LT1121/LT1121-3.3/LT1121-5 Micropower Low Dropout Regulators with Shutdown U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT1121/LT1121-3.3/LT1121-5 are micropower low dropout regulators with shutdown. These devices are capable of supplying 150mA of output current with a dropout voltage of 0.4V. Designed for use in batterypowered systems, the low quiescent current, 30µA operating and 16µA in shutdown, makes them an ideal choice. The quiescent current is well-controlled; it does not rise in dropout as it does with many other low dropout PNP regulators. 0.4V Dropout Voltage 150mA Output Current 30µA Quiescent Current No Protection Diodes Needed Adjustable Output from 3.8V to 20V 3.3V and 5V Fixed Output Voltages Controlled Quiescent Current in Dropout Shutdown 16µA Quiescent Current in Shutdown Stable with 0.33µF Output Capacitor Reverse Battery Protection No Reverse Current with Input Low Thermal Limiting Other features of the LT1121/LT1121-3.3/LT1121-5 include the ability to operate with very small output capacitors. They are stable with only 0.33µF on the output while most older devices require between 1µF and 100µF for stability. Small ceramic capacitors can be used, enhancing manufacturability. Also the input may be connected to ground or a reverse voltage without reverse current flow from output to input. This makes the LT1121 series ideal for backup power situations where the output is held high and the input is at ground or reversed. Under these conditions only 16µA will flow from the output pin to ground. UO APPLICATI ■ ■ Low Current Regulator Regulator for Battery-Powered Systems Post Regulator for Switching Supplies UO ■ S TYPICAL APPLICATI Dropout Voltage 5V Battery-Powered Supply with Shutdown 0.5 IN OUT 1 LT1121-3.3 5V 5 3.3V OUT 150mA + 0.4 1µF SOLID TANTALUM SHDN GND 3 VSHDN (PIN 5) OUTPUT < 0.25 OFF > 2.8 ON NC ON DROPOUT VOLTAGE (V) 8 0.3 0.2 0.1 LT1121 • TA01 0 0 20 40 60 80 100 120 140 160 OUTPUT CURRENT (mA) LT1121 • TA02 1 LT1121/LT1121-3.3/LT1121-5 W W W AXI U U ABSOLUTE RATI GS Input Voltage ...................................................... ±30V* Output Pin Reverse Current ................................. 10mA Adjust Pin Current ............................................... 10mA Shutdown Pin Input Voltage (Note 1) ........ 6.5V, – 0.6V Shutdown Pin Input Current (Note 1) .................. 20mA Output Short-Circuit Duration ......................... Indefinite Storage Temperature Range ................. – 65°C to 150°C Operating Junction Temperature Range (Note 2) LT1121C-X ......................................... 0°C to 125°C LT1121I-X ..................................... – 40°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C *For applications requiring input voltage ratings greater than 30V, contact the factory. W U U PACKAGE/ORDER I FOR ATIO TOP VIEW OUT 1 8 IN NC/ADJ* 2 7 NC** GND 3 6 NC** NC 4 5 SHDN N8 PACKAGE 8-LEAD PLASTIC DIP S8 PACKAGE 8-LEAD PLASTIC SOIC * PIN 2 = NC FOR LT1121-3.3/LT1121-5 = ADJ FOR LT1121 ** PINS 6 AND 7 ARE FLOATING (NO INTERNAL CONNECTION) ON THE STANDARD S8 PACKAGE. PINS 6 AND 7 CONNECTED TO GROUND ON THE A VERSION OF THE LT1121 (S8 ONLY). CONNECTING PINS 6 AND 7 TO THE GROUND PLANE WILL REDUCE THERMAL RESISTANCE. SEE THERMAL RESISTANCE TABLES IN THE APPLICATIONS INFORMATION SECTION. θJA ≈ 120°C/ W (N8, S8) θJA ≈ 70°C/ W (AS8) ORDER PART NUMBER LT1121CN8 LT1121CN8-3.3 LT1121CN8-5 LT1121IN8 LT1121IN8-3.3 LT1121IN8-5 LT1121CS8 LT1121CS8-3.3 LT1121CS8-5 LT1121IS8 LT1121IS8-3.3 LT1121IS8-5 LT1121ACS8 LT1121ACS8-3.3 LT1121ACS8-5 LT1121AIS8 LT1121AIS8-3.3 LT1121AIS8-5 S8 PART