DESCRIPTIO APPLICATIO S TYPICAL APPLICATIO. LT1764 Series 3A, Fast Transient Response, Low Noise, LDO Regulators FEATURES

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1 A, Fast Transient Response, Low Noise, LDO Regulators FEATURES Optimized for Fast Transient Response Output Current: A Dropout Voltage: mv at A Low Noise: µv RMS (Hz to khz) ma Quiescent Current Wide Input Voltage Range:.7V to V No Protection Diodes Needed Controlled Quiescent Current in Dropout Fixed Output Voltages:.V,.8V,.V,.V Adjustable Output from.v to V <µa Quiescent Current in Shutdown Stable with µf Output Capacitor Reverse Battery Protection No Reverse Current Thermal Limiting Available in -Lead TO-, DD and 6-Lead TSSOP Packages APPLICATIO S U.V to.v Logic Power Supply Post Regulator for Switching Supplies DESCRIPTIO U The LT 76 is a low dropout regulator optimized for fast transient response. The device is capable of supplying A of output current with a dropout voltage of mv. Operating quiescent current is ma, dropping to <µa in shutdown. Quiescent current is well controlled; it does not rise in dropout as it does with many other regulators. In addition to fast transient response, the LT76 has very low output voltage noise which makes the device ideal for sensitive RF supply applications. Output voltage range is from.v to V. The LT76 regulators are stable with output capacitors as low as µf. Internal protection circuitry includes reverse battery protection, current limiting, thermal limiting and reverse current protection. The device is available in fixed output voltages of.v,.8v,.v,.v and as an adjustable device with a.v reference voltage. The LT76 regulators are available in -lead TO-, DD and Exposed Pad 6-lead TSSOP packages., LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6, 686. TYPICAL APPLICATIO U.V IN to.v OUT Regulator Dropout Voltage V IN > V µf IN OUT LT76-. SHDN SENSE µf.v A 76 TA DROPOUT VOLTAGE (mv) LOAD CURRENT (A) 76 TA

2 ABSOLUTE MAXIMUM RATINGS W W W PACKAGE/ORDER INFORMATION U U W U (Note ) IN Pin Voltage... ±V OUT Pin Voltage... ±V Input to Output Differential Voltage (Note )... ±V SENSE Pin Voltage... ±V ADJ Pin Voltage... ±7V SHDN Pin Voltage... ±V Output Short-Circuit Duration... Indefinite Operating Junction Temperature Range C to C Storage Temperature Range... 6 C to C Lead Temperature (Soldering, sec)... C TOP VIEW TAB IS FRONT VIEW Q PACKAGE -LEAD PLASTIC DD *PIN = SENSE FOR LT76-./LT76-.8/ LT76-./LT76-. = ADJ FOR LT76 T JMAX = C, θ JA = C/ W SENSE/ADJ* OUT IN SHDN TAB IS FRONT VIEW T PACKAGE -LEAD PLASTIC TO- *PIN = SENSE FOR LT76-./LT76-.8/ LT76-./LT76-. = ADJ FOR LT76 T JMAX = C, θ JA = C/ W SENSE/ ADJ* OUT IN SHDN NC OUT OUT OUT SENSE/ADJ* NC IN IN IN NC SHDN 9 FE PACKAGE 6-LEAD PLASTIC TSSOP EXPOSED PAD (PIN 7) IS. MUST BE SOLDERED TO THE PCB. *PIN 6 = SENSE FOR LT76-./ LT76-.8/LT76-./ LT76-. = ADJ FOR LT76 T JMAX = C, θ JA = 8 C/ W ORDER PART NUMBER ORDER PART NUMBER ORDER PART NUMBER FE PART MARKING LT76EQ LT76EQ-. LT76EQ-.8 LT76EQ-. LT76EQ-. LT76ET LT76ET-. LT76ET-.8 LT76ET-. LT76ET-. LT76EFE LT76EFE-. LT76EFE-.8 LT76EFE-. LT76EFE-. 76EFE 76EFE 76EFE8 76EFE 76EFE Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: Consult LTC Marketing for parts specified with wider operating temperature ranges.

