LT1121/LT1121-3.3/LT1121-5 Micropower Low Dropout Regulators with Shutdown U FEATURES DESCRIPTIO ■ The LT®1121/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 3.75V to 30V 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 Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead SOT-23 and 3-Lead TO-92 Packages U APPLICATIO S ■ ■ ■ Low Current Regulator Regulator for Battery-Powered Systems Post Regulator for Switching Supplies 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. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. U TYPICAL APPLICATIO 5V Battery-Powered Supply with Shutdown Dropout Voltage 0.5 IN OUT 1 LT1121-3.3 5V 5 3.3VOUT 150mA + SHDN GND 3 VSHDN (PIN 5) OUTPUT <0.25 OFF >2.8 ON NC ON 0.4 1μF SOLID TANTALUM 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 1121fe 1 LT1121/LT1121-3.3/LT1121-5 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Voltage LT1121 ............................................................. ±30V LT1121HV ............................................. +36V, – 30V Output Pin Reverse Current ................................. 10mA Adjust Pin Current ............................................... 10mA Shutdown Pin Input Voltage (Note 2) ........ 6.5V, – 0.6V Shutdown Pin Input Current (Note 2) .................. 20mA Output Short-Circuit Duration ......................... Indefinite Operating Junction Temperature Range (Note 3) LT1121C-X ........................................... 0°C to 125°C LT1121I-X ....................................... – 40°C to 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C 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 PDIP S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150°C, θJA ≈ 120°C/ W (N8, S8) TJMAX = 150°C, θJA ≈ 70°C/ W (AS8) * 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. ORDER PART NUMBER LT1121CN8 LT1121CN8-3.3 LT1121CN8-5 LT1121IN8 LT1121IN8-3.3 LT1121IN8-5 LT1121CS8 LT1121CS8-3.3 LT1121CS8-5 LT1121HVCS8 LT1121IS8 LT1121IS8-3.3 LT1121IS8-5 LT1121HVIS8 LT1121ACS8 LT1121ACS8-3.3 LT1121ACS8-5 LT1121AHVCS8 LT1121AIS8 LT1121AIS8-3.3 LT1121AIS8-5 LT1121AHVIS8 BOTTOM VIEW FRONT VIEW TAB IS GND 3 OUTPUT 2 GND 1 VIN IN GND OUT ST PACKAGE 3-LEAD PLASTIC SOT-223 Z PACKAGE 3-LEAD PLASTIC TO-92 TJMAX = 150°C, θJA ≈ 50°C/ W TJMAX = 150°C, θJA ≈ 150°C/ W S8 PART MARKING ORDER PART NUMBER ST PART MARKING ORDER PART NUMBER 121I3 121I5 121HVI 1121A 121A3 121A5 1121 121AHV 11213 121AI 11215 121AI3 1121HV 121AI5 1121I 21AHVI LT1121CST-3.3 LT1121IST-3.3 LT1121CST-5 LT1121IST-5 11213 121IS3 11215 1121I5 LT1121CZ-3.3 LT121IZ-3.3 LT1121CZ-5 LT1121IZ-5 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. 1121fe 2 LT1121/LT1121-3.3/LT1121-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Regulated Output Voltage (Note 4) LT1121-3.3 LT1121-5 LT1121 (Note 5) Line Regulation LT1121-3.3 LT1121-5 LT1121 (Note 5) Load Regulation LT1121-3.3 LT1121-5 LT1121 (Note 5) Dropout Voltage (Note 6) Ground Pin Current (Note 7) TYP MAX UNITS VIN = 3.8V, IOUT = 1mA, TJ = 25°C 4.3V < VIN < 20V, 1mA < IOUT < 150mA ● 3.250 3.200 3.300 3.300 3.350 3.400 V V VIN = 5.5V, IOUT = 1mA, TJ = 25°C 6V < VIN < 20V, 1mA < IOUT < 150mA ● 4.925 4.850 5.000 5.000 5.075 5.150 V V VIN = 4.3V, IOUT = 1mA, TJ = 25°C 4.8V < VIN < 20V, 1mA < IOUT < 150mA ● 3.695 3.640 3.750 