LT /LT / LT High Voltage, Bidirectional Current Sense Amplifier. Applications. Typical Application

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1 + LT999-/LT999-/ High otage, Bidirectiona Current Sense Ampifier Features n Buffered Output with Gain Options: /, /, / n Gain Accuracy:.% Max n Input Common Mode otage Range: to n AC CMRR > at khz n Input Offset otage:.m Max n Bandwidth: MHz n Smooth, Continuous Operation Over Entire Common Mode Range n k HBM Toerant and k CDM Toerant n Low Power Shutdown <µa n C to C Operating Temperature Range n -Lead MSOP and -Lead SO (Narrow) Packages Appications n High Side or Low Side Current Sensing n H-Bridge Motor Contro n Soenoid Current Sense n High otage Data Acquisition n PWM Contro Loops n Fuse/MOSFET Monitoring Description The LT 999 is a high speed precision current sense ampifier, designed to monitor bidirectiona currents over a wide common mode range. The LT999 is offered in three gain options: /, /, and /. The LT999 senses current via an externa resistive shunt and generates an output votage, indicating both magnitude and direction of the sensed current. The output votage is referenced hafway between the suppy votage and ground, or an externa votage can be used to set the reference eve. With a MHz bandwidth and a common mode input range of to, the LT999 is suitabe for monitoring currents in H-Bridge motor contros, switching power suppies, soenoid currents, and battery charge currents from fu charge to depetion. The LT999 operates from an independent suppy and draws.ma. A shutdown mode is provided for minimizing power consumption. The LT999 is avaiabe in an -ead MSOP or SOP package. L, LT, LTC, LTM, Linear Technoogy and the Linear ogo are registered trademarks of Linear Technoogy Corporation. A other trademarks are the property of their respective owners. Typica Appication S LT999 Fu Bridge Armature Current Monitor R S IN IN k.k + SHDN µa R G 7 SHDN (/DI). IN +IN (/DI) k.k k REF.µF k.µf TIME (µs/di) 999 TAb 999 TAa

2 LT999-/LT999-/ Absoute Maximum Ratings Differentia Input otage +IN to IN (Notes, )... ±, ms +IN to GND, IN to GND (Note ).... to Tota Suppy otage ( to GND)... Input otage Pins and... +.,. Output Short-Circuit Duration (Note )... Indefinite Operating Ambient Temperature (Note ) LT999C... C to C LT999I... C to C LT999H... C to C LT999MP... C to C (Note ) Specified Temperature Range (Note ) LT999C... C to 7 C LT999I... C to C LT999H... C to C LT999MP... C to C Junction Temperature... C Storage Temperature Range... C to C Pin Configuration +IN IN TOP IEW SHDN 7 OUT REF GND MS PACKAGE -LEAD PLASTIC MSOP T JMAX = C, Θ JA = C/W +IN IN TOP IEW 7 S PACKAGE -LEAD PLASTIC SO T JMAX = C, Θ JA = 9 C/W SHDN OUT REF GND Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT999CMS-#PBF LT999CMS-#TRPBF LTFPB -Lead Pastic MSOP C to 7 C LT999IMS-#PBF LT999IMS-#TRPBF LTFPB -Lead Pastic MSOP C to C LT999HMS-#PBF LT999HMS-#TRPBF LTFPB -Lead Pastic MSOP C to C LT999MPMS-#PBF LT999MPMS-#TRPBF LTFQP -Lead Pastic MSOP C to C LT999CS-#PBF LT999CS-#TRPBF 999 -Lead Pastic SO C to 7 C LT999IS-#PBF LT999IS-#TRPBF 999 -Lead Pastic SO C to C LT999HS-#PBF LT999HS-#TRPBF 999 -Lead Pastic SO C to C LT999MPS-#PBF LT999MPS-#TRPBF 99MP -Lead Pastic SO C to C LT999CMS-#PBF LT999CMS-#TRPBF LTFNZ -Lead Pastic MSOP C to 7 C LT999IMS-#PBF LT999IMS-#TRPBF LTFNZ -Lead Pastic MSOP C to C LT999HMS-#PBF LT999HMS-#TRPBF LTFNZ -Lead Pastic MSOP C to C LT999MPMS-#PBF LT999MPMS-#TRPBF LTFQQ -Lead Pastic MSOP C to C