3 ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are T A = C. (Note ) PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage I LOAD =.A.7 V (Notes, ) I LOAD =.A.9 V I LOAD =.7A, C < T J C..7 V I LOAD = A, C T J C..7 V Regulated Output Voltage LT76-. V IN =.V, I LOAD = ma.77.. V (Note ).7V < V IN < V, ma < I LOAD < A, C T J C.7.. V.7V < V IN < V, ma < I LOAD <.7A, C < T J C.7.. V LT76-.8 V IN =.V, I LOAD = ma V.8V < V IN < V, ma < I LOAD < A, C T J C V.8V < V IN < V, ma < I LOAD <.7A, C < T J C V LT76-. V IN = V, I LOAD = ma.6..8 V.V < V IN < V, ma < I LOAD < A, C T J C...7 V.V < V IN < V, ma < I LOAD <.7A, C < T J C...7 V LT76-. V IN =.8V, I LOAD = ma... V.V < V IN < V, ma < I LOAD < A, C T J C.8.. V.V < V IN < V, ma < I LOAD <.7A, C < T J C.8.. V ADJ Pin Voltage LT76 V IN =.V, I LOAD = ma.9..8 V (Notes, ).7V < V IN < V, ma < I LOAD < A, C T J C V.7V < V IN < V, ma < I LOAD <.7A, C < T J C V Line Regulation LT76-. V IN =.V to V, I LOAD = ma. mv LT76-.8 V IN =.V to V, I LOAD = ma mv LT76-. V IN = V to V, I LOAD = ma mv LT76-. V IN =.8V to V, I LOAD = ma. mv LT76 (Note ) V IN =.V to V, I LOAD = ma mv Load Regulation LT76-. V IN =.7V, I LOAD = ma to A 7 mv V IN =.7V, I LOAD = ma to A, C T J C mv V IN =.7V, I LOAD = ma to.7a, C < T J C mv LT76-.8 V IN =.8V, I LOAD = ma to A 8 mv V IN =.8V, I LOAD = ma to A, C T J C mv V IN =.8V, I LOAD = ma to.7a, C < T J C mv LT76-. V IN =.V, I LOAD = ma to A mv V IN =.V, I LOAD = ma to A, C T J C mv V IN =.V, I LOAD = ma to.7a, C < T J C mv LT76-. V IN =.V, I LOAD = ma to A mv V IN =.V, I LOAD = ma to A, C T J C mv V IN =.V, I LOAD = ma to.7a, C < T J C mv LT76 (Note ) V IN =.7V, I LOAD = ma to A mv V IN =.7V, I LOAD = ma to A, C T J C mv V IN =.7V, I LOAD = ma to.7a, C < T J C mv Dropout Voltage I LOAD = ma.. V V IN = V OUT(NOMINAL) I LOAD = ma. V (Notes, 6, ) I LOAD = ma.7. V I LOAD = ma.8 V I LOAD = ma.. V I LOAD = ma.7 V I LOAD =.A.. V I LOAD =.A. V I LOAD =.7A, C < T J C.66 V I LOAD = A.. V I LOAD = A, C T J C.66 V