3.750 3.805 3.860 V V ΔVIN = 4.8V to 20V, IOUT = 1mA ΔVIN = 5.5V to 20V, IOUT = 1mA ● 1.5 10 mV ● 1.5 10 mV ΔVIN = 4.3V to 20V, IOUT = 1mA ΔILOAD = 1mA to 150mA, TJ = 25°C ΔILOAD = 1mA to 150mA ● 1.5 10 mV ● – 12 – 20 – 25 – 40 mV mV ΔILOAD = 1mA to 150mA, TJ = 25°C ΔILOAD = 1mA to 150mA ● – 17 – 28 – 35 – 50 mV mV ΔILOAD = 1mA to 150mA, TJ = 25°C ΔILOAD = 1mA to 150mA ● – 12 – 18 – 25 – 40 mV mV 0.13 0.16 0.25 V V 0.30 0.35 0.50 V V 0.37 0.45 0.60 V V 0.42 0.55 0.70 V V 30 50 μA ILOAD = 1mA, TJ = 25°C ILOAD = 1mA ● ILOAD = 50mA, TJ = 25°C ILOAD = 50mA ● ILOAD = 100mA, TJ = 25°C ILOAD = 100mA ● ILOAD = 150mA, TJ = 25°C ILOAD = 150mA ● ILOAD = 0mA ● ILOAD = 1mA ● 90 120 μA ILOAD = 10mA ● 350 500 μA ILOAD = 50mA ● 1.5 2.5 mA ILOAD = 100mA ● 4.0 7.0 mA ILOAD = 150mA ● 7.0 14.0 mA 150 300 nA 1.2 0.75 2.8 V V 6 10 μA 16 22 Adjust Pin Bias Current (Notes 5, 8) TJ = 25°C Shutdown Threshold VOUT = Off to On VOUT = On to Off ● ● VSHDN = 0V ● Quiescent Current in Shutdown (Note 10) VIN = 6V, VSHDN = 0V ● Ripple Rejection VIN – VOUT = 1V (Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 0.1A Current Limit VIN – VOUT = 7V, TJ = 25°C Input Reverse Leakage Current VIN = –20V, VOUT = 0V Reverse Output Current (Note 11) LT1121-3.3 LT1121-5 LT1121 (Note 5) Shutdown Pin Current (Note 9) MIN 50 58 200 ● VOUT = 3.3V, VIN = 0V VOUT = 5V, VIN = 0V VOUT = 3.8V, VIN = 0V Note 1: 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. 0.25 16 16 16 μA dB 500 mA 1.0 mA 25 25 25 μA μA μA Note 2: 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 1121fe 3 LT1121/LT1121-3.3/LT1121-5 ELECTRICAL CHARACTERISTICS 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 3: 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 4: 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 5: The LT1121 (adjustable version) is tested and specified with the adjust pin connected to the output pin. Note 6: 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 7: 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 8: Adjust pin bias current flows into the adjust pin. Note 9: Shutdown pin current at VSHDN = 0V flows out of the shutdown pin. Note 10: Quiescent current in shutdown is equal to the sum total of the shutdown pin current (6μA) and the ground pin current (9μA). Note 11: 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. U W TYPICAL PERFOR A CE CHARACTERISTICS 0.6 TJ ≤ 125°C 0.5 TJ ≤ 25°C 0.3 0.2 0.1 50 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) –25 100 1121 G27 120 TJ = 25°C RLOAD = ∞ VSHDN = OPEN 60 40 20 80 VSHDN = OPEN 60 40 20 VSHDN = 0V 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 1121 G04 80 VSHDN = OPEN 60 40 20 VSHDN = 0V 0 0 TJ = 25°C RLOAD = ∞ VOUT = VADJ 100 QUIESCENT CURRENT (μA) 100 QUIESCENT CURRENT (μA) 100 125 LT1121 Quiescent Current 120 TJ = 25°C RLOAD = ∞ 80 100 1121 G11 LT1121-5 Quiescent Current 120 50 25 0 75 TEMPERATURE (°C) 1121 G14 LT1121-3.3 Quiescent Current QUIESCENT CURRENT (μA) 0 –50 –25 125 VSHDN = 0V 0 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 1121 G02 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 1121 G03 1121fe 4 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS LT1121-3.3 Output Voltage LT1121-5 Output Voltage 3.83 5.08 3.38 IOUT = 1mA IOUT = 1mA 5.06 3.81 3.34 5.04 3.79 3.32 3.30 3.28 