3 LT999-/LT999-/ Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT999CS-#PBF LT999CS-#TRPBF 999 -Lead Pastic SO C to 7 C LT999IS-#PBF LT999IS-#TRPBF 999 -Lead Pastic SO C to C LT999HS-#PBF LT999HS-#TRPBF 999 -Lead Pastic SO C to C LT999MPS-#PBF LT999MPS-#TRPBF 99MP -Lead Pastic SO C to C LT999CMS-#PBF LT999CMS-#TRPBF LTFPC -Lead Pastic MSOP C to 7 C LT999IMS-#PBF LT999IMS-#TRPBF LTFPC -Lead Pastic MSOP C to C LT999HMS-#PBF LT999HMS-#TRPBF LTFPC -Lead Pastic MSOP C to C LT999MPMS-#PBF LT999MPMS-#TRPBF LTFQR -Lead Pastic MSOP C to C LT999CS-#PBF LT999CS-#TRPBF 999 -Lead Pastic SO C to 7 C LT999IS-#PBF LT999IS-#TRPBF 999 -Lead Pastic SO C to C LT999HS-#PBF LT999HS-#TRPBF 999 -Lead Pastic SO C to C LT999MPS-#PBF LT999MPS-#TRPBF 99MP -Lead Pastic SO C to C Consut LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a abe on the shipping container. Consut LTC Marketing for information on non-standard ead based finish parts. For more information on ead free part marking, go to: For more information on tape and ree specifications, go to: Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, C < T A < 7 C for C-grade parts, C < T A < C for I-grade parts, and C < T A < C for H-grade parts, otherwise specifications are at T A = C. =, GND =, CM =, REF = foating, SHDN = foating, uness otherwise specified. See Figure. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS SENSE Fu-Scae Input Sense otage (Note 7) SENSE = IN IN LT999- LT999- CM CM Input otage Range R IN(DIFF) Differentia Input Impedance Δ INDIFF = ±/Gain. 9. kω R INCM CM Input Impedance Δ CM =. to Δ CM = to. OSI Input Referred otage Offset ± 7 Δ OSI /ΔT Input Referred otage Offset Drift μ/ C A Gain LT999- LT999- A Error Gain Error Δ = ±. ±.. % I B Input Bias Current I(+IN) = I(IN) (Note ) CM >. CM = SHDN =., < CM < μa ma μa I OS Input Offset Current I OS = I(+IN) I(IN) (Note ) CM >. CM = SHDN =., < CM < PSRR Suppy Rejection Ratio =. to MΩ kω μ μ / / / μa μa μa

4 LT999-/LT999-/ Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, C < T A < 7 C for C-grade parts, C < T A < C for I-grade parts, and C < T A < C for H-grade parts, otherwise specifications are at T A = C. =, GND =, CM =, REF = foating, SHDN = foating, uness otherwise specified. See Figure. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS CMRR Sense Input Common Mode Rejection CM = to CM = to. CM =, 7 P-P, f = khz, CM =, 7 P-P, f = khz e n Differentia Input Referred Noise otage Density f = khz f =.Hz to Hz REF RR REF Pin Rejection, =. Δ REF =. Δ REF =. Δ REF =. R REF REF Pin Input Impedance LT999- LT n/ Hz μ P-P SHDN =.. REF Open Circuit otage. SHDN =..7 REFR REF Pin Input Range (Note 9) LT999-. LT I SHDN Pin Pu-Up Current =., SHDN = μa IH SHDN Pin Input High. IL SHDN Pin Input Low. f Sma Signa Bandwidth LT999- LT999- SR Sew Rate /μs t s Setting Time due to Input Step, Δ = ±.% Setting. μs t r Common Mode Step Recovery Time Δ CM = ±, ns (Note ) LT999- LT μs μs μs S Suppy otage (Note ).. I S Suppy Current CM >. CM = =., SHDN =., CM > R O Output Impedance ΔI O = ±ma. Ω I SRC Sourcing Output Current R LOAD = Ω to GND ma I SNK Sinking Output Current R LOAD = Ω to ma Swing Output High (with Respect to ) R LOAD = kω to Mid-Suppy R LOAD = Open Swing Output Low (with Respect to ) R LOAD = kω to Mid-Suppy R LOAD = Open t ON Turn-On Time SHDN = to μs t OFF Turn-Off Time SHDN = to μs kω MΩ MHz MHz MHz ma ma μa m m m m

5 LT999-/LT999-/ Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, C < T A < C for MP-grade parts, otherwise specifications are at T A = C. =, GND =, CM =, REF = foating, SHDN = foating, uness otherwise specified. See Figure. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS SENSE Fu-Scae Input Sense otage (Note 7) SENSE = IN IN LT999- LT999- CM CM Input otage Range R IN(DIFF) Differentia Input Impedance Δ INDIFF = ±/GAIN. 9. kω R INCM CM Input Impedance Δ CM =. to Δ CM = to. OSI Input Referred otage Offset ± 7 Δ OSI /ΔT Input Referred otage Offset Drift μ/ C A Gain LT999- LT999- A Error Gain Error Δ = ±. ±.. % I B Input Bias Current I(+IN) = I(IN) (Note ) CM >. CM = SHDN =., < CM < μa ma μa I OS Input Offset Current I OS = I(+IN) I(IN) (Note ) CM >. CM = SHDN =., < CM < PSRR Suppy Rejection Ratio =. to. 77 CMRR Sense Input Common Mode Rejection CM = to CM = to. CM =, 7 P-P, f = khz, CM =, 7 P-P, f = khz e n Differentia Input Referred Noise otage Density f= khz f =.Hz to Hz REF RR REF Pin Rejection, =. Δ REF =.7 Δ REF =. Δ REF =. R REF REF Pin Input Impedance LT999- LT MΩ kω μ μ / / / μa μa μa n/ Hz μ P-P SHDN =.. REF Open Circuit otage. SHDN =..7 REFR REF Pin Input Range (Note 9) LT999-. LT I SHDN Pin Pu-Up Current =., SHDN = μa IH SHDN Pin Input High. IL SHDN Pin Input Low. f Sma Signa Bandwidth LT999- LT999- SR Sew Rate /μs t S Setting Time Due to Input Step, Δ = ±.% Setting. μs. kω MΩ MHz MHz MHz