4 ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are T A = C. (Note ) PARAMETER CONDITIONS MIN TYP MAX UNITS Pin Current I LOAD = ma. ma V IN = V OUT(NOMINAL) V I LOAD = ma..6 ma (Notes, 7) I LOAD = ma. ma I LOAD = ma 8 ma I LOAD =.A 7 ma I LOAD =.7A, C < T J C ma I LOAD = A, C T J C ma Output Voltage Noise C OUT = µf, I LOAD = A, BW = Hz to khz µv RMS ADJ Pin Bias Current (Notes, 8) µa Shutdown Threshold V OUT = Off to On.9 V V OUT = On to Off..7 V SHDN Pin Current V SHDN = V. µa (Note 9) V SHDN = V 7 µa Quiescent Current in Shutdown V IN = 6V, V SHDN = V. µa Ripple Rejection V IN V OUT =.V (Avg), V RIPPLE =.V P-P, 6 db f RIPPLE = Hz, I LOAD =.A Current Limit V IN = 7V, V OUT = V A LT76-.8, LT76-., LT76-. V IN = V OUT(NOMINAL) V, V OUT =.V, C T J C. A V IN = V OUT(NOMINAL) V, V OUT =.V, C < T J C.8 A LT76, LT76-. V IN =.7V, V OUT =.V, C T J C. A V IN =.7V, V OUT =.V, C < T J C.8 A Input Reverse Leakage Current V IN = V, V OUT = V ma Reverse Output Current (Note ) LT76-. V OUT =.V, V IN <.V 6 µa LT76-.8 V OUT =.8V, V IN <.8V 6 µa LT76-. V OUT =.V, V IN <.V 6 µa LT76-. V OUT =.V, V IN <.V 6 µa LT76 (Note ) V OUT =.V, V IN <.V 6 µa Note : Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note : The LT76 regulators are tested and specified under pulse load conditions such that T J T A. The LT76 is % tested at T A = C. Performance at C and C is assured by design, characterization and correlation with statistical process controls. Note : The LT76 (adjustable version) is tested and specified for these conditions with the ADJ pin connected to the OUT pin. Note. Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range must be limited. When operating at maximum output current, the input voltage range must be limited. Note : To satisfy requirements for minimum input voltage, the LT76 (adjustable version) is tested and specified for these conditions with an external resistor divider (two.k resistors) for an output voltage of.v. The external resistor divider will add a µa DC load on the output. Note 6: Dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. In dropout, the output voltage will be equal to: V IN V DROPOUT. Note 7: pin current is tested with V IN = V OUT(NOMINAL) V or V IN =.7V (whichever is greater) and a current source load. The pin current will decrease at higher input voltages. Note 8: ADJ pin bias current flows into the ADJ pin. Note 9: SHDN pin current flows into the SHDN pin. Note : Reverse output current is tested with the IN pin grounded and the OUT pin forced to the rated output voltage. This current flows into the OUT pin and out the pin. Note. For the LT76, LT76-. and LT76-.8 dropout voltage will be limited by the minimum input voltage specification under some output voltage/load conditions. Note. All combinations of absolute maximum input voltage and absolute maximum output voltage cannot be achieved. The absolute maximum differential from input to output is ±V. For example, with V IN = V, V OUT cannot be pulled below ground.

5 TYPICAL PERFOR A CE CHARACTERISTICS UW DROPOUT VOLTAGE (mv) Typical Dropout Voltage Guaranteed Dropout Voltage Dropout Voltage OUTPUT CURRENT (A) GUARANTEED DROPOUT VOLTAGE (mv) 7 = TEST POINTS 6 T J C T J C DROPOUT VOLTAGE (mv) 6 I L = A I L =.A I L =.A I L = ma I L = ma 7 OUTPUT CURRENT (A) 76 G 76 G 76 G QUIESCENT CURRENT (ma) Quiescent Current LT76-.8 Output Voltage LT76-. Output Voltage LT76-.8/./.. V IN = 6V R. L = I L = 7 LT76 OUTPUT VOLTAGE (V) I L = ma.76 7 OUTPUT VOLTAGE (V) I L = ma G 76 G 76 G6 OUTPUT VOLTAGE (V) LT76-. Output Voltage LT76 ADJ Pin Voltage LT76-.8 Quiescent Current I L = ma ADJ PIN VOLTAGE (V) I L = ma QUIESCENT CURRENT (ma) R L = G7 76 G8 76 G9

6 TYPICAL PERFOR A CE CHARACTERISTICS UW QUIESCENT CURRENT (ma) LT76-. Quiescent Current LT76-. Quiescent Current LT76 Quiescent Current R L = QUIESCENT CURRENT (ma) R L = QUIESCENT CURRENT (ma) R L =.k G 76 G 76 G LT76-.8 Pin Current LT76-. Pin Current LT76-. Pin Current PIN CURRENT (ma) R L =.6Ω I L = ma* R L = 8Ω I L = ma* *FOR V OUT =.8V R L = 6Ω I L = ma* PIN CURRENT (ma) R L = Ω I L = ma* R L = Ω I L = ma* *FOR V OUT =.V R L = 8.Ω I L = ma* PIN CURRENT (ma) *FOR V OUT =.V R L = 6.6Ω I L = ma* R L = Ω I L = ma* R L = Ω I L = ma* G 76 G 76 G LT76 Pin Current LT76-.8 Pin Current LT76-. Pin Current PIN CURRENT (ma) 9 6 *FOR V OUT =.V R L =.Ω I L = ma* R L =.Ω I L = ma* R L =.Ω I L = ma* PIN CURRENT (ma) 9 6 R L =.6Ω I L = A* R L =.Ω I L =.A* *FOR V OUT =.8V R L =.7Ω I L =.7A* PIN CURRENT (ma) 6 8 R L =.66Ω I L =.A* *FOR V OUT =.V R L =.8Ω I L = A* R L =.7Ω I L =.7A* G6 76 G7 76 G8 6