3.26 3.24 50 25 0 75 TEMPERATURE (°C) –25 100 5.02 5.00 4.98 3.69 50 25 0 75 TEMPERATURE (°C) –25 100 800 500 RLOAD = 330Ω ILOAD = 10mA* 300 *FOR VOUT = 3.3V 200 RLOAD = 3.3k ILOAD = 1mA* 100 800 600 500 RLOAD = 500Ω ILOAD = 10mA* 400 300 *FOR VOUT = 5V 200 RLOAD = 5k ILOAD = 1mA* 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 1121 G10 10 TJ = 25°C RLOAD = 33Ω ILOAD = 100mA* 4 3 RLOAD = 66Ω ILOAD = 50mA* 2 1 1 2 300 *FOR VOUT = 3.75V 200 3 4 5 6 7 INPUT VOLTAGE (V) 9 10 1121 G09 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 1121 G08 TJ = 25°C 9 VOUT = VADJ 6 RLOAD = 50Ω ILOAD = 100mA* 5 4 3 RLOAD = 100Ω ILOAD = 50mA* 2 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 RLOAD = 25Ω ILOAD = 150mA* 7 6 5 RLOAD = 38Ω ILOAD = 100mA* 4 3 RLOAD = 75Ω ILOAD = 50mA* 2 1 *FOR VOUT = 5V 0 10 10 RLOAD = 33Ω ILOAD = 150mA* 7 9 LT1121 Ground Pin Current 8 0 8 RLOAD = 3.8k ILOAD = 1mA* 0 10 TJ = 25°C 1 *FOR VOUT = 3.3V 0 GROUND PIN CURRENT (mA) GROUND PIN CURRENT (mA) 6 5 9 9 RLOAD = 22Ω ILOAD = 150mA* 7 RLOAD = 380Ω ILOAD = 10mA* 400 LT1121-5 Ground Pin Current 9 8 500 1121 G06 LT1121-3.3 Ground Pin Current 10 600 0 0 10 GROUND PIN CURRENT (mA) 1 RLOAD = 150Ω ILOAD = 25mA* 100 0 0 0 TJ = 25°C 700 VOUT = VADJ RLOAD = 200Ω ILOAD = 25mA* 100 0 125 100 LT1121 Ground Pin Current TJ = 25°C 700 GROUND PIN CURRENT (μA) GROUND PIN CURRENT (μA) 700 RLOAD = 130Ω ILOAD = 25mA* 50 25 0 75 TEMPERATURE (°C) –25 1121 G24 LT1121-5 Ground Pin Current TJ = 25°C 400 3.67 –50 125 1121 G23 LT1121-3.3 Ground Pin Current 600 3.73 4.94 1121 G22 800 3.75 3.71 4.92 –50 125 IOUT = 1mA 3.77 4.96 GROUND PIN CURRENT (μA) 3.22 –50 ADJ PIN VOLTAGE (V) 3.36 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) LT1121 Adjust Pin Voltage 8 9 10 1121 G05 0 *FOR VOUT = 3.75V 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 1121 G07 1121fe 5 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Shutdown Pin Threshold (On-to-Off) Ground Pin Current 2.0 VIN = 3.3V (LT1121-3.3) VIN = 5V (LT1121-5) 12 V = 3.75V (LT1121) IN DEVICE IS OPERATING 10 IN DROPOUT TJ = 25°C 6 TJ = –55°C 4 2 1.8 1.6 SHUTDOWN THRESHOLD (V) TJ = 125°C 8 2.0 ILOAD = 1mA 1.8 SHUTDOWN THRESHOLD (V) GROUND PIN CURRENT (mA) 14 Shutdown Pin Threshold (Off-to-On) 1.4 1.2 1.0 0.8 0.6 0.4 0 20 0 –50 40 60 80 100 120 140 160 OUTPUT CURRENT (mA) 50 25 0 75 TEMPERATURE (°C) –25 100 1121 G29 6 5 4 3 2 1 –25 50 25 0 75 TEMPERATURE (°C) 100 20 15 10 5 0 1 7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V) 10 5 250 200 150 100 50 125 1121 G13 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G25 Current Limit VOUT = 0V 350 VIN = 7V 350 VOUT = 0V 300 300 250 200 150 100 250 200 150 100 50 0 100 –25 400 50 50 25 0 75 TEMPERATURE (°C) 125 300 0 –50 9 CURRENT LIMIT (mA) SHORT-CIRCUIT CURRENT (mA) OUTPUT PIN CURRENT (μA) 15 100 350 Current Limit 400 20 50 25 0 75 TEMPERATURE (°C) 1121 G28 Reverse Output Current VIN = 0V VOUT = 5V (LT1121-5) 25 VOUT = 3.3V (LT1121-3.3) VOUT = 3.8V (LT1121) –25 400 0 125 30 –25 0.4 LT1121 Adjust Pin Bias Current 1121 G15 0 –50 0.6 1121 G17 ADJUST PIN BIAS CURRENT (nA) 7 0 –50 0.8 0 –50 125 25 VSHDN = 0V 8 ILOAD = 1mA 1.0 Shutdown Pin Input Current SHUTDOWN PIN INPUT CURRENT (mA) SHUTDOWN PIN CURRENT (μA) 9 1.2 1121 G16 Shutdown Pin Current 10 ILOAD = 150mA 1.4 0.2 0.2 0 1.6 0 1 4 3 