C NR = C OUT = C OUT2 = = 7. TO I LOAD = ma µs/di 66 G µs/di 66 G9 m/di 2m/DI m/di m/di Line Transient Response BYPASS OUT OUT2 C NR = C OUT = C OUT2 = µs/di = 7. TO I LOAD = ma 66 G CURRENT LIMIT (ma) OUT and OUT2 Current Limit = 7. 2 I OUT I OUT TEMPERATURE ( C) 66 G

19 Pin Functions (Pins, 2, 6, Exposed Pad Pin 7): These pins are the main ground coections and shoud be coected into a star ground or ground pane. The exposed pad must be sodered to ground for good eectrica contact and rated therma performance. BYPASS (Pin 3): Bypass Pin. This requires a μf capacitor for bandgap stabiity. DNC (Pin 4, 6): Do Not Coect. Keep eakage current from these pins to a minimum. NR (Pin ): Noise Reduction Pin. To band imit the noise of the reference, coect a capacitor between this pin and ground. See Appications Information section. OUT2_S (Pin 7): OUT2 Kevin Sense Pin. Coect this pin directy to the oad. OUT2_F (Pin ): OUT2 Output otage. A μf to μf output capacitor is required for stabe operation. This output can source up to ma. LT66 OD (Pin 9): Output Disabe. This active ow input disabes both outputs. 2 (Pin ): Input otage Suppy for Buffer 2. Bypass 2 with.μf capacitor to ground. This pin suppies power to buffer ampifier 2. (Pin ): Input otage Suppy for Buffer. Bypass with.μf capacitor to ground. This pin suppies power to buffer ampifier. OUT_F (Pin 2): OUT Output otage. A μf to μf output capacitor is required for stabe operation. This output can source up to ma. OUT_S (Pin 3): OUT Kevin Sense Pin. Coect this sense pin directy to the oad. (Pin 4): Input otage Suppy. Bypass with.μf capacitor to ground. NC (Pin ): No Coect. 9

20 LT66 Bock Diagram 4 9 OD DNC DNC BUFFER 2 OUT2_F NC THERMAL SHUTDOWN R4 OUT2_S 7 2 BANDGAP R R2 BUFFER OUT_F R3 OUT_S 3 BYPASS 3 NR 66 BD otage Option () R (Ω) R2 (Ω) R3, R4 (Ω) OPEN 3 4 OPEN OPEN 4 OPEN 2

21 Appications Information The LT66 combines the ow noise and accuracy of a high performance votage reference and the high current drive of a reguator. The LT66 Refuator provides two precise ow noise outputs with Kevin sense pins that maintain their precision even when arge votage or current transients exist on the adjacent buffer. The LT66 architecture consists of a ow drift bandgap reference foowed by an optiona noise reduction stage and two independent buffers. The bandgap reference and the buffers are trimmed for ow drift and high accuracy. The high gain buffers ensure outstanding ine and oad reguation. The guidance that foows describes how to reduce noise, ower power consumption, generate different output votages, and maintain ow drift. Aso incuded are notes on interna protection circuits, PCB ayout, and expected performance. Suppy Pins and Ground The LT66 can operate with a suppy votage from OUT + 2., to 36. To provide design fexibiity, the LT66 incudes 3 suppy pins. The pin suppies power to the bandgap votage reference. The and 2 pins suppy power to buffer ampifiers and 2, respectivey. Figure iustrates how current fows independenty through each of the output buffers. The simpest configuration is to coect a three suppy pins together. To reduce power consumption or isoate the buffer ampifiers, separate the suppy pins and drive them with independent suppies. Separate, and 2 suppy pins isoate the bandgap reference and the two outputs OUT_F and OUT2_F from each other. For exampe, a oad current surge through to OUT_F is isoated from OUT2_F and the bandgap votage reference. In Figure 2, a 4mA oad current puse on Buffer and the resuting output waveforms are shown. Despite the arge current step on Buffer, there is ony a sma transient at the output of Buffer 2. This isoation of two buffer outputs is important when providing a stabe votage reference to noise-sensitive circuits such as an ADC or DAC. In addition, power can be minimized by providing each suppy pin with its minimum votage. For exampe, if LT66 Buffer has a 2. output, can be operated at. If Buffer 2 s output is run at 3, run 2 at.. The power savings gained by minimizing each suppy votage can be considerabe. Excessive ground current and parasitic resistance in ground ines can degrade oad reguation. Unike an LDO, the ground of the LT66 is designed such that ground current does not increase substantiay when sourcing a arge oad current. A three ground pins and exposed pad shoud be coected together on the PCB, through a ground pane or through a separate trace terminating at a star ground. The suppy pins can be powered up in any order without an adverse response. However, a three pins need the minimum specified votage for proper operation LT66-2. BANDGAP THERMAL SHUTDOWN + +,2 7 6 INDICATES CURRENT FLOW OUT2_F OUT_F 2 LOAD2 LOAD Figure. LT66 Current Fow through the Suppy Pins ma/di 2m/DI µ/di LOAD CURRENT OUT OUT2 µs/di C OUT = C OUT2 = 66 F2 Figure 2. ma to ma Load Step on OUT 66 F 2