6 LT999-/LT999-/ Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, C < T A < C for MP-grade parts, otherwise specifications are at T A = C. =, GND =, CM =, REF = foating, SHDN = foating, uness otherwise specified. See Figure. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS t r Common Mode Step Recovery Time Δ CM = ±, ns (Note ) LT999- LT μs μs μs S Suppy otage (Note ).. I S Suppy Current CM >. CM = =., SHDN =., CM > R O Output Impedance ΔI O = ±ma. Ω I SRC Sourcing Output Current R LOAD = Ω to GND ma I SNK Sinking Output Current R LOAD = Ω to ma Swing Output High (with Respect to ) R LOAD = kω to Mid-Suppy R LOAD = Open Swing Output Low (with Respect to ) R LOAD = kω to Mid-Suppy R LOAD = Open t ON Turn-On Time SHDN = to μs t OFF Turn-Off Time SHDN = to μs ma ma μa m m m m 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 : Pin (+IN) and Pin (IN) are protected by ESD votage camps which have asymmetric bidirectiona breakdown characteristics with respect to the GND pin (Pin ). These pins can safey support common mode votages which vary from. to without triggering an ESD camp. Note : Exposure to differentia sense votages exceeding the norma operating range for extended periods of time may degrade part performance. A heat sink may be required to keep the junction temperature beow the Absoute Maximum Rating when the inputs are stressed differentiay. The amount of power dissipated in the LT999 due to input overdrive can be approximated by: ( P DISS = IN IN ) kω Note : A heat sink may be required to keep the junction temperature beow the absoute maximum rating. Note : The LT999C/LT999I are guaranteed functiona over the operating temperature range C to C. The LT999H is guaranteed functiona over the operating temperature range C to C. The LT999MP is guaranteed functiona over the operating temperature range C to C. Junction temperatures greater than C wi promote acceerated aging. The LT999 has a demonstrated typica ife beyond hours at C. Note : The LT999C is guaranteed to meet specified performance from C to 7 C. The LT999C is designed, characterized, and expected to meet specified performance from C to C but is not tested or QA samped at these temperatures. The LT999I is guaranteed to meet specified performance from C to C. The LT999H is guaranteed to meet specified performance from C to C. The LT999MP is guaranteed to meet specified performance from C to C. Note 7: Fu-scae sense ( SENSE ) gives indication of the maximum differentia input that can be appied with better than.% gain accuracy. Gain accuracy is degraded when the output saturates against either power suppy rai. SENSE is verified with =., CM =, with the REF pin set to it s votage range imits. The maximum SENSE is verified with the REF pin set to it s minimum specified imit, verifying the gain error is ess than.% at the output. The minimum SENSE is verified with the REF pin set to its maximum specified imit, verifying the gain error at the output is ess than.%. See Note 9 for more information. Note : I B is defined as the average of the input bias currents to the +IN and IN pins (Pins and ). A positive current indicates current fowing into the pin. I OS is defined as the difference of the input bias currents. I OS = I(+IN) I(IN) Note 9: The REF pin votage range is the minimum and maximum imits that ensures the input referred votage offset does not exceed ±m over the I, C, and H temperature ranges, and ±.m over the MP temperature range. Note : Common mode recovery time is defined as the time it takes the output of the LT999 to recover from a, ns input common mode votage transition, and sette to within the DC ampifier specifications. Note : Operating the LT999 with <. is possibe, athough the LT999 is not tested or specified in this condition. See the Appications Information section.

7 Typica Performance Characteristics LT999-/LT999-/ I S (ma) 7 Suppy Current vs Input Common Mode Suppy Current vs Temperature Suppy Current vs Suppy otage = I S (ma)..7.. SHDN = OPEN INDIFF = CM = =. =. I S (ma) C C 9 C C C C CM = CM () G. 7 9 TEMPERATURE ( C) 999 G SUPPLY OLTAGE () 999 G I S (ma)... Suppy Current vs SHDN Pin otage = CM = T A = C T A = C T A = C SHDN () 999 G I S (µa) Shutdown Suppy Current vs Temperature SHDN = INDIFF = CM = =. =. 7 9 TEMPERATURE ( C) 999 G I B (na) Shutdown Input Bias Current vs Input Common Mode = SHDN = SENSE = T A = C T A = C T A = C T A = 9 C T A = 7 C CM () 999 G I B (ma).... Input Bias Current vs Input Common Mode = I B (µa) Input Bias Current vs Temperature SHDN = OPEN INDIFF = = CM = CM =. IMPEDANCE (kω) Input Impedance vs Input Common Mode otage COMMON MODE INPUT IMPEDANCE DIFFERENTIAL INPUT IMPEDANCE. CM () G7 7 9 TEMPERATURE ( C) 999 G CM () G9 7