7 TYPICAL PERFOR A CE CHARACTERISTICS UW LT76-. Pin Current LT76 Pin Current Pin Current vs I LOAD PIN CURRENT (ma) 6 8 R L =.Ω I L = A* R L =.Ω I L =.A* *FOR V OUT =.V R L =.7Ω I L =.7A* PIN CURRENT (ma) 9 6 R L =.Ω I L = A* R L =.8Ω I L =.A* *FOR V OUT =.V R L =.7Ω I L =.7A* PIN CURRENT (ma) V IN = V OUT(NOM) V OUTPUT CURRENT (A). 76 G9 76 G 76 G SHDN Pin Threshold (On-to-Off) SHDN Pin Threshold (Off-to-On) SHDN Pin Input Current..9 I L = ma..9 9 SHDN PIN THRESHOLD (V) SHDN PIN THRESHOLD (V) I L = A I L = ma SHDN PIN INPUT CURRENT (µa) SHDN PIN VOLTAGE (V) 76 G 76 G 76 G SHDN Pin Input Current ADJ Pin Bias Current Current Limit SHDN PIN INPUT CURRENT (µa) V SHDN = V ADJ PIN BIAS CURRENT (µa) CURRENT LIMIT (A) 6 T J = C INPUT/OUTPUT DIFFERENTIAL (V) 76 G 76 G6 76 G7 7

8 TYPICAL PERFOR A CE CHARACTERISTICS UW Current Limit Reverse Output Current CURRENT LIMIT (A) 6 V IN = 7V V OUT = V 7 REVERSE OUTPUT CURRENT (ma) LT76 LT76-.8 LT76-. LT76-. V IN = V CURRENT FLOWS INTO OUTPUT PIN V OUT = V ADJ (LT76) V OUT = V FB (LT76-.8/-./-.) OUTPUT VOLTAGE (V) 76 G8 76 G9 REVERSE OUTPUT CURRENT (ma) Reverse Output Current V IN = V V OUT =.V (LT76) V OUT =.8V (LT76-.8) V OUT =.V (LT76-.) V OUT =.V (LT76-.) LT76-.8/-./-. LT G RIPPLE REJECTION (db) Ripple Rejection C OUT = µf TANTALUM µf CERAMIC C OUT = µf I L =.A TANTALUM V IN = V OUT(NOM) V mv RMS RIPPLE k k k M FREQUENCY (Hz) 76 G Ripple Rejection LT76 Minimum Input Voltage RIPPLE REJECTION (db) I L =.A V IN = V OUT(NOM) V.V P-P RIPPLE AT f = Hz MINIMUM I L = ma I L = A I L =.A I L = ma G 76 G 8

9 TYPICAL PERFOR A CE CHARACTERISTICS UW LOAD REGULATION (mv) Load Regulation LT76 LT76-.8 LT76-. LT76-. I L = ma TO A V IN =.7V (LT76) V IN = V OUT(NOM) V (LT76-.8/-./-.) 7 76 G OUTPUT NOISE SPECTRAL DENSITY (µv/ Hz).. Output Noise Spectral Density C OUT = µf I LOAD = A LT76-. LT76 LT76-. LT76-.8 k k k FREQUENCY (Hz) 76 G RMS Output Noise vs Load Current (Hz to khz) C OUT = µf LT76-. LT76-. Hz to khz Output Noise OUTPUT NOISE (µvrms) LT76-. LT76-.8 LT76 V OUT µv/ DIV.... LOAD CURRENT (A) C OUT = µf ms/div 76 G7 I L = A 76 G6 LT76-. Transient Response LT76-. Transient Response OUTPUT VOLTAGE DEVIATION (V) LOAD CURRENT (A) V IN =.V C IN =.µf TANTALUM C OUT = µf TANTALUM TIME (µs) OUTPUT VOLTAGE DEVIATION (V) LOAD CURRENT (A).... V IN =.V C IN = µf C OUT = µf TANTALUM µf CERAMIC TIME (µs) 76 G8 76 G9 9