22 LT66 Appications Information Input Bypass Capacitance Each input votage pin requires a. capacitor ocated as cose to the suppy pin as possibe. A capacitor is recommended for each suppy where the suppy enters the board. When the suppy pins are coected together, a singe. and singe capacitor can be used. The BYPASS pin requires a capacitor for stabiity. Using the BYPASS Pin as a Reference The BYPASS pin requires a μf capacitor for stabiity and provides a bandgap votage to the output buffers. The bock diagram incudes a votage divider comprised of R and R2. R2 is open on the four votage options 2., 3, 3.3 and. Two votage options,.2 and., incude resistor R2 creating a votage divider. The votage at the BYPASS pin for these two options is different than the specified output votage. The tabe beow summarizes the BYPASS pin votage with respect to the output votage. Care shoud be exercised in choosing an output capacitor, as some capacitors tend to deviate from their specified vaue as operating conditions change. Athough ceramic capacitors are sma and inexpensive, they can vary consideraby over the DC bias votage. For exampe, the capacitance vaue of XR and X7R capacitors wi change significanty over their rated votage range as shown in Figure 3. In this exampe the XR capacitor oses amost 7% of its vaue at its rated votage of. CAPACITANCE (µf) XR X7R Tabe. BYPASS Pin otage otage Option () BYPASS Pin otage () The BYPASS pin can be used as an additiona votage reference pin. It nominay can source and sink ma. Note that any oading effect on the BYPASS pin gets passed to the output buffers. That is, if the BYPASS pin is pued down by m, the output pins wi respond simiary. Stabiity and Output Capacitance The LT66 is designed to be stabe for any output capacitance between and µf, under any oad condition, specified input votage, or specified temperature. Choosing a suitabe capacitor is important in maintaining stabiity. Preferaby a ow ESR and ESL capacitor shoud be chosen. The vaue of the output capacitor wi affect the setting response DC BIAS () 66 F3 Figure 3. Capacitance aue of a X7R and XR Over Its Fu Rated otage XR and X7R capacitors wi aso vary up to 2% or more over a temperature range of C to. This change in capacitance wi be combined with any DC bias votage variation. Fim capacitors do not vary much over temperature and DC bias as much as XR and X7R capacitors, but generay they are ony rated to C. Fim capacitors are aso physicay arger. Effective series resistance (ESR) in the output capacitor can add a zero to the oop response of the output buffers creating an instabiity or excessive ringing. For the best resuts keep the ESR at or beow.ω. One measure of stabiity is the cosed oop response of the output buffer. By driving the NR pin, a cosed oop response can be obtained. In Figure 4 the cosed oop response of the output buffer with three different output capacitance vaues is shown. In the Figure the same pot is repeated with a ma oad.