8 LT999-/LT999-/ Typica Performance Characteristics Input Referred otage Offset vs Temperature and Gain Option CM = UNITS PLOTTED Input Referred otage Offset vs Input Common Mode otage = T A = C UNITS PLOTTED OSI (µ) OSI (µ) LT999- LT TEMPERATURE ( C) 999 G LT999- LT999- CM () G LT999- Sma Signa Frequency Response LT999- Sma Signa Frequency Response GAIN 9 GAIN 9 GAIN () PHASE PHASE (DEG) GAIN () PHASE PHASE (DEG) 9 9 =. P-P AT khz FREQUENCY (khz) 999 G =. P-P AT khz FREQUENCY (khz) 999 G Sma Signa Frequency Response GAIN 9.. Gain Error vs Temperature CM = UNITS PLOTTED.. Gain Error vs Input Common Mode otage = T A = C UNITS PLOTTED GAIN () PHASE PHASE (DEG) GAIN ERROR (%) GAIN ERROR (%) =. P-P AT khz FREQUENCY (khz) G.. LT999- LT TEMPERATURE ( C) 999 G.. LT999- LT999- CM () G

9 Typica Performance Characteristics LT999-/LT999-/ LT999- Puse Response LT999- Puse Response Puse Response SENSE SENSE SENSE SENSE (./DI) (/DI) SENSE (./DI) (/DI) SENSE (./DI) (/DI) TIME (µs/di) 999 G7 TIME (µs/di) 999 G TIME (µs/di) 999 G9. LT999- Step Response Setting Time.. LT999- Step Response Setting Time ().... OUTPUT ERROR... OUTPUT ERROR () ().... OUTPUT ERROR... OUTPUT ERROR () TIME (µs/di) 999 G TIME (µs/di) 999 G () Step Response Setting Time OUTPUT ERROR TIME (µs/di) 999 G OUTPUT ERROR () CMRR () CMRR vs Frequency CM = = T A = C UNITS PLOTTED FREQUENCY (khz) LT999- LT G CMRR () CMRR vs Frequency CM = = T A = C UNITS PLOTTED FREQUENCY (khz) LT999- LT G 9

10 LT999-/LT999-/ Typica Performance Characteristics LT999- Common Mode Rising Edge Step Response LT999- Common Mode Faing Edge Step Response CM, t RISE ns CM, t FALL ns (./DI) CM (/DI) (./DI) CM (/DI) TIME (.µs/di) 999 G TIME (.µs/di) 999 G LT999- Common Mode Rising Edge Step Response LT999- Common Mode Faing Edge Step Response CM, t RISE ns (./DI) CM (/DI) (./DI) CM, t FALL ns CM (/DI) TIME (.µs/di) 999 G7 TIME (.µs/di) 999 G Common Mode Rising Edge Step Response Common Mode Faing Edge Step Response CM, t RISE ns (./DI) CM (/DI) (./DI) CM, t FALL ns CM (/DI) TIME (.µs/di) 999 G9 TIME (.µs/di) 999 G

11 Typica Performance Characteristics LT999-/LT999-/ LT999 Input Referred Noise Density vs Frequency Short-Circuit Current vs Temperature. REF Open Circuit otage vs Temperature NOISE DENSITY (n/ Hz)... FREQUENCY (khz) 999 G I SC (ma) SINKING SOURCING 7 9 TEMPERATURE ( C) 999 G REF PIN OLTAGE () ACTIE MODE. SHDN MODE.... = 7 9 TEMPERATURE ( C) 999 G SHDN Pin Current vs SHDN Pin otage and Temperature = CM = Turn-On/Turn-Off Time vs SHDN otage CM = I SHDN (µa) T A = C T A = C T A = C I S (ma/di) SHDN I S SHUTDOWN SHDN PIN OLTAGE (/DI) SHDN () 999 G TIME (µs/di) 999 G vs SENSE REF =. vs SENSE Over the Sense ABSMAX Range PHASE REERSAL FOR SENSE < () ()..... SENSE () LT999- LT G LT999- LT999- REF =. SENSE () 999 G7

12 LT999-/LT999-/ Pin Functions (Pins, ): Power Suppy otage. Pins and are tied internay together. The specified range of operation is. to., but ower suppy votages (down to approximatey ) is possibe athough the LT999 is not tested or characterized beow.. See the Appications Information section. +IN (Pin ): Positive Sense Input Pin. IN (Pin ): Negative Sense Input Pin. GND (Pin ): Ground Pin. REF (Pin ): Reference Pin Input. The REF pin sets the output common mode eve and is set hafway between and GND using a divider made of two k resistors. The defaut open circuit potentia of the REF pin is mid-suppy. It can be overdriven by an externa votage source cabe of driving k to a mid-suppy potentia (see the Eectrica Characteristics tabe for its specified input votage range). OUT (Pin 7): otage Output. = A ( SENSE ± OSI ), where A is the gain, and OSI is the input referred offset votage. The output ampifier has a ow impedance output and is designed to drive up to pf capacitive oads directy. Capacitive oads exceeding pf shoud be decouped with an externa resistor of at east Ω. SHDN (Pin ): Shutdown Pin. When pued to within. of GND (Pin ), wi pace the LT999 into ow power shutdown. If the pin is eft foating, an interna µa puup current source wi pace the LT999 into the active (ampifying) state.