2 5 INPUT VOLTAGE (V) 6 7 1121 G20 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G19 1121fe 6 LT1121/LT1121-3.3/LT1121-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Ripple Rejection 64 62 RIPPLE REJECTION (dB) LT1121 (VOUT = VADJ) 60 50 40 LT1121-3.3 30 80 60 58 56 54 0 52 LT1121-5 60 50 40 30 COUT = 1μF SOLID TANTALUM 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 50 –50 10 0 –25 50 25 0 75 TEMPERATURE (°C) ΔILOAD = 1mA TO 150mA OUTPUT VOLTAGE DEVIATION (V) –5 LT1121* 125 10 LT1121-3.3 –15 –20 100 1k 10k FREQUENCY (Hz) 100k 1M 1121 G26 LT1121-5 Load Transient Response Load Regulation –10 100 1121 G18 1121 G01 0 COUT = 47μF SOLID TANTALUM 70 20 20 10 LT1121-5 Load Transient Response VIN = 6V 0.2 CIN = 0.1μF = 1μF C 0.1 OUT 0 –0.1 –0.2 VIN = 6V 0.2 CIN = 0.1μF COUT = 3.3μF 0.1 0 –0.1 –0.2 LT1121-5 –30 –35 * ADJ PIN TIED TO OUTPUT PIN –40 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1121 G21 LOAD CURRENT (mA) –25 LOAD CURRENT (mA) LOAD REGULATION (mV) IOUT = 100mA 90 VIN = 6V + 50mVRMS RIPPLE VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz IOUT = 100mA OUTPUT VOLTAGE DEVIATION (V) OUTPUT PIN CURRENT (μA) TJ = 25°C 90 VIN = 0V CURRENT FLOWS 80 INTO OUTPUT PIN 70 Ripple Rejection 100 RIPPLE REJECTION (dB) Reverse Output Current 100 150 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms) 1121 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 1121fe 7 LT1121/LT1121-3.3/LT1121-5 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 six 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. 1121fe 8 LT1121/LT1121-3.3/LT1121-5 U W U U APPLICATIO 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. Adjustable Operation 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 ⎠ ( ) ( ) Thermal Considerations The adjustable version of the LT1121 has an output voltage range of 3.75V to 30V. 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 IN VOUT OUT LT1121 R2 SHDN ADJ + R1 GND 1121 • F01 ( approximately 15ppm/°C. The adjust pin bias current has a negative temperature coefficient. These effects are small and will tend to cancel each other. ) ( ) 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 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: 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 1121fe 9 LT1121/LT1121-3.3/LT1121-5 U W U U APPLICATIO 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 125°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 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 60°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 LT1121 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 1121fe 10 LT1121/LT1121-3.3/LT1121-5 U W U U APPLICATIO S I FOR ATIO Table 6. Suggested Series Resistor Values SUGGESTED SERIES OUTPUT CAPACITANCE RESISTOR 0.33μF 2Ω 0.47μF 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 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 7 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) that the ESR of the capacitor is low (ceramic) the suggested series resistor is shown in Table 6. 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. 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 1121fe 11 LT1121/LT1121-3.3/LT1121-5 U W U U APPLICATIO 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 7. 