23 Appications Information A arge vaue eectroytic capacitor with a to µf ceramic capacitor in parae can be used on the output pins. The buffers wi be stabe, and the bandwidth wi be ower. 2 C OUT = LT66 the BYPASS and OUT_F pins for three different output capacitor vaues. The start-up response is imited by the current imit in the bandgap charging the BYPASS capacitor. The turn-on time is aso restricted by the current imit in the output buffer and the size of the output capacitor. A arger output capacitor wi take onger to charge. Adding a capacitor to the NR pin wi aso affect turn-on time. GAIN (db) C OUT = µf C OUT = 2.. k 66 F4 /DI 2/DI 2/DI 2/DI 2/DI OUT OUT OUT BYPASS µs/di C OUT = C OUT = C OUT = µf 66 F6 Figure 4. LT66 Cosed Loop Response of Buffer for 3 aues of Output Capacitance and No Load GAIN (db) 2 C OUT = µf C OUT = C OUT = 2.. k 66 F Figure. LT66 Cosed Loop Response of Buffer for 3 aues of Output Capacitance and ma Load Buffer 2 has a simiar response. Start-Up and Transient Response When the LT66 is powered up, the bandgap reference charges the capacitor on the BYPASS pin. The output buffer foows the votage on the BYPASS pin charging the output capacitor. Figure 6 shows the start-up response on Figure 6. Start-Up Response on the BYPASS and OUT_F Pins The test circuit for the transient response test is shown in Figure 7. The transient response due to oad current steps are shown in Figures, 9, and OD 3 BYPASS LT66-2. OUT2_F OUT2_S OUT_F OUT_S, 2, 6, 7 Ω 66 F7 Figure 7. Load Current Response Time Test Circuit In Figure and Figure 9, a 7mA and 4mA oad step is appied to Buffer, respectivey. In Figure, a 4mA oad step is appied to Buffer 2. The setting time is determined by the size and edge rate of the oad step, and the size of the output capacitor I GEN 23

24 LT66 Appications Information ma ma 2m/DI µ/di I OUT OUT OUT2 C NR =. C OUT = C OUT2 = µs/di 66 F Figure. LT66-2. Buffer Response to 7mA Load Step ma ma 2m/DI µ/di I OUT OUT OUT2 C NR =. C OUT = C OUT2 = µs/di 66 F9 Figure 9. LT66-2. Buffer Response to 4mA Load Step ma ma I OUT2 output votages. Unity gain is configured by tying the sense and force pins together. Figure provides an exampe where Buffer 2 is configured with a gain of 2. More exampes are provided in the Typica Appications section. When configuring a gain >, it's important to keep in mind that each output can ony swing to within 2. of its associated suppy votage, as specified in the dropout votage. Aso note that the absoute maximum votage on the output pins (both force and sense) is 6. Pace the feedback resistors cose to the part keeping the traces short. Avoid parasitic resistance in the high current path from the feedback resistor to ground. If possibe, the resistor to ground shoud be coected as cose as possibe to the chip ground. When using non-unity gain configurations, OS drift errors are possibe. There is an Ω resistor in the Kevin sense ine which is designed to cance base current variation on the input of the buffer ampifier. Matching the impedances on the positive and negative inputs reduces base current error and minimizes OS drift. A feedback network wi have a sma base current fowing through the feedback resistor possiby causing a sma OS drift. Referring to the 2. OUT_S Pin Input Current vs Temperature pot in the Typica Performance Characteristics section, the input sense current varies about na between 4 C and. This na variation may cause a.m votage change across the kω feedback resistor affecting the output votage. m/di OUT2 4 µ/di OUT C NR =. C OUT = C OUT2 = µs/di 66 F Figure. LT66-2. Output 2 Response to 4mA Load Step + BANDGAP LT66-2. THERMAL SHUTDOWN OUT2_F OUT2_S 7 OUT_F 2 OUT_S 3 k k Output otage Scaing The output buffers can be independenty configured with externa resistors to add gain, permitting non-standard, F Figure. The LT66-2. with Output 2 Configured for a Output 24

