LT1521/LT1521-3 LT1521-3.3/LT1521-5 300mA Low Dropout Regulators with Micropower Quiescent Current and Shutdown U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT ®1521/LT1521-3/LT1521-3.3/LT1521-5 are low dropout regulators with micropower quiescent current and shutdown. These devices are capable of supplying 300mA of output current with a dropout voltage of 0.5V. Designed for use in battery-powered systems, the low quiescent current, 12µA operating and 6µA 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. Dropout Voltage: 0.5V Output Current: 300mA Quiescent Current: 12µA No Protection Diodes Needed Adjustable Output from 3.8V to 20V Fixed Output Voltages: 3V, 3.3V, 5V Controlled Quiescent Current in Dropout Shutdown IQ = 6µA Reverse Battery Protection No Reverse Current Thermal Limiting Other features of the LT1521/LT1521-3/LT1521-3.3/ LT1521-5 include the ability to operate with very small output capacitors. They are stable with only 1.5µF on the output while most older devices require between 10µF and 100µF for stability. Small ceramic capacitors can be used, enhancing manufacturability. Also, the input may be connected to voltages lower than the output voltage, including negative voltages, without reverse current flow from output to input. This makes the LT1521 series ideal for backup power situations where the output is held high and the input is low or reversed. Under these conditions only 5µA will flow from the output pin to ground. U APPLICATIONS ■ ■ ■ Low Current Regulator Regulator for Battery-Powered Systems Post Regulator for Switching Supplies , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION Dropout Voltage 5V Battery-Powered Supply with Shutdown 8 IN OUT 0.6 5V 300mA 1 + 1µF 5 SHDN SENSE 0.5 1.5µF LT1521-5 2 GND 3 VSHDN (PIN 5) OUTPUT <0.25 OFF >2.80 ON NC ON DROPOUT VOLTAGE (V) 6V 0.4 0.3 0.2 0.1 LT1521 • TA01 0 0 50 100 150 200 250 OUTPUT CURRENT (mA) 300 LT1521 • TA02 1 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage ...................................................... ± 20V* 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) ..................... 5mA Output Short-Circuit Duration .......................... Indefinite Storage Temperature Range ................. – 65°C to 150°C Operating Junction Temperature Range (Note 2) Commercial ........................................... 0°C to 125°C Industrial ......................................... – 40°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C *For applications requiring input voltage ratings greater than 20V, contact the factory. U W U PACKAGE/ORDER INFORMATION TOP VIEW TOP VIEW OUT SENSE/ADJ* NC GND 8 7 6 5 1 2 3 4 IN NC NC SHDN MS8 PACKAGE 8-LEAD PLASTIC MSOP *PIN 2 = SENSE FOR LT1521-3/ LT1521-3.3/LT1521-5 PIN 2 = ADJ FOR LT1521 8 IN SENSE/ADJ* 2 7 GND GND 3 6 GND NC 4 5 SHDN S8 PACKAGE 8-LEAD PLASTIC SO TAB IS GND 1 OUT 2 GND 3 IN ST PACKAGE 3-LEAD PLASTIC SOT-223 *PIN 2 = SENSE FOR LT1521-3/LT1521-3.3/LT1521-5 = ADJ FOR LT1521 TJMAX = 125°C, θJA = 70°C/ W SEE THE APPLICATIONS INFORMATION SECTION TJMAX = 125 °C, θJA = 50°C/ W SEE THE APPLICATIONS INFORMATION SECTION ORDER PART NUMBER ORDER PART NUMBER ORDER PART NUMBER LT1521CMS8 LT1521CMS8-3 LT1521CMS8-3.3 LT1521CMS8-5 LT1521CS8 LT1521CS8-3 LT1521CS8-3.3 LT1521CS8-5 LT1521IS8 LT1521IS8-3 LT1521IS8-3.3 LT1521IS8-5 LT1521CST-3 LT1521CST-3.3 LT1521CST-5 LT1521IST-3 LT1521IST-3.3 LT1521IST-5 TJMAX = 125°C, θJA = 125°C/ W MS8 PART MARKING LTEZ LTFB LTDU LTFA Consult factory for Military grade parts. 2 FRONT VIEW OUT 1 S8 PART MARKING 1521 15213 152133 15215 1521I 1521I3 1521I33 1521I5 ST PART MARKING 15213 152133 15215 1521I3 1521I33 1521I5 LT1521/LT1521-3 LT1521-3.3/LT1521-5 ELECTRICAL CHARACTERISTICS PARAMETER Regulated Output Voltage (Note 4) Line Regulation Load Regulation Dropout Voltage (Note 6) Ground Pin Current (Note 7) Adjust Pin Bias Current (Notes 5, 8) Shutdown Threshold Shutdown Pin Current (Note 9) Quiescent Current in Shutdown (Note 10) Ripple Rejection Current Limit CONDITIONS LT1521-3 VIN = 3.5V, IOUT = 1mA, TJ = 25°C 4V < VIN < 20V, 1mA < IOUT < 300mA LT1521-3.3 VIN = 3.8V, IOUT = 1mA, TJ = 25°C 4.3V < VIN < 20V, 1mA < IOUT < 300mA LT1521-5 VIN = 5.5V, IOUT = 1mA, TJ = 25°C 6V < VIN < 20V, 1mA < IOUT < 300mA LT1521 (Note 5) VIN = 4.3V, IOUT = 1mA, TJ = 25°C 4.8V < VIN < 20V, 1mA < IOUT < 300mA LT1521-3 ∆VIN = 4.5 to 20V, IOUT = 1mA LT1521-3.3 ∆VIN = 4.8 to 20V, IOUT = 1mA LT1521-5 ∆VIN = 5.5 to 20V, IOUT = 1mA LT1521 (Note 5) ∆VIN = 4.3 to 20V, IOUT = 1mA LT1521-3 ∆ILOAD = 1mA to 300mA, TJ ≤ 25°C LT1521-3.3 ∆ILOAD = 1mA to 300mA, TJ ≤ 25°C LT1521-5 ∆ILOAD = 1mA to 300mA, TJ ≤ 25°C LT1521 (Note 5) ∆ILOAD = 1mA to 300mA, TJ ≤ 25°C LT1521-3 ∆ILOAD = 1mA to 300mA, TJ >25°C LT1521-3.3 ∆ILOAD = 1mA to 300mA, TJ > 25°C LT1521-5 ∆ILOAD = 1mA to 300mA, TJ > 25°C LT1521 (Note 5) ∆ILOAD = 1mA to 300mA, TJ > 25°C 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 = 300mA, TJ = 25°C ILOAD = 300mA ILOAD = 0mA ILOAD = 1mA ILOAD = 10mA ILOAD = 50mA ILOAD = 100mA ILOAD = 150mA ILOAD = 300mA TJ = 25°C VOUT = Off to On VOUT = On to Off VSHDN = 0V VIN = VOUT (NOMINAL) + 1V, VSHDN = 0V VIN – VOUT = 1V(Avg), VRIPPLE = 0.5VP–P, fRIPPLE = 120Hz, ILOAD = 150mA VIN – VOUT = 7V, TJ = 25°C VIN = VOUT (NOMINAL) + 1.5V, ∆VOUT = – 0.1V ● ● ● ● MIN 2.950 2.900 3.250 3.200 4.925 4.850 3.695 3.640 ● ● ● ● TYP 3.000 3.000 3.300 3.300 5.000 5.000 3.750 3.750 1.5 1.5 1.5 1.5 – 20 – 20 – 25 – 20 – 20 – 20 – 25 – 20 130 ● 290 ● 350 ● 400 ● 500 ● 50 12 65 300 0.8 1.4 2.2 6.5 50 1.20 0.75 2.0 6 58 320 400 400 ● ● ● ● ● ● ● ● ● 0.25 ● ● ● MAX 3.050 3.100 3.350 3.400 5.075 5.150 3.805 3.860 20 20 20 20 – 30 – 30 – 45 – 30 – 55 – 55 – 75 – 55 170 250 350 450 420 550 470 600 600 750 20 100 450 1.5 2.5 4.0 12.0 100 2.80 5.0 12 800 UNITS V V V V V V V V mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV µA µA µA