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 1121fe 12 LT1121/LT1121-3.3/LT1121-5 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .300 – .325 (7.620 – 8.255) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 8.255 +0.889 –0.381 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) ) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC (0.457 ± 0.076) N8 1002 NOTE: 1. DIMENSIONS ARE INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.483) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 2 3 4 .004 – .010 (0.101 – 0.254) .050 (1.270) BSC SO8 0303 1121fe 13 LT1121/LT1121-3.3/LT1121-5 U PACKAGE DESCRIPTIO ST Package 3-Lead Plastic SOT-223 (LTC DWG # 05-08-1630) .248 – .264 (6.30 – 6.71) .129 MAX .114 – .124 (2.90 – 3.15) .059 MAX .264 – .287 (6.70 – 7.30) .248 BSC .130 – .146 (3.30 – 3.71) .039 MAX .059 MAX .181 MAX .033 – .041 (0.84 – 1.04) .0905 (2.30) BSC .090 BSC RECOMMENDED SOLDER PAD LAYOUT 10° – 16° .010 – .014 (0.25 – 0.36) 10° MAX .071 (1.80) MAX 10° – 16° .024 – .033 (0.60 – 0.84) .181 (4.60) BSC .012 (0.31) MIN .0008 – .0040 (0.0203 – 0.1016) ST3 (SOT-233) 0502 1121fe 14 LT1121/LT1121-3.3/LT1121-5 U PACKAGE DESCRIPTIO Z Package 3-Lead Plastic TO-92 (Similar to TO-226) (LTC DWG # 05-08-1410) .180 ± .005 (4.572 ± 0.127) .060 ± .005 (1.524± 0.127) DIA .90 (2.286) NOM .180 ± .005 (4.572 ± 0.127) .500 (12.70) MIN .050 UNCONTROLLED (1.270) LEAD DIMENSION MAX .016 ± .003 (0.406 ± 0.076) .050 (1.27) BSC 5° NOM .015 ± .002 (0.381 ± 0.051) Z3 (TO-92) 0801 .060 ± .010 (1.524 ± 0.254) 3 2 .098 +.016/–.04 (2.5 +0.4/–0.1) 2 PLCS TO-92 TAPE AND REEL REFER TO TAPE AND REEL SECTION OF LTC DATA BOOK FOR ADDITIONAL INFORMATION .140 ± .010 (3.556 ± 0.127) 1 10° NOM 1121fe 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. 15 LT1121/LT1121-3.3/LT1121-5 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1120 125mA Low Dropout Regulator with 20μA IQ Includes 2.5V Reference and Comparator LT1129 700mA Micropower Low Dropout Regulator 50μA Quiescent Current LT1175 500mA Negative Low Dropout Micropower Regulator 45μA IQ, 0.26V Dropout Voltage, SOT-223 Package LT1521 300mA Low Dropout Micropower Regulator with Shutdown 15μA IQ, Reverse Battery Protection LT1529 3A Low Dropout Regulator with 50μA IQ 500mV Dropout Voltage LT1611 Inverting 1.4MHz Switching Regulator 5V to – 5V at 150mA, Low Output Noise, SOT-23 Package LT1613 1.4MHz Single-Cell Micropower DC/DC Converter SOT-23 Package, Internally Compensated LTC1627 High Efficiency Synchronous Step-Down Switching Regulator Burst ModeTM Operation, Monolithic, 100% Duty Cycle LT1682 Doubler Charge Pump with Low Noise Linear Regulator Low Output Noise: 60μVRMS (100kHz BW) LT1762 Series 150mA, Low Noise, LDO Micropower Regulator 25μA Quiescent Current, 20μVRMS Noise LT1763 Series 500mA, Low Noise, LDO Micropower Regulator 30μA Quiescent Current, 20μVRMS Noise LT1764 Series 3A Fast Transient Response LDO 300mV Dropout, 40μVRMS Noise LT1962 Series 300mA, Low Noise, LDO Micropower Regulator 30μA Quiescent Current, 20μVRMS Noise LT1963 Series 1.5A Fast Transient Response LDO 300mV Dropout, 40μVRMS Noise Burst Mode is a trademark of Linear Technology Corporation. 1121fe 16 Linear Technology Corporation LT 0407 REV E • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com © LINEAR TECHNOLOGY CORPORATION 1994