13 + + Bock Diagram LT999-/LT999-/ SHDN µa.k +IN IN k k R +IN k C F pf k.k R +S.k R S (G +IN ) (G IN ) + D G IN + R G A O OUT + Ω k REF 7 R IN k GND 999 BD Figure. Simpified Bock Diagram Test Circuit CM IN(DIFF) k k.k.k + LT999 SHDN µa R G k 7 SHDN REF k.µf.µf 999 F Figure. Test Circuit

14 LT999-/LT999-/ Appications Information The LT999 current sense ampifier provides accurate bidirectiona monitoring of current through a user-seected sense resistor. The votage generated by the current fowing in the sense resistor is ampified by a fixed gain of /, / or / (LT999-, LT999-, or respectivey) and is eve shifted to the OUT pin. The votage difference and poarity of the OUT pin with respect to REF (Pin ) indicates magnitude and direction of the current in the sense resistor. THEORY of OPERATION Refer to the Bock Diagram (Figure ). Case : < CM < For input common mode votages exceeding the power suppy, one can assume D of Figure is competey off. The sensed votage ( SENSE ) is appied across Pin (+IN) and Pin (IN) to matched resistors R +IN and R IN (nominay k each). The opposite ends of R +IN and R IN are forced to equa potentias by transconductor G IN, which convert the differentiay sensed votage into a sensed current. The sensed current in R +IN and R IN is combined, eve-shifted, and converted back into a votage by transresistance ampifier A O and resistor R G. Ampifier A O provides high open oop gain to accuratey convert the sensed current back into a votage and to drive externa oads. The theoretica output votage is determined by the sensed votage ( SENSE ), and the ratio of two on-chip resistors: where REF = SENSE R G R IN The votage difference between the OUT pin and the REF pin represent both poarity and magnitude of the sensed votage. The noninverting input of ampifier A O is biased by a resistive k to k divider tied between and GND to set the defaut REF pin bias to mid-suppy. Case : < CM < For common mode inputs which transition or are set beow the suppy votage, diode D wi turn on and wi provide a source of current through R +S and R S to bias the inputs of transconductance ampifier G IN at east. above GND. The transition is smooth and continuous; there are negigibe changes to either gain or ampifier votage offset. The ony difference in ampifier operation is the bias currents provided by D through R +S and R S are steered through the input pins, otherwise ampifier operation is identica. The inputs to transconductance ampifier G IN are sti forced to equa potentias forcing any differentia votages appearing at the +IN and IN pins into a differentia current. This differentia current is combined, eve-shifted, and converted back into a votage by trans-resistance ampifier A O and Resistor R G. Resistors R +S and R S are trimmed to match R +IN and R IN respectivey, to prevent common mode to differentia conversion from occurring (to the extent of the matched trim) when the input common mode transitions beow. As described in case, the output is determined by the sense votage and the ratio of two on-chip resistors: where REF = SENSE R G R IN R IN = R +IN + R IN nominay k R IN = R +IN + R IN For the LT999-, R G is nominay k. For the LT999-, R G is nominay k, and for the, R G is nominay k.

15 Appications Information Input Common Mode Range The LT999 was optimized for high common mode rejection. Its input stage is baanced and fuy differentia, designed to ampify differentia signas and reject common mode signas. There is negigibe crossover distortion due to sense votage reversas. The ampifier is most inear in the zero-sense region. With the suppy configured within the specified and tested range (. < <.), the LT999 s common mode range extends from to. Pushing +IN and IN beyond the imits specified in the Absoute Maximum tabe can turn on the votage camps designed to protect the +IN and IN pins during ESD events. It is possibe to operate the LT999 on power suppies as ow as (athough it is not tested or specified beow.). Operating the LT999 on suppies beow wi produce erratic behavior. When operating the LT999 with suppies as ow as, the common mode range for inputs which extend beow GND is reduced. Refer to the Bock Diagram (Figure ). For inputs driven beow, diode D conducts. For proper operation, the input to the transconductor (G +IN ) must be biased at approximatey. above the GND pin. (G +IN ) sits on the centertap of a votage divider comprised of R +S and R +IN (G IN ) ikewise sits in the midde of the votage divider comprised of R S, and R IN ). The votage on (G +IN ) input is given by the foowing equation: R +S ( ) R +IN (G +IN ) = IN + R +S + R D +IN R +S + R +IN Setting (G +IN ) =., the ratio (R +IN /R +S ) to, and D equa to. (cod temperatures), a pot of the ower input common mode range potted against suppy is shown in Figure. CM(LOWER LIMIT) () LT999-/LT999-/ BELOW GROUND INPUT COMMON MODE RANGE LIMITED BY SUPPLY OLTAGE BELOW GROUND INPUT COMMON MODE RANGE LIMITED BY ESD CLAMPS TYPICAL ESD CLAMP OLTAGE SUPPLY OLTAGE () 999 F Figure. Lower Input Common Mode vs Suppy otage Output Common Mode Range The LT999 s output common mode eve is set by the votage on the REF pin. The REF pin sits in the midde of a k to k votage divider connected between and GND which sets the defaut open circuit potentia of the REF pin to mid-suppy. It can be overdriven by an externa votage source capabe of driving k tied to a mid-suppy potentia. See the Eectrica Characteristics tabe for the REF pin s specified input votage range. Differentia samping of the OUT pin with respect the REF pin provides the best noise immunity. Measurements of the output votage made differentiay with respect to the REF pin wi provide the highest power suppy and common mode rejection. Otherwise, power suppy or GND pin disturbances are divided by the REF pin s votage divider and appear directy at the noninverting input of the transresistance ampifier A O and are not rejected. If not driven by a ow impedance (<Ω), the REF pin shoud be fitered with at east nf of capacitance to a ow impedance, ow noise ground pane. This externa capacitance wi aso provide a charge reservoir during high frequency samping of the REF pin by ADC inputs attached to this pin.