10 PI FU CTIO S (DD and TO-/TSSOP) U U U SHDN (Pin /Pin ): Shutdown. The SHDN pin is used to put the LT76 regulators into a low power shutdown state. The output will be off when the SHDN pin is pulled low. The SHDN pin can be driven either by V logic or open-collector logic with a pull-up resistor. The pull-up resistor is required to supply the pull-up current of the open-collector gate, normally several microamperes, and the SHDN pin current, typically 7µA. If unused, the SHDN pin must be connected to V IN. The device will be in the low power shutdown state if the SHDN pin is not connected. IN (Pin /Pins,, ): Input. Power is supplied to the device through the IN pin. A bypass capacitor is required on this pin if the device is more than six inches away from the main input filter capacitor. In general, the output impedance of a battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of µf to µf is sufficient. The LT76 regulators are designed to withstand reverse voltages on the IN pin with respect to ground and the OUT pin. In the case of a reverse input, which can happen if a battery is plugged in backwards, the device will act as if there is a diode in series with its input. There will be no reverse current flow into the regulator and no reverse voltage will appear at the load. The device will protect both itself and the load. (Pin /Pins, 7, 8, 9, 6, 7): Ground. The exposed pad (FE Package) is ground and must be soldered to the PCB for rated thermal performance. OUT (Pin /Pins,, ): Output. The output supplies power to the load. A minimum output capacitor of µf is required to prevent oscillations. Larger output capacitors will be required for applications with large transient loads to limit peak voltage transients. See the Applications Information section for more information on output capacitance and reverse output characteristics. SENSE (Pin /Pin 6): Sense. For fixed voltage versions of the LT76 (LT76-.8/LT76-./LT76-.), the SENSE pin is the input to the error amplifier. Optimum regulation will be obtained at the point where the SENSE pin is connected to the OUT pin of the regulator. In critical applications, small voltage drops are caused by the resistance (R P ) of PC traces between the regulator and the load. These may be eliminated by connecting the SENSE pin to the output at the load as shown in Figure (Kelvin Sense Connection). Note that the voltage drop across the external PC traces will add to the dropout voltage of the regulator. The SENSE pin bias current is 6µA at the nominal rated output voltage. The SENSE pin can be pulled below ground (as in a dual supply system where the regulator load is returned to a negative supply) and still allow the device to start and operate. ADJ (Pin /Pin 6): Adjust. For the adjustable LT76, this is the input to the error amplifier. This pin is internally clamped to ±7V. It has a bias current of µa which flows into the pin. The ADJ pin voltage is.v referenced to ground and the output voltage range is.v to V. IN OUT R P V IN LT76 SHDN SENSE LOAD R P 76 F Figure. Kelvin Sense Connection