MARKING 1121 11213 11215 1121I 121I3 121I5 1121A 121A3 121A5 121AI 121AI3 121AI5 BOTTOM VIEW FRONT VIEW TAB IS GND 3 OUTPUT 2 GND 1 VIN 3 2 1 IN GND OUT Z PACKAGE 3-LEAD PLASTIC TO-92 ST PACKAGE 3-LEAD PLASTIC SOT-223 LT1121 • PO03 LT1121 • PO02 θJA ≈ 50°C/ W θJA ≈ 150°C/ W ORDER PART NUMBER ORDER PART NUMBER LT1121CST-3.3 LT1121IST-3.3 LT1121CST-5 LT1121IST-5 LT1121CZ-3.3 LT1121IZ-3.3 LT1121CZ-5 LT1121IZ-5 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS PARAMETER Regulated Output Voltage (Note 3) CONDITIONS LT1121-3.3 LT1121-5 LT1121 (Note 4) Line Regulation 2 LT1121-3.3 LT1121-5 LT1121 (Note 4) VIN = 3.8V, IOUT = 1mA, TJ = 25°C 4.3V < VIN < 20V, 1mA < IOUT < 150mA VIN = 5.5V, IOUT = 1mA, TJ = 25°C 6V < VIN < 20V, 1mA < IOUT < 150mA VIN = 4.3V, IOUT = 1mA, TJ = 25°C 4.8V < VIN < 20V, 1mA < IOUT < 150mA ∆VIN = 4.8V to 20V, IOUT = 1mA ∆VIN = 5.5V to 20V, IOUT = 1mA ∆VIN = 4.3V to 20V, IOUT = 1mA ● ● ● ● ● ● MIN 3.250 3.200 4.925 4.850 3.695 3.640 TYP 3.300 3.300 5.000 5.000 3.750 3.750 1.5 1.5 1.5 MAX 3.350 3.400 5.075 5.150 3.805 3.860 10 10 10 UNITS V V V V V V mV mV mV LT1121/LT1121-3.3/LT1121-5 ELECTRICAL CHARACTERISTICS PARAMETER Load Regulation Dropout Voltage (Note 5) Ground Pin Current (Note 6) Adjust Pin Bias Current (Notes 4, 7) Shutdown Threshold Shutdown Pin Current (Note 8) Quiescent Current in Shutdown (Note 9) Ripple Rejection Current Limit Input Reverse Leakage Current Reverse Output Current (Note 10) CONDITIONS LT1121-3.3 MIN ∆ILOAD = 1mA to 150mA, TJ = 25°C ∆ILOAD = 1mA to 150mA LT1121-5 ∆ILOAD = 1mA to 150mA, TJ = 25°C ∆ILOAD = 1mA to 150mA LT1121 (Note 4) ∆ILOAD = 1mA to 150mA, TJ = 25°C ∆ILOAD = 1mA to 150mA ILOAD = 1mA, TJ = 25°C ILOAD = 1mA ILOAD = 50mA, TJ = 25°C LOAD = 50mA ILOAD = 100mA, TJ = 25°C ILOAD = 100mA ILOAD = 150mA, TJ = 25°C ILOAD = 150mA ILOAD = 0mA ILOAD = 1mA ILOAD = 10mA ILOAD = 50mA ILOAD = 100mA ILOAD = 150mA TJ = 25°C VOUT = Off to On VOUT = On to Off VSHDN = 0V VIN = 6V, VSHDN = 0V VIN – VOUT = 1V (Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 0.1A VIN – VOUT = 7V, TJ = 25°C VIN = –20V, VOUT = 0V LT1121-3.3 VOUT = 3.3V, VIN = 0V LT1121-5 VOUT = 5V, VIN = 0V LT1121 (Note 4) VOUT = 3.8V, VIN = 0V The ● denotes specifications which apply over the operating temperature range. Note 1: The Shutdown pin input voltage rating is required for a low impedance source. Internal protection devices connected to the shutdown pin will turn on and clamp the pin to approximately 7V or – 0.6V. This range allows the use of 5V logic devices to drive the pin directly. For high impedance sources or logic running on supply voltages greater than 5.5V, the maximum current driven into the shutdown pin must be limited to less than 20mA. Note 2: For junction temperatures greater than 110°C, a minimum load of 1mA is recommended. For TJ > 110°C and IOUT < 1mA, output voltage may increase by 1%. Note 3: 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. ● ● ● TYP – 12 – 20 – 17 – 28 – 12 – 18 0.13 ● 0.30 ● 0.37 ● 0.42 ● ● ● ● ● ● ● ● ● 0.25 ● ● 50 30 90 350 1.5 4.0 7.0 150 1.2 0.75 6 15 58 200 ● 16 16 16 MAX – 20 – 30 – 30 – 45 – 20 – 30 0.16 0.25 0.35 0.50 0.45 0.60 0.55 0.70 50 120 500 2.5 7.0 14.0 300 2.8 10 22 500 1.0 25 25 25 UNITS mV mV mV mV mV mV V V V V V V V V µA µA µA mA mA mA nA V V µA µA dB mA mA µA µA µA Note 4: The LT1121 (adjustable version) is tested and specified with the adjust pin connected to the output pin. Note 5: Dropout voltage is the minimum input/output voltage required to maintain regulation at the specified output current. In dropout the output voltage will be equal to: (VIN – VDROPOUT). Note 