16 LT999-/LT999-/ Appications Information Shutdown Capabiity If SHDN (Pin ) is driven to within. of GND, the LT999 is paced into a ow power shutdown state in which the part wi draw about μa from the suppy. The input pins (+IN and IN) wi draw approximatey na if biased within the range of to (with no differentia votage appied). If the input pins are pued beow the GND pin, each input appears as a diode tied to GND in series with approximatey k of resistance. The REF pin appears as approximatey.mω tied to a mid-suppy potentia. The output appears as reverse biased diodes tied between the output to either or GND pins. EMI Fitering and Layout Practices An interna st order differentia owpass noise/emi suppression fiter with a bandwidth of MHz (approximatey the LT999 s bandwidth) is incuded to hep improve the LT999 s EMI susceptibiity and to assist with the rejection of high frequency signas beyond the bandwidth of the LT999 that may introduce errors. The poe is set by the foowing equation: f fit = /(π (R +IN + R IN ) C F ) MHz Both the resistors and capacitors have a ±% variation so the poe can vary by approximatey ±% over manufacturing process and temperature variations. The ayout for owest EMI/noise susceptibiity is achieved by keeping short direct connections and minimizing oop areas (see Figure ). If the user-suppied sense resistor cannot be paced in cose proximity to the LT999, the surface area of the oop comprising connections of +IN to R SENSE and back to IN shoud be minimized. This requires routing PCB traces connecting +IN to R SENSE and IN to R SENSE adjacent with one another with minima separation. The meta traces connecting +IN to the sense resistor and IN to the sense resistor shoud match and use the same trace width. Bypassing the pin to the GND pin with a.µf capacitor with short wiring connection is recommended. FROM DC SOURCE R SENSE * +IN IN SHDN OUT REF GND 7 DIFFERENTIAL ANALOG OUT TO LOAD ** SUPPLY BYPASS CAPACITOR 999 F * KEEP LOOP AREA COMPRISING R SENSE, +IN AND IN PINS AS SMALL AS POSSIBLE. ** REF BYPASS TIED TO A LOW NOISE, LOW IMPEDANCE SIGNAL GROUND PLANE. OPTIONAL pf CAPACITOR TO PREENT d/dt EDGES ON INPUT COUPLING TO FLOATING SHDN PIN. Figure. Recommended Layout

17 Appications Information The REF pin shoud be either driven by a ow source impedance (<Ω) or shoud be bypassed with at east nf to a ow impedance, ow noise, signa ground pane (see Figure ). Larger bypass capacitors on both pins, and the REF pin, wi extend enhanced AC CMRR, and PSRR performance to ower frequencies. Bypassing the REF pin to a quiet ground pane fiters the pin or GND pin noise that is sensed by the REF pin votage divider and appied to the noninverting input of output ampifier A O. Any common I R drops generated by pusating ground currents in common with the REF pin fiter capacitor can compromise the fitering performance and shoud be avoided. If the SHDN pin is not driven and is eft foating, routing a PCB trace connecting Pins and under the part wi act as a shied, and wi hep imit edge couping from the inputs (Pins and ) to the SHDN pin. Periodic puses on the inputs with fast edges may gitch the high impedance SHDN pin, periodicay putting the part into ow power shutdown. Additiona precaution against this may be taken by adding an optiona sma (~pf) capacitor may be tied between (Pin ) and Pin. Finay, when connecting the LT999 inputs to the sense resistor, it is important to use good Kevin sensing practices (sensing the resistor in a way that excudes PCB trace I R votage drops). For sense resistors ess than Ω, one might consider using a -wire sense resistor to sense the resistive eement accuratey. LT999-/LT999-/ Seection of the Current Sense Resistor The externa sense resistor seection presents a deicate trade-off between power dissipation in the resistor and current measurement accuracy. In high current appications, the user may want to minimize the power dissipated in the sense resistor. The sense resistor current wi create heat and votage oss, degrading efficiency. As a resut, the sense resistor shoud be as sma as possibe whie sti providing adequate dynamic range required by the measurement. The dynamic range is the ratio between the maximum accuratey produced signa generated by the votage across the sense resistor, and the minimum accuratey reproduced signa. The minimum accuratey reproduced signa is primariy dictated by the votage offset of the LT999. The maximum accuratey reproduced signa is dictated by the output swing of the LT999. Thus the dynamic range for the LT999 can be thought of the maximum sense votage divided by the input referred votage offset or: Dynamic Range = (MAX) GAIN OSI The above equation tes us that the dynamic range is inversey proportiona to the gain of the LT999. Thus, if accuracy is of greater importance than efficiency or power oss, the LT999- used with the highest vaued sense resistor possibe is recommended. If efficiency, heat generated, and power oss in the resistive shunt is the primary concern, the and the owest vaue sense resistor possibe is recommended. The LT999- is avaiabe for appications somewhere in between these two extremes. 7