11 APPLICATIO S I FOR ATIO The LT76 series are A low dropout regulators optimized for fast transient response. The devices are capable of supplying A at a dropout voltage of mv. The low operating quiescent current (ma) drops to less than µa in shutdown. In addition to the low quiescent current, the LT76 regulators incorporate several protection features which make them ideal for use in battery-powered systems. The devices are protected against both reverse input and reverse output voltages. In battery backup applications where the output can be held up by a backup battery when the input is pulled to ground, the LT76-X acts like it has a diode in series with its output and prevents reverse current flow. Additionally, in dual supply applications where the regulator load is returned to a negative supply, the output can be pulled below ground by as much as V and still allow the device to start and operate. Adjustable Operation The adjustable version of the LT76 has an output voltage range of.v to V. The output voltage is set by the ratio of two external resistors as shown in Figure. The device servos the output to maintain the voltage at the ADJ pin at.v referenced to ground. The current in R is then equal to.v/r and the current in R is the current in R plus the ADJ pin bias current. The ADJ pin bias current, µa at C, flows through R into the ADJ pin. The output voltage can be calculated using the formula in Figure. The value of R should be less than.7k to minimize errors in the output voltage caused by the ADJ pin bias current. Note that in shutdown the output is turned off and the divider current will be zero. The adjustable device is tested and specified with the ADJ pin tied to the OUT pin for an output voltage of.v. Specifications for output voltages greater than.v will V IN IN LT76 OUT ADJ U W U U R R 76 F V OUT Figure. Adjustable Operation R VOUT =. V ( IADJ)( R) R VADJ =. V IADJ = µ AAT C OUTPUT RANGE =.V TO V be proportional to the ratio of the desired output voltage to.v: V OUT /.V. For example, load regulation for an output current change of ma to A is mv typical at V OUT =.V. At V OUT = V, load regulation is: (V/.V)( mv) =.mv Output Capacitance and Transient Response The LT76 regulators are designed to be stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of µf with an ESR in the range of mω to Ω is recommended to prevent oscillations. Larger values of output capacitance can decrease the peak deviations and provide improved transient response for larger load current changes. Bypass capacitors, used to decouple individual components powered by the LT76-X, will increase the effective output capacitor value. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics used are specified with EIA temperature characteristic codes of ZU, YV, XR and X7R. The ZU and YV dielectrics are good for providing high capacitances in a small package, but they tend to have strong voltage and temperature coefficients as shown in Figures and. When used with a V regulator, a 6V µf YV capacitor can exhibit an effective value as low as µf to µf for the DC bias voltage applied and over the operating temperature range. The XR and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the XR is less expensive and is available in higher values. Care still must be exercised when using XR and X7R capacitors; the XR and X7R codes only specify operating temperature range and maximum capacitance change over temperature. Capacitance change due to DC bias with XR and X7R capacitors is better than YV and ZU capacitors, but can still be significant enough to drop capacitor values below appropriate levels. Capacitor DC bias characteristics tend to improve as component case size increases, but expected capacitance at operating voltage should be verified.

12 APPLICATIO S I FOR ATIO Figure. Ceramic Capacitor Temperature Characteristics CHANGE IN VALUE (%) CHANGE IN VALUE (%) U W U U BOTH CAPACITORS ARE 6V, CASE SIZE, µf 6 8 DC BIAS VOLTAGE (V) Figure. Ceramic Capacitor DC Bias Characteristics YV XR 76 F 8 BOTH CAPACITORS ARE 6V, CASE SIZE, µf 7 76 F Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. Overload Recovery Like many IC power regulators, the LT76-X has safe operating area protection. The safe area protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. XR YV 6 The protection is designed to provide some output current at all values of input-to-output voltage up to the device breakdown. When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start up into very heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output currents. With a high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. Other regulators, such as the LT8, also exhibit this phenomenon, so it is not unique to the LT76 series. The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations are immediately after the removal of a short circuit or when the SHDN pin is pulled high after the input voltage has already been turned on. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable output operating points for the regulator. With this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. Output Voltage Noise The LT76 regulators have been designed to provide low output voltage noise over the Hz to khz bandwidth while operating at full load. Output voltage noise is typically nv Hz over this frequency bandwidth for the LT76 (adjustable version). For higher output voltages (generated by using a resistor divider), the output voltage noise will be gained up accordingly. This results in RMS noise over the Hz to khz bandwidth of µv RMS for the LT76 increasing to 7µV RMS for the LT76-.. Higher values of output voltage noise may be measured when care is not exercised with regards to circuit layout and testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the LT76-X. Power supply ripple rejection must also be considered; the LT76 regulators do not have unlimited power supply rejection and will pass a small portion of the input noise through to the output.