6: Ground pin current is tested with VIN = VOUT (nominal) and a current source load. This means that the device is tested while operating in its dropout region. This is the worst case ground pin current. The ground pin current will decrease slightly at higher input voltages. Note 7: Adjust pin bias current flows into the adjust pin. Note 8: Shutdown pin current at VSHDN = 0V flows out of the shutdown pin. Note 9: Quiescent current in shutdown is equal to the sum total of the shutdown pin current (6µA) and the ground pin current (9µA). Note 10: Reverse output current is tested with the input pin grounded and the output pin forced to the rated output voltage. This current flows into the output pin and out of the ground pin. 3 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS 0.6 TJ ≤ 125°C 0.5 TJ ≤ 25°C 0.3 0.2 0.1 10 ILOAD = 150mA QUIESCENT CURRENT (µA) 0.6 0.4 Quiescent Current Dropout Voltage 0.7 DROPOUT VOLTAGE (V) DROPOUT VOLTAGE (V) Guaranteed Dropout Voltage 0.7 ILLOAD = 100mA 0.5 0.4 0.3 ILOAD = 50mA 0.2 ILOAD = 1mA VIN = 6V RLOAD = ∞ 40 VSHDN =OPEN 30 20 VSHDN =0V 10 0.1 = TEST POINTS 0 0 0 –50 40 60 80 100 120 140 160 OUTPUT CURRENT (mA) 20 50 25 0 75 TEMPERATURE (°C) –25 1121 G27 100 80 VSHDN = OPEN 60 40 20 120 TJ = 25°C RLOAD = ∞ 80 VSHDN = OPEN 60 40 20 VSHDN = 0V 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 1 0 10 2 3 4 5 6 7 INPUT VOLTAGE (V) 80 VSHDN = OPEN 60 40 20 VSHDN = 0V 0 0 0 8 9 10 3.38 5.04 3.79 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G22 4 OUTPUT VOLTAGE (V) 3.34 OUTPUT VOLTAGE (V) 3.81 –25 10 IOUT = 1mA 5.06 3.22 –50 9 8 3.83 3.36 3.24 3 4 5 6 7 INPUT VOLTAGE (V) LT1121 Adjust Pin Voltage IOUT = 1mA 3.26 2 1121 G03 5.08 IOUT = 1mA 3.28 1 0 LT1121-5 Output Voltage LT1121-3.3 Output Voltage 3.30 VSHDN = 0V 1121 G02 1121 G04 3.32 TJ = 25°C RLOAD = ∞ VOUT = VADJ 100 QUIESCENT CURRENT (µA) TJ = 25°C RLOAD = ∞ QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) LT1121 Quiescent Current 120 120 125 100 1121 G11 LT1121-5 Quiescent Current 100 50 0 75 25 TEMPERATURE (°C) 1121 G14 LT1121-3.3 Quiescent Current OUTPUT VOLTAGE (V) 0 –50 –25 125 100 5.02 5.00 4.98 3.77 3.75 3.73 4.96 3.71 4.94 3.69 4.92 –50 –25 50 0 75 25 TEMPERATURE (°C) 100 125 1121 G23 3.67 –50 –25 50 0 75 25 TEMPERATURE (°C) 100 125 1121 G24 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS LT1121-3.3 Ground Pin Current 800 800 800 TJ = 25°C TJ = 25°C 700 GROUND PIN CURRENT (µA) RLOAD = 130Ω ILOAD = 25mA* 600 500 RLOAD = 330Ω ILOAD = 10mA* 400 300 *FOR VOUT = 3.3V 200 RLOAD = 3.3k ILOAD = 1mA* 100 600 500 RLOAD = 500Ω ILOAD = 10mA* 400 300 *FOR VOUT = 5V 200 RLOAD = 5k ILOAD = 1mA* 100 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 1121 G10 4 3 RLOAD = 66Ω ILOAD = 50mA* 2 1 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 RLOAD = 33Ω ILOAD = 150mA* 7 6 RLOAD = 50Ω ILOAD = 100mA* 5 4 3 RLOAD = 100Ω ILOAD = 50mA* 2 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 4 2 9 0 20 6 5 40 60 80 100 120 140 160 OUTPUT CURRENT (mA) 1121 G29 10 RLOAD = 38Ω ILOAD = 100mA* 4 3 RLOAD = 75Ω ILOAD = 50mA* 2 10 *FOR VOUT = 3.75V 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 10 9 1121 G07 2.0 ILOAD = 1mA 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0 –50 8 Shutdown Pin Threshold (Off-to-On) 1.6 ILOAD = 150mA 1.4 1.2 ILOAD = 1mA 1.0 0.8 0.6 0.4 0.2 0.2 0 9 RLOAD = 25Ω ILOAD = 150mA* 7 0 8 SHUTDOWN THRESHOLD (V) TJ = –55°C SHUTDOWN THRESHOLD (V) GROUND PIN CURRENT (mA) 1.8 TJ = 25°C 8 TJ = 25°C VOUT = VADJ 1 *FOR VOUT = 5V 2.0 6 3 4 5 6 7 INPUT VOLTAGE (V) 8 Shutdown Pin Threshold (On-to-Off) 14 8 2 1121 G05 Ground