18 + LT999-/LT999-/ Appications Information Fuse Monitor The inputs can be overdriven without fear of damaging the LT999. This makes the LT999 idea for monitoring fuses if either +IN or IN are shorted to ground whie the other is at the fu common mode suppy votage (see Figure ). If the fuse in Figure opens with the +IN tied to the positive suppy, the oad wi pu IN to GND. The output wi be forced to the positive suppy rai. If it is desired that the output be near ground if the fuse opens, it is a simpe matter of swapping the inputs. Precautions shoud be foowed: First, when the inputs are stressed differentiay due to the fuse bowing open, a arge votage drop wi be paced across the +IN to IN pins, dissipating power in the precision on-chip input resistors. Precaution shoud be taken to prevent junction temperatures from exceeding the Absoute Maximum ratings (see Note in the Eectrica Characteristics section). Secondy, if the oad is inductive, and the fuse bows open without a camp diode, energy stored in the inductive oad wi be dissipated in the LT999, which coud cause damage. A simpe steering diode as shown in Figure wi prevent this from happening, and wi protect the LT999 from damage. Finay, the user shoud be aware that in fuse monitoring appications with the sense votage ( SENSE = IN IN ) being driven in excess of, the output of the LT999 wi undergo phase reversa (see Figure ). ON OFF S SHDN I LOAD IN FUSE k.k + LT999 SHDN µa R G 7 SHDN REF R SENSE IN k.k k REF LOAD STEERING DIODE k.µf.µf 999 F Figure. Using the LT999 to Monitor a Fuse PHASE REERSAL FOR SENSE < (/DI) REF =. SENSE () 999 F Figure. A Pot of the LT999 s Output otage vs SENSE ( SENSE = IN IN). In Appications Where the Sense otage Is Driven in Excess of, the Output of the LT999 Wi Undergo Phase Reversa

19 + LT999-/LT999-/ Typica Appications Soenoid Current Monitor The soenoid of Figure 7 consists of a coi of wire in an iron case with permeabe punger that acts as a movabe eement. When the MOSFET turns on, the diode is reversed biased off, and current fows through R SENSE to actuate the soenoid. If the MOSFET is turned off, the current in the MOSFET is interrupted, but the energy stored in the soenoid causes the diode to turn on and current to freewhee in the oop consisting of the diode, R SENSE and the soenoid. Figure 7 shows the LT999 monitoring currents in a ground referenced soenoid used when the coi is hard tied to the case, and is tied to ground. Figure shows a suppy referenced soenoid whose coi is insuated from the case. The LT999 wi interface equay we to either of these two configurations. Bidirectiona PWM Motor Monitor Puse width moduation is commony used to efficienty vary the average votage appied across a DC motor. The H-bridge topoogy of Figure 9 aows fu -quadrant contro: cockwise contro, counter-cockwise contro, cockwise regeneration, and counter-cockwise regeneration. The LT999 in conjunction with a non-inductive current shunt is used to monitor currents in the rotor. The LT999 can be used to detect stuck rotors, provide detection of overcurrent conditions in genera, or provide current mode feedback contro. Figure shows a pot of the output votage of the LT999. S LT999 OFF ON SHDN µa SHDN IN R SENSE IN SOLENOID k k.k.k + R G k k 7 REF.µF (./DI) SOLENOID RELEASES SOLENOID PLUNGER PULLS IN IN. IN (/DI).µF 999 F7a TIME (ms/di) 999 F7b Figure 7. Soenoid Current Monitor for Ground Tied Soenoid. The Common Mode Inputs to the LT999 Switch Between S and One Diode Drop Beow Ground 9