13 APPLICATIONS INFORMATION Thermal Considerations U W U U The power handling capability of the device is limited by the maximum rated junction temperature ( C). The power dissipated by the device is made up of two components:. Output current multiplied by the input/output voltage differential: (I OUT )(V IN V OUT ), and. pin current multiplied by the input voltage: (I )(V IN ). The pin current can be found using the Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. The LT76 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum junction temperature rating of C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered. For surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Surface mount heatsinks and plated through-holes can also be used to spread the heat generated by power devices. The following tables list thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on /6" FR- board with one ounce copper. Table. Q Package, -Lead DD COPPER AREA THERMAL RESISTANCE TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) mm mm mm C/W mm mm mm C/W mm mm mm C/W * Device is mounted on topside Table. FE Package, 6-Lead TSSOP COPPER AREA THERMAL RESISTANCE TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) mm mm mm 8 C/W mm mm mm C/W mm mm mm 8 C/W mm mm mm 6 C/W * Device is mounted on topside T Package, -Lead TO- Thermal Resistance (Junction-to-Case) =. C/W Calculating Junction Temperature Example: Given an output voltage of.v, an input voltage range of V to 6V, an output current range of ma to ma and a maximum ambient temperature of C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: I OUT(MAX) (V IN(MAX) V OUT ) I (V IN(MAX) ) where, I OUT(MAX) = ma V IN(MAX) = 6V I at (I OUT = ma, V IN = 6V) = ma So, P = ma(6v.v) ma(6v) =.W Using a DD package, the thermal resistance will be in the range of C/W to C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to:.w(8 C/W) = 9. C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: T JMAX = C 9. C = 89. C

14 APPLICATIONS INFORMATION U W U U Protection Features The LT76 regulators incorporate several protection features which make them ideal for use in battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the devices are protected against reverse input voltages, reverse output voltages and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature should not exceed C. The input of the device will withstand reverse voltages of V. Current flow into the device will be limited to less than ma and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries which can be plugged in backward. The output of the LT76-X can be pulled below ground without damaging the device. If the input is left open circuit or grounded, the output can be pulled below ground by V. For fixed voltage versions, the output will act like a large resistor, typically k or higher, limiting current flow to typically less than 6µA. For adjustable versions, the output will act like an open circuit; no current will flow out of the pin. If the input is powered by a voltage source, the output will source the short-circuit current of the device and will protect itself by thermal limiting. In this case, grounding the SHDN pin will turn off the device and stop the output from sourcing the short-circuit current. The ADJ pin of the adjustable device can be pulled above or below ground by as much as 7V without damaging the device. If the input is left open circuit or grounded, the ADJ pin will act like an open circuit when pulled below ground and like a large resistor (typically k) in series with a diode when pulled above ground. In situations where the ADJ pin is connected to a resistor divider that would pull the ADJ pin above its 7V clamp voltage if the output is pulled high, the ADJ pin input current must be limited to less than ma. For example, a resistor divider is used to provide a regulated.v output from the.v reference when the output is forced to V. The top resistor of the resistor divider must be chosen to limit the current into the ADJ pin to less than ma when the ADJ pin is at 7V. The V difference between OUT and ADJ pins divided by the ma maximum current into the ADJ pin yields a minimum top resistor value of.6k. In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left open circuit. Current flow back into the output will follow the curve shown in Figure. When the IN pin of the LT76-X is forced below the OUT pin or the OUT pin is pulled above the IN pin, input current will typically drop to less than µa. This can happen if the input of the device is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or a second regulator circuit. The state of the SHDN pin will have no effect on the reverse output current when the output is pulled above the input. REVERSE OUTPUT CURRENT (ma) LT76 LT76-.8 LT76-. LT OUTPUT VOLTAGE (V) Figure. Reverse Output Current 76 F V IN = OV CURRENT FLOWS INTO OUTPUT PIN V OUT = V ADJ (LT76) V OUT = V FB (LT76-.8, LT76-., LT76-.)

15 TYPICAL APPLICATIO S U SCR Preregulator Provides Efficiency Over Line Variations 9V AC TO V AC L V AC AT V IN V AC AT V IN NTE7 N8 k L µh µf k* LT76-. IN OUT SHDN FB µf V OUT.V A NTE7.k* N N SYNC V TO ALL V POINTS N µf.k 7Ω CA / LT8 N8 k.µf V L: COILTRONICS CTX-- L: STANCOR P-86 *% FILM RESISTOR.µF 7Ω CB / LT8 V N8 k µf V A LT6 k k V LT.V 76 TA

16 TYPICAL APPLICATIO S U Adjustable Current Source V IN >.7V C µf R k LT-. R.k R.Ω R.k R6.k IN LT76-.8 SHDN FB OUT R8 k LOAD R k C µf R7 7Ω ADJUST R FOR A TO A CONSTANT CURRENT C.µF 8 / LT66 76 TA 6