Pin Current 10 1 1121 G08 9 8 0 10 VIN = 3.3V (LT1121-3.3) VIN = 5V (LT1121-5) VIN = 3.75V (LT1121) DEVICE IS OPERATING IN DROPOUT TJ = 125°C RLOAD = 3.8k ILOAD = 1mA* LT1121 Ground Pin Current 1121 G09 12 *FOR VOUT = 3.75V 200 10 1 *FOR VOUT = 3.3V 0 300 0 GROUND PIN CURRENT (mA) RLOAD = 33Ω ILOAD = 100mA* 5 GROUND PIN CURRENT (mA) GROUND PIN CURRENT (mA) RLOAD = 22Ω ILOAD = 150mA* RLOAD = 380Ω ILOAD = 10mA* 400 0 10 TJ = 25°C 9 6 0 9 10 TJ = 25°C 7 500 LT1121-5 Ground Pin Current 10 8 600 1121 G06 LT1121-3.3 Ground Pin Current 9 RLOAD = 150Ω ILOAD = 25mA* 100 0 0 TJ = 25°C VOUT = VADJ 700 RLOAD = 200Ω ILOAD = 25mA* GROUND PIN CURRENT (µA) 700 GROUND PIN CURRENT (µA) LT1121 Ground Pin Current LT1121-5 Ground Pin Current –25 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G16 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G17 5 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS 10 7 6 5 4 3 2 1 50 25 0 75 TEMPERATURE (°C) –25 20 15 10 5 0 1 7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V) 1121 G15 10 5 350 350 300 300 250 200 150 100 0 125 100 Reverse Output Current 1 4 2 5 3 INPUT VOLTAGE (V) 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) –25 50 0 75 25 TEMPERATURE (°C) 100 125 VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz IOUT = 100mA IOUT = 100mA VIN = 6V + 50mVRMS RIPPLE 90 80 60 58 56 54 COUT = 47µF SOLID TANTALUM 70 60 50 40 30 COUT = 1µF SOLID TANTALUM 20 10 9 10 1121 G01 6 100 Ripple Rejection 52 LT1121-5 0 150 1121 G19 RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) OUTPUT PIN CURRENT (µA) 20 10 200 100 62 LT1121-3.3 125 250 Ripple Rejection 40 100 VIN = 7V VOUT = 0V 0 –50 7 6 64 LT1121 (VOUT = VADJ) 50 0 75 25 TEMPERATURE (°C) 1121 G20 100 TJ = 25°C 90 VIN = 0V CURRENT FLOWS 80 INTO OUTPUT PIN 70 –25 50 1121 G13 30 50 Current Limit 0 50 100 400 50 60 150 1121 G25 CURRENT LIMIT (mA) SHORT-CIRCUIT CURRENT (mA) OUTPUT PIN CURRENT (µA) 15 50 25 0 75 TEMPERATURE (°C) 200 VOUT = 0V VIN = 0V VOUT = 5V (LT1121-5) VOUT = 3.3V (LT1121-3.3) VOUT = 3.8V (LT1121) 20 0 9 400 –25 250 Current Limit Reverse Output Current 0 –50 300 1121 G28 30 25 350 0 –50 0 125 100 ADJUST PIN BIAS CURRENT (nA) SHUTDOWN PIN INPUT CURRENT (mA) SHUTDOWN PIN CURRENT (µA) 8 0 –50 400 25 VSHDN = 0V 9 LT1121 Adjust Pin Bias Current Shutdown Pin Input Current Shutdown Pin Current 50 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G18 0 10 100 1k 10k FREQUENCY (Hz) 100k 1M 1121 G26 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS LT1121-5 Load Transient Response LT1121-5 Load Transient Response Load Regulation 0 OUTPUT VOLTAGE DEVIATION (V) LT1121-3.3 –15 –20 0.1 VIN = 6V CIN = 0.1µF COUT = 1µF 0 –0.1 –0.2 0.2 0.1 VIN = 6V CIN = 0.1µF COUT = 3.3µF 0 –0.1 –0.2 LT1121-5 –30 –35 * ADJ PIN TIED TO OUTPUT PIN –40 –50 –25 50 0 75 25 TEMPERATURE (°C) 100 125 LOAD CURRENT (mA) –25 LOAD CURRENT (mA) LOAD REGULATION (mV) LT1121* –10 0.2 OUTPUT VOLTAGE DEVIATION (V) ∆ILOAD = 1mA TO 150mA –5 150 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms) 1121 G21 1121 G30 150 100 50 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms) 1121 G31 U U U PI FU CTIO S Input Pin: Power is supplied to the device through the input pin. The input pin should be bypassed to ground if the device is more than 6 inches away from the main input filter capacitor. In general the output impedance of a battery rises with frequency so it is usually adviseable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 0.1µF to 1µF is sufficient. The LT1121 is designed to withstand reverse voltages on the input pin with respect to both ground and the output