20 + LT999-/LT999-/ Typica Appications S LT999 OFF ON SOLENOID IN R SENSE IN.µF k k.k.k + SHDN µa R G k k 7 SHDN REF.µF (./DI) SOLENOID RELEASES SOLENOID PLUNGER PULLS IN IN. IN (/DI) 999 Fa TIME (ms/di) 999 Fb Figure. Soenoid Current Monitor for Non-Grounded Soenoids. This Circuit Performs the Same Function as Figure 7 Except One End of the Soenoid Is Tied to S. The Common Mode otage of Inputs of the LT999 Switch Between Ground and One Diode Drop Above S

21 + LT999-/LT999-/ Typica Appications C µf µf IN IN k.k LT SHDN µa k 7 SHDN.µF H-BRIDGE BRIDGE k.k k REF PWM INPUT k.µf PWM IN DIRECTION OUTA R SENSE.Ω 999 F9 BRAKE INPUT OUTB MOTOR GND Figure 9. Armature Current Monitor for DC Motor Appications. (/DI) IN IN (/DI) TIME (µs/di) 999 F Figure. LT999 Output Waveforms for the Circuit of Figure 9

22 LT999-/LT999-/ Package Description Pease refer to for the most recent package drawings. MS Package -Lead Pastic MSOP (Reference LTC DWG # -- Rev F). ±. (. ±.) (NOTE ) 7. (.) REF. (.) MIN. ±. (. ±.) TYP.9 ±.7 (. ±.).. (..). (.) BSC GAUGE PLANE. (.7). (.) DETAIL A TYP. ±. (. ±.) DETAIL A RECOMMENDED SOLDER PAD LAYOUT NOTE:. DIMENSIONS IN MILLIMETER/(INCH). DRAWING NOT TO SCALE. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED.mm (.") PER SIDE. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED.mm (.") PER SIDE. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE.mm (.") MAX SEATING PLANE.9 ±. (.9 ±.). (.) MAX.. (.9.) TYP. (.) BSC. ±. (. ±.) (NOTE ). (.) REF. ±. (. ±.) MSOP (MS) 7 RE F S Package -Lead Pastic Sma Outine (Narrow. Inch) (Reference LTC DWG # --). BSC. ± (..) NOTE 7. MIN. ±... (.79.97)..7 (..9) NOTE. ±. TYP RECOMMENDED SOLDER PAD LAYOUT.. (..).. (..) TYP..9 (..7).. (..)....9 (..7) (..) NOTE: INCHES TYP. DIMENSIONS IN (MILLIMETERS). DRAWING NOT TO SCALE. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED." (.mm). (.7) BSC SO

23 LT999-/LT999-/ Revision History RE DATE DESCRIPTION PAGE NUMBER A / Revised +IN and IN pin descriptions in Pin Functions section B / Revised otage Output Swing Low specification ( ) under a oaded condition of kω to mid-suppy. Updated Figure to muticoor., Information furnished by Linear Technoogy Corporation is beieved to be accurate and reiabe. However, no responsibiity is assumed for its use. Linear Technoogy Corporation makes no representation that the interconnection of its circuits as described herein wi not infringe on existing patent rights.

24 + LT999-/LT999-/ Typica Appication Battery Charge Current and Load Current Monitor =./A, Maximum Measured Current ±9.A CHARGER.Ω LOAD IN IN k k.k.k LT SHDN µa k k 7.µF SHDN REF + BAT +IN IN CC REF LTC-.µF µf CS SCK SDO k.µf.µf 999 TA Reated Parts PART NUMBER DESCRIPTION COMMENTS LT77/ Precision, Bidirectiona High Side Current Sense Ampifier.7 to Operation, 7μ Offset, μa Current Draw LT77H LT Gain-Seectabe High Side Current Sense Ampifier. to Operation, Pin-Seectabe Gain: /,./, /, /, /, / LTC/ High otage High Side Current Sense Ampifier to / to Operation, Externa Resistor Set Gain, SOT LTCH LTC/ LTCH Zero Drift High Side Current Sense Ampifier to / to Operation, ±μ Offset, μs Step Response, MSOP/DFN Packages LTC Dua High Side Precision Current Sense Ampifier to, Gain Configurabe, -Pin MSOP Package LTC Bidirectiona, High Side Current Sense to, Gain Configurabe, -Pin MSOP Package LT Low Cost, High Side Precision Current Sense Ampifier.7 to, Gain Configurabe, SOT Package LT Precision, Extended Input Range Current Sense Ampifier. to, Gain Configurabe, -Pin MSOP Package LTC Couomb Counter/Battery Gas Gauge Indicates Charge Quantity and Poarity LT99 Precision, μa Gain Seectabe Ampifier.7 to Operation, CMRR > 7, Input otage = ± LT99 ± Input Range Difference Ampifier.7 to Operation, μ Offset, CMRR > 7B, Input otage = ± LT7/LT./.MHz,./μs Over-The-Top, Rai-to-Rai Input and Output Ampifier./μs Sew Rate, μa per Ampifier LT RE B PRINTED IN USA Linear Technoogy Corporation McCarthy Bvd., Mipitas, CA 9-77 () -9 FAX: () -7 LINEAR TECHNOLOGY CORPORATION