25 Appications Information Kevin Sense Pins To ensure the LT66 maintains good oad reguation, the Kevin sense pins shoud be coected cose to the oad to avoid any votage drop in the copper trace on the force pin. It ony takes mω of resistance to deveop a.m drop with ma. This woud cause an idea 2. output votage to exceed the.% specification at the oad. The circuit in Figure 2a iustrates how an incorrect Kevin sense coection can ead to errors. The parasitic resistance of the copper trace wi cause the output votage to change as the oad current changes. As a resut, the votage at the oad wi be ower than the votage at the sense ine. The circuit in Figure 2b shows the proper way to make a Kevin coection with the sense ine as cose to the oad as possibe. The votage at the oad wi now be we reguated. The OUT_S current is typicay 3nA, and a ow resistance in series with the Kevin sense input is unikey to cause a significant error or drift. + + LT66-2. OUT_F OUT_S LT66-2. OUT_F OUT_S a) b) PAR + R PAR PAR + R PAR *RPAR IS THE PARASITIC RESISTANCE I LOAD R LOAD I LOAD R LOAD 66 F2 Figure 2. How to Make a Proper Kevin Sense Coection Output Noise and Noise Reduction (NR) The LT66 noise characteristic is simiar to that of a high performance reference. The tota noise is a combination of the bandgap noise and the noise of the buffer ampifier. The bandgap noise can be measured at the NR pin and is shown in Figure 3 with a μf capacitor, LT66 capacitor and no capacitor on the NR pin. The bandgap can be bandimited by coecting a capacitor between the NR pin and ground. The RC product sets the ow pass 3dB corner attenuating the out-of-band noise of the bandgap. An interna 4Ω ±% resistor combines with the externa capacitor to create a singe-poe ow pass fiter. Tabe 2 ists capacitor vaues and the corresponding 3dB cutoff frequency. NOISE (n/ Hz) 2 2 C NR = µf C NR = C NR =.. 66 F3 Figure 3. LT66 Bandgap Output otage Noise Tabe 2. NR Capacitor aues and the Corresponding 3dB Frequency NR Capacitor (µf).2 NR 3dB Frequency (Hz). NR 3dB Frequency (Hz) 2., 3, 3.3, NR 3dB Frequency (Hz) The primary trade-off for incuding an RC fiter on the NR pin is a sower turn-on time. The effective resistance seen by the NR capacitor is 4Ω. The RC time constant (τ) for charging the NR capacitor is τ = R C. To reach the initia accuracy specification for the LT66,.%, it wi take 7.6τ of setting time. Exampe setting time 2

26 LT66 Appications Information constants are shown in Tabe 3. An exampe of the NR pin charging and the reationship to the output votage is shown in Figure 4. The appropriate trade-off between setting time and noise imiting is specific to the demands of each unique appication. Tabe 3. Setting Times for Different NR Capacitor aues Output otage () NR Pin Resistance (Ω) , 3, 3.3, /DI /DI NR 4 C (μf) 7.6τ (ms) INTEGRATED NOISE (µ RMS ) C OUT = C OUT = µf 4 C OUT = C NR = 22µF F Figure. LT66-2. Tota Integrated Output otage Noise with C NR = 22µF and C OUT =, µf and Output Capacitors INTEGRATED NOISE (µ RMS ) C OUT2 = C OUT2 = µf C OUT2 = C NR = 22µF /DI OUT µs/di C NR = C OUT = 66 F F6 Figure 4. Start-up Response on the NR Pin and OUT_F The LT66 s two ow noise buffer ampifiers measure n/ Hz. The combined bandgap and buffer noise resuts for Buffer and Buffer 2 are shown in the Typica Performance Characteristics section. Note that beyond the NR pin cutoff frequency, the noise is primariy due to the buffer ampifiers. As shown, the buffer can be bandimited by increasing the size of the output capacitors. Figure and Figure 6 show the tota integrated noise of Buffer and Buffer 2, respectivey. Figure 6. LT66-2. OUT2 Integrated Noise with C NR = 22µF and C OUT2 =, µf and The output votage noise does not change appreciaby as oad current increases. The wide range of output capacitance capabiity and the NR pin capacitance aows the LT66 noise density spectrum to be customized for specific appications. Tabe 4 ists the output noise for different conditions. The output and NR capacitances aso affect the AC PSRR response as shown in Tabe 4. See the Typica Performance Characteristics section for more information. 26