pin. In the case of a reversed input, which can happen if a battery is plugged in backwards, the LT1121 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1121 and no reverse voltage will appear at the load. The device will protect both itself and the load. Output Pin: The output pin supplies power to the load. An output capacitor is required to prevent oscillations. See the Applications Information section for recommended value of output capacitance and information on reverse output characteristics. Shutdown Pin: This pin is used to put the device into shutdown. In shutdown the output of the device is turned off. This pin is active low. The device will be shut down if the shutdown pin is pulled low. The shutdown pin current with the pin pulled to ground will be 6µA. The shutdown pin is internally clamped to 7V and – 0.6V (one VBE). This allows the shutdown pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor. The pullup resistor is only required to supply the leakage current of the open collector gate, normally several microamperes. Pull-up current must be limited to a maximum of 20mA. A curve of shutdown pin input current as a function of voltage appears in the Typical Performance Characteristics. If the shutdown pin is not used it can be left open circuit. The device will be active, output on, if the shutdown pin is not connected. Adjust Pin: For the adjustable LT1121, the adjust pin is the input to the error amplifier. This pin is internally clamped to 6V and – 0.6V (one VBE). It has a bias current of 150nA which flows into the pin. See Bias Current curve in the Typical Performance Characteristics. The adjust pin reference voltage is 3.75V referenced to ground. The output voltage range that can be produced by this device is 3.75V to 30V. 7 LT1121/LT1121-3.3/LT1121-5 W U U UO APPLICATI S I FOR ATIO The LT1121 is a micropower low dropout regulator with shutdown, capable of supplying up to 150mA of output current at a dropout voltage of 0.4V. The device operates with very low quiescent current (30µA). In shutdown the quiescent current drops to only 16µA. In addition to the low quiescent current the LT1121 incorporates several protection features which make it ideal for use in batterypowered systems. The device is protected against both reverse input voltages 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 LT1121 acts like it has a diode in series with its output and prevents reverse current flow. approximately 15ppm/°C. The adjust pin bias current has a negative temperature coefficient. These effects are small and will tend to cancel each other. Adjustable Operation Thermal Considerations The adjustable version of the LT1121 has an output voltage range of 3.75V to 20V. The output voltage is set by the ratio of two external resistors as shown in Figure 1. The device servos the output voltage to maintain the voltage at the adjust pin at 3.75V. The current in R1 is then equal to 3.75V/R1. The current in R2 is equal to the sum of the current in R1 and the adjust pin bias current. The adjust pin bias current, 150nA at 25°C, flows through R2 into the adjust pin. The output voltage can be calculated according to the formula in Figure 1. The value of R1 should be less than 400k to minimize errors in the output voltage caused by the adjust pin bias current. Note that in shutdown the output is turned off and the divider current will be zero. Curves of Adjust Pin Voltage vs Temperature and Adjust Pin Bias Current vs Temperature appear in the Typical Performance Characteristics. The reference voltage at the adjust pin has a slight positive temperature