17 PACKAGE DESCRIPTION U Q Package -Lead Plastic DD Pak (LTC DWG # -8-6).6 (6.).6 (.).6 (.) TYP.9. (9.96.) TYP.6.8 (.9.7).. (..97).6 (.).8 (.68)..7 ( ).9 (.99) TYP..8. (... ). (7.6).7 (.9) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK... (.6..8 ).67 (.7).8.8 BSC (.7.96) TYP.. (..8).9. (..9). ±. (.7 ±.) Q(DD) RECOMMENDED SOLDER PAD LAYOUT NOTE:. DIMENSIONS IN INCH/(MILLIMETER). DRAWING NOT TO SCALE RECOMMENDED SOLDER PAD LAYOUT FOR THICKER SOLDER PASTE APPLICATIONS 7

18 PACKAGE DESCRIPTION U T Package -Lead Plastic TO- (Standard) (LTC DWG # -8-).9. (9.96.).7. (.7.97) DIA.6.8 (.9.7).. (..97)..7 ( ).6. (.68.7)..7 ( ).7.6 (.78.78).6 (.7) TYP.7.78 ( ) SEATING PLANE.. (.86.).6. (6.6 8.).9. (..9)..9* (.97.9) BSC.67 (.7).8.8 (.7.96)..6 (.9.9).. (..8) * MEASURED AT THE SEATING PLANE T (TO-) 99 8

19 PACKAGE DESCRIPTION U FE Package 6-Lead Plastic TSSOP (.mm) (Reference LTC DWG # -8-66) Exposed Pad Variation BB.8 (.).9.* (.9.).8 (.) ±.. ±..9 (.6) SEE NOTE. ±.. ±..9 (.6) 6. (.) BSC.6 BSC RECOMMENDED SOLDER PAD LAYOUT..* (.69.77). REF (.) MAX.9. (..79)..7 (..) NOTE:. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS. DIMENSIONS ARE IN (INCHES). DRAWING NOT TO SCALE.6 (.6) BSC.9. (.77.8) TYP. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED.mm (.6") PER SIDE.. (..6) FE6 (BB) TSSOP Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 9

20 TYPICAL APPLICATIO U Paralleling of Regulators for Higher Output Current V IN >.7V C µf R.Ω IN OUT LT76-. SHDN FB C µf.v 6A SHDN R.Ω IN OUT LT76 SHDN ADJ R6 6.6k R7.k R.k R.k 8 / LT66 C.µF R k 76 TA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT ma Low Dropout Regulator with µa I Q Includes.V Reference and Comparator LT ma Micropower Low Dropout Regulator µa I Q, SOT- Package LT9 7mA Micropower Low Dropout Regulator µa Quiescent Current LT7 ma Negative Low Dropout Micropower Regulator µa I Q,.6V Dropout Voltage, SOT- Package LT7.A, khz Step-Down Converter.A,.7Ω Internal Switch, SO-8 Package LT ma Low Dropout Micropower Regulator with Shutdown µa I Q, Reverse Battery Protection LT9 A Low Dropout Regulator with µa I Q mv Dropout Voltage LT7 UltraFast TM Transient Response Low Dropout Regulator Drives External PNP LT7 UltraFast Transient Response Low Dropout Regulator Drives External N-Channel MOSFET LT7 Synchronous Step-Down Converter High Efficiency, OPTI-LOOP Compensation LT76 Series ma, Low Noise, Low Dropout Micropower Regulators in SOT- µa Quiescent Current, µv RMS Noise, SOT- Package LT76 Series ma, Low Noise, LDO Micropower Regulators µa Quiescent Current, µv RMS Noise, MSOP Package LT76 Series ma, Low Noise, LDO Micropower Regulators µa Quiescent Current, µv RMS Noise, SO-8 Package LT96 ma, Low Noise, LDO Micropower Regulator µv RMS Noise, MSOP Package LT96.A, Low Noise, Fast Transient Response LDO µv RMS Noise, SOT- Package UltraFast is a trademark of Linear Technology Corporation. OPTI-LOOP is a registered trademark of Linear Technology Corporation. Linear Technology Corporation 6 McCarthy Blvd., Milpitas, CA 9-77 (8) -9 FAX: (8) -7 LT REV B PRINTED IN USA LINEAR TECHNOLOGY CORPORATION