27 Appications Information LT66 Tabe 4. Output Noise and Rippe Rejection Typica aues PARAMETER CONDITIONS TYP UNITS Output Noise otage ( OUT and OUT2 ) Output RMS Noise Power Suppy Rejection ( = OUT + 3, 2 = OUT2 + 3) Frequency = Hz, C OUT =, C NR = F, I LOAD = Fu Current* Frequency = Hz, C OUT =, C NR =, I LOAD = Fu Current* Frequency = khz, C OUT =, C NR = F, I LOAD = Fu Current* Frequency = khz, C OUT =, C NR = F, I LOAD = Fu Current* Hz to khz, C OUT =, C NR = F Hz to khz, C OUT =, C NR = Hz to khz, C OUT = µf, C NR = 22µF Hz to khz, C OUT2 =, C NR = F Hz to khz, C OUT2 =, C NR = Hz to khz, C OUT2 = µf, C NR = 22µF RIPPLE = m P-P, f RIPPLE = 2Hz, I LOAD = ma, C OUT =, C NR = RIPPLE = m P-P, f RIPPLE = khz, I LOAD = ma, C OUT =, C NR = RIPPLE = m P-P, f RIPPLE = khz, I LOAD = ma, C OUT =, C NR = RIPPLE = m P-P, f RIPPLE = MHz, I LOAD = ma, C OUT =, C NR = RIPPLE = m P-P, f RIPPLE = 2Hz, I LOAD2 = ma, C OUT2 =, C NR = RIPPLE = m P-P, f RIPPLE = khz, I LOAD2 = ma, C OUT2 =, C NR = RIPPLE = m P-P, f RIPPLE = khz, I LOAD2 = ma, C OUT2 =, C NR = RIPPLE = m P-P, f RIPPLE = MHz, I LOAD2 = ma, C OUT2 =, C NR = * The fu current for I LOAD is ma and ma for output and output 2, respectivey n/ Hz n/ Hz n/ Hz n/ Hz ppm RMS ppm RMS ppm RMS ppm RMS ppm RMS ppm RMS db db db db db db db db Power Suppy Rejection The three suppy pins provide fexibiity to address the unique demands of each appication. When coected together, the LT66 provides exceent AC power suppy rejection. Superior performance can be achieved when the suppy pins are independenty powered. For exampe, use a separate suppy for the pin to isoate the bandgap circuit from the outputs. Further, each buffer can be suppied independenty to provide a high degree of isoation as summarized in Tabe 3. Output Disabe The OD pin disabes the output stage of both output buffers. This pin is usefu for disabing the buffers when faut conditions exist. For exampe, if externa circuitry senses that the oad is too hot or there is a short circuit condition, this pin can be asserted to remove the output current. This active ow pin wi disabe the output buffers when the votage on the pin is ess than.. When the input votage is greater than 2 the LT66 is enabed. The start-up after enabing the LT66 enabes is determined by the size of the output and NR capacitors. Figure 7 is an exampe of the LT66-2. being enabed and disabed. The OD pin has an interna pu-up current that wi keep the output buffers enabed when the OD pin foats. In noisy environments, it is recommended that OD be tied high expicity. /DI /DI /DI OD OUT OUT2 µs/di C OUT = C OUT2 = 66 F7 Figure 7. The Output Disabe Function 27

28 LT66 Appications Information Interna Protection There are two interna protection circuits for monitoring output current and die temperature. The output stage of each output buffer is disabed when the interna die temperature is greater than 6 C. There is C of hysteresis aowing the part to return to norma operation once the die temperature drops beow 4 C. In addition, a short circuit protection feature prevents the output from suppying an unimited oad current. A faut or short on either output force pin wi cause the output stage to imit the current and the output votage wi drop accordingy to the output faut condition. For exampe, if a Ω faut to ground occurs on Buffer, the circuit protection wi imit both outputs. A oad faut on either buffer wi affect the output of both buffers. The OD pin may aso be used with externa circuitry to set a atched current imit as shown in Figure. The LT6- provides a high-side current sense, atched comparator and a reference votage enabing a simpe atched overcurrent protection circuit. The high side sensing shown in Figure adds ony 7.m overhead to the suppy and is set to trip at ma. Separate suppy pins on the LT66 permit each output buffer to have a dedicated overcurrent sense circuit. The RST signa resets the atched comparator. Power Dissipation To maintain reiabe precise and accurate performance the LT66 junction temperature shoud never exceed T JMAX = C. If the part is operated at the absoute maximum input votage and maximum output currents, the MSE package wi need to dissipate over 7 watts of power. The LT66 comes in an MSE package with an exposed pad. The therma resistance junction to case, θ JC, of the MSE package is C/W. The therma resistance junction to ambient, θ JA, is determined by the amount of copper on the PCB that is sodered to the exposed pad. When foowing estabished ayout guideines the θ JA can be as ow as 3 C/W for the MSE package.. TO 36 7Ω..Ω 9 OD 4 BANDGAP LT Ω OUT_F 2 OUT_S 3 OUT2_F OUT2_S 7 OUT OUT2. 4k SENSEHI SENSELO OUTA LT6- INC + EN/RST OUTC k RST OC. BYPASS NR 3, 2, 6, 7 66 F27 Figure. LT66-2. with an Overcurrent Protection Circuit 2