coefficient of Power handling capability will be limited by maximum rated junction temperature (125°C). Power dissipated by the device will be made up of two components: IN VOUT OUT LT1121 R2 SHDN + ADJ R1 GND 1121 • F01 ( ) ( ) VOUT = 3.75V 1 + R2 + IADJ • R2 R1 VADJ = 3.75V IADJ = 150nA AT 25°C OUTPUT RANGE = 3.75V TO 30V Figure 1. Adjustable Operation 8 The adjustable device is specified with the adjust pin tied to the output pin. This sets the output voltage to 3.75V. Specifications for output voltage greater than 3.75V will be proportional to the ratio of the desired output voltage to 3.75V (VOUT/3.75V). For example: load regulation for an output current change of 1mA to 150mA is –12mV typical at VOUT = 3.75V. At VOUT = 12V, load regulation would be: 12V × ( –12mV ) = ( –38mV ) 3.75V 1. Output current multiplied by the input/output voltage differential: IOUT × (VIN – VOUT), and 2. Ground pin current multiplied by the input voltage: IGND × VIN. The ground pin current can be found by examining the Ground Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. The LT1121 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal load conditions the maximum junction temperature rating of 125°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. Heat sinking, for surface mount devices, is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated through holes can also be used to spread the heat generated by power devices. Tables 1 through 5 list thermal resistances for each package. Measured values of thermal resistance for several different board sizes and copper areas are listed for each package. All measurements were LT1121/LT1121-3.3/LT1121-5 U W U UO APPLICATI S I FOR ATIO taken in still air, on 3/32" FR-4 board with 1oz copper. All NC leads were connected to the ground plane. Table 1. N8 Package* COPPER AREA TOPSIDE BACKSIDE THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq mm 2500 sq. mm 2500 sq. mm 80°C/W 1000 sq mm 2500 sq. mm 2500 sq. mm 80°C/W 225 sq mm 2500 sq. mm 2500 sq. mm 85°C/W 1000 sq mm 1000 sq. mm 1000 sq. mm 91°C/W Table 5. TO-92 Package THERMAL RESISTANCE Package alone 220°C/W Package soldered into PC board with plated through holes only 175°C/W Package soldered into PC board with 1/4 sq. inch of copper trace per lead 145°C/W Package soldered into PC board with plated through holes in board, no extra copper trace, and a clip-on type heat sink: Thermalloy type 2224B Aavid type 5754 160°C/W 135°C/W * Device is mounted on topside. Leads are through hole and are soldered to both sides of board. Calculating Junction Temperature Table 2. S8 Package COPPER AREA TOPSIDE* BACKSIDE THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq. mm 2500 sq. mm 2500 sq. mm 120°C/W 1000 sq. mm 2500 sq. mm 2500 sq. mm 120°C/W 225 sq. mm 2500 sq. mm 2500 sq. mm 25°C/W 100 sq. mm 1000 sq. mm 1000 sq. mm 131°C/W * Device is mounted on topside. COPPER AREA BACKSIDE BOARD AREA 2500 sq. mm 60°C/W 1000 sq. mm 2500 sq. mm 2500 sq. mm 60°C/W 225 sq. mm 2500 sq. mm 2500 sq. mm 68°C/W 100 sq. mm 2500 sq. mm 2500 sq. mm 74°C/W * Pins 3, 6, and 7 are ground. ** Device is mounted on topside. 2500 sq. mm 2500 sq. mm THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq. mm 50°C/W 1000 sq. mm 2500 sq. mm 2500 sq. mm 50°C/W 225 sq. mm 2500 sq. mm 2500 sq. mm 58°C/W 100 sq. mm 2500 sq. mm 2500 sq. mm 64°C/W 1000 sq. mm 1000 sq. mm 1000 sq. mm 57°C/W 1000 sq. mm 1000 sq. mm 60°C/W BACKSIDE 0 * Tab of device attached to topside copper P = 100mA × (7V – 3.3V) + (5mA × 7V) = 0.405W If we use an SOT-223 package, then the thermal resistance will be in the range of 50°C/W to 65°C/W depending on copper area. So the junction temperature rise above ambient will be less than or equal to: 0.405W × 60°C/W = 24°C Table 4. SOT-223 Package (Thermal Resistance Junction-to-Tab 20°C/W) COPPER AREA IOUT MAX × (VIN MAX – VOUT) + (IGND × VIN) so, 2500 sq. mm 2500 sq. mm TOPSIDE* Power dissipated by the device will be equal to: where, IOUT MAX = 100mA VIN MAX = 7V IGND at (IOUT = 100mA, VIN = 7V) = 5mA Table 3. AS8 Package* TOPSIDE** Example: given an output voltage of 3.3V, an input voltage range of 4.5V to 7V, an output current range of 0mA to 100mA, and a maximum ambient temperature of 50°C, what will the maximum junction temperature be? The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50°C + 24°C = 74°C Output Capacitance and Transient Performance The LTC1121 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 1µF with an ESR of 3Ω or less. For applications where space is very limited, capacitors as low as 0.33µF can be used if combined with a small series resistor. Assuming 9 LT1121/LT1121-3.3/LT1121-5 W U U UO S I FOR ATIO that the ESR of the capacitor is low (ceramic) the suggested series resistor is shown in Table 5. The LT1121 is a micropower device and output transient response will be a function of output capacitance. See the Transient Response curves in the Typical Performance Characteristics. Larger values of output capacitance will decrease the peak deviations and provide improved output transient response. Bypass capacitors, used to decouple individual components powered by the LT1121, will increase the effective value of the output capacitor. Table 5. OUTPUT CAPACITANCE SUGGESTED SERIES RESISTOR 0.33µF 0.47µF 2Ω 1Ω 0.68µF 1Ω >1µF None Needed Protection Features The LT1121 incorporates several protection features which make it 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 device is 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 125°C. The input of the device will withstand reverse voltages of 30V. Current flow into the device will be limited to less than 1mA (typically less than 100µA) and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries that can be plugged in backwards. For fixed voltage versions of the device, the output can be pulled below ground without damaging the device. If the input is open circuit or grounded the output can be pulled below ground by 20V. 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 10 short-circuit current of the device and will protect itself by thermal limiting. For the adjustable version of the device, the output pin is internally clamped at one diode drop below ground. Reverse current for the adjustable device must be limited to 5mA. 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 vary depending on the conditions. Many battery-powered circuits incorporate some form of power management. The following information will help optimize battery life. Table 6 summarizes the following information. The reverse output current will follow the curve in Figure 2 when the input pin is pulled to ground. This current flows through the output pin to ground. The state of the shutdown pin will have no effect on output current when the input pin is pulled to ground. In some applications it may be necessary to leave the input to the LT1121 unconnected when the output is held high. This can happen when the LT1121 is powered from a rectified AC source. If the AC source is removed, then the input of the LT1121 is effectively left floating. The reverse output current also follows the curve in Figure 2 if the input pin is left open. The state of the shutdown pin will have no effect on the reverse output current when the input pin is floating. 100 OUTPUT PIN CURRENT (µA) APPLICATI TJ = 25°C 90 VIN < VOUT CURRENT FLOWS 80 INTO OUTPUT PIN 70 TO GROUND LT1121 (VOUT = VADJ) 60 50 40 LT1121-3.3 30 20 LT1121-5 10 0 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 1121• F02 Figure 2. Reverse Output Current LT1121/LT1121-3.3/LT1121-5 W U U UO APPLICATI S I FOR ATIO 5 VOUT = 3.3V (LT1121-3.3) VOUT = 5V (LT1121-5) 4 INPUT CURRENT (µA) When the input of the LT1121 is forced to a voltage below its nominal output voltage and its output is held high, the reverse output current will still follow the curve in Figure 2. This condition can occur if the input of the LT1121 is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or by a second regulator circuit. When the input pin is forced below the output pin or the output pin is pulled above the input pin, the input current will typically drop to less than 2µA (see Figure 3). The state of the shutdown pin will have no effect on the reverse output current when the output is pulled above the input. 3 2 1 0 0 1 3 2 INPUT VOLTAGE (V) 4 5 1121 F03 Figure 3. Input Current Table 6. Fault Conditions INPUT PIN SHDN PIN OUTPUT PIN < VOUT (Nominal) Open (Hi) Forced to VOUT (Nominal) Reverse Output Current ≈ 15µA (See Figure 2) Input Current ≈ 1µA (See Figure 3) < VOUT (Nominal) Grounded Forced to VOUT (Nominal) Reverse Output Current ≈ 15µA (See Figure 2) Input Current ≈ 1µA (See Figure 3) Open Open (Hi) Forced to VOUT (Nominal) Reverse Output Current ≈ 15µA (See Figure 2) Reverse Output Current ≈ 15µA (See Figure 2) Open Grounded Forced to VOUT (Nominal) ≤ 0.8V Open (Hi) ≤ 0V Output Current = 0 ≤ 0.8V Grounded ≤ 0V Output Current = 0 > 1.5V Open (Hi) ≤ 0V Output Current = Short-Circuit Current – 30V < VIN < 30V Grounded ≤ 0V Output Current = 0 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. 11 LT1121/LT1121-3.3/LT1121-5 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. N8 Package, 8-Lead Plastic DIP 0.300 – 0.320 (7.620 – 8.128) 0.400 (10.160) MAX 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 8 0.009 – 0.015 (0.229 – 0.381) ( +0.025 0.325 –0.015 +0.635 8.255 –0.381 7 0.125 (3.175) MIN 5 0.045 ± 0.015 (1.143 ± 0.381) ) 0.250 ± 0.010 (6.350 ± 0.254) 0.020 (0.508) MIN 1 2 0.010 – 0.020 × 45° (0.254 – 0.508) 4 3 0.018 ± 0.003 (0.457 ± 0.076) 0.100 ± 0.010 (2.540 ± 0.254) S8 Package, 8-Lead Plastic SOIC 0.189 – 0.197 (4.801 – 5.004) 8 0.053 – 0.069 (1.346 – 1.752) 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.008 – 0.010 (0.203 – 0.254) 0.016 – 0.050 0.406 – 1.270 0°– 8° TYP 6 0.065 (1.651) TYP 0.228 – 0.244 (5.791 – 6.197) 0.050 (1.270) BSC 0.014 – 0.019 (0.355 – 0.483) 1 ST Package, 3-Lead Plastic SOT-223 0.248 – 0.264 (6.30 – 6.71) 0.150 – 0.157 (3.810 – 3.988) 2 3 4 0.116 – 0.124 (2.95 – 3.15) 10° – 16° 0.264 – 0.287 (6.71 – 7.29) 0.071 (1.80) MAX 0.130 – 0.146 (3.30 – 3.71) 0.010 – 0.014 (0.25 – 0.36) 10° MAX 10° – 16° 0.025 – 0.033 (0.64 – 0.84) 0.0008 – 0.0040 (0.0203 – 0.1016) 0.012 (0.31) MIN 0.181 (4.60) NOM 0.033 – 0.041 (0.84 – 1.04) 0.090 (2.29) NOM Z Package, 3-Lead Plastic TO-92 0.060 ± 0.005 (1.524± 0.127) DIA 0.060 ± 0.010 (1.524 ± 0.254) 0.180 ± 0.005 (4.572 ± 0.127) 0.180 ± 0.005 (4.572 ± 0.127) 0.140 ± 0.010 (3.556 ± 0.127) 5° NOM 10° NOM 0.90 0.050 (2.286) (1.270) NOM MAX 0.500 (12.79) MIN UNCONTROLLED LEAD DIA 0.020 ± 0.003 (0.508 ± 0.076) 0.015 ± 0.02 (0.381 ± 0.051) 0.050 ± 0.005 (1.270 ± 0.127) 12 Linear Technology Corporation 0.016 ± 0.03 (0.406 ± 0.076) LT/GP 0594 5K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1994