mA mA mA mA nA V V µA µA dB mA mA 3 LT1521/LT1521-3 LT1521-3.3/LT1521-5 ELECTRICAL CHARACTERISTICS PARAMETER Input Reverse Leakage Current Reverse Output Current (Note 11) CONDITIONS VIN = – 20V, VOUT = 0V LT1521-3 VOUT = 3V, VIN < 3V, TJ = 25°C LT1521-3.3 VOUT = 3.3V, VIN < 3.3V, TJ = 25°C LT1521-5 VOUT = 5V, VIN < 5V, TJ = 25°C LT1521 (Note 5) VOUT = 3.8V, VIN < 3.75V, TJ = 25°C The ● denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 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 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 5mA. 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. MIN TYP ● 5 5 5 5 MAX 1.0 10 10 10 10 UNITS mA µA µA µA µA Note 5: The LT1521 (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 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 total sum of the shutdown pin current (2µA) and the ground pin current (4µA). 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 PERFORMANCE CHARACTERISTICS Guaranteed Dropout Voltage Dropout Voltage Quiescent Current 0.8 0.8 15.0 = TEST POINTS 0.7 0.6 0.5 TJ ≤ 25°C 0.4 0.3 0.2 0.1 0 0 50 100 200 250 150 OUTPUT CURRENT (mA) 300 LT1521 • TPC01 4 0.5 ILOAD = 150mA ILOAD = 100mA 0.4 0.3 0.2 ILOAD = 50mA 0.1 ILOAD = 1mA 0 –50 –25 VSHDN = OPEN 12.5 ILOAD = 300mA 0.6 0 50 75 25 TEMPERATURE (°C) QUIESCENT CURRENT (µA) TJ ≤ 125°C DROPOUT VOLTAGE (V) DROPOUT VOLTAGE (V) 0.7 10.0 7.5 2.5 100 125 LT1521 • TPC02 VSHDN = 0V 5.0 VIN = 6V RL = ∞ ILOAD = 0 0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 LT1521 • TPC03 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W TYPICAL PERFORMANCE CHARACTERISTICS LT1521-3 Output Voltage LT1521-3.3 Output Voltage 3.38 3.36 3.04 3.34 OUTPUT VOLTAGE (V) 3.06 3.02 3.00 2.98 2.96 5.08 IOUT = 1mA 5.06 OUTPUT VOLTAGE (V) 3.08 3.32 3.30 3.28 3.26 3.24 2.94 2.92 –50 –25 0 50 75 25 TEMPERATURE (°C) 100 3.22 –50 125 75 50 25 TEMPERATURE (°C) –25 3.75 3.73 3.71 30 25 20 15 0 100 VSHDN = OPEN 10 3.67 –50 125 VSHDN = 0V 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 25 20 15 10 8 9 0 10 QUIESCENT CURRENT (µA) 35 30 25 20 VSHDN = OPEN 10 VSHDN = 0V 8 9 10 LT1521 • TPC10 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 1000 40 35 30 25 20 15 TJ = 25°C *FOR VOUT = 3V 900 VSHDN = OPEN 10 VSHDN = 0V 800 RLOAD = 60Ω ILOAD = 50mA* 700 600 RLOAD = 120Ω ILOAD = 25mA* 500 400 RLOAD = 300Ω ILOAD = 10mA* 300 200 RLOAD = 3k ILOAD = 1mA* 100 0 3 4 5 6 7 INPUT VOLTAGE (V) 1 LT1521 • TPC09 TJ = 25°C RL = ∞ 5 0 0 LT1521-3 Ground Pin Current 45 40 2 30 5 50 TJ = 25°C RL = ∞ 45 125 35 LT1521 Quiescent Current 50 1 40 LT1521 • TPC08 LT1521 • TPC07 LT1521-5 Quiescent Current 100 TJ = 25°C RL = ∞ 45 35 5 50 75 25 TEMPERATURE (°C) 50 75 25 TEMPERATURE (°C) 50 TJ = 25°C RL = ∞ 40 3.69 0 0 LT1521 • TPC06 QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) OUTPUT VOLTAGE (V) 3.77 0 4.96 LT1521-3.3 Quiescent Current 45 3.79 5 4.98 4.92 –50 –25 125 50 ILOAD = 1mA 15 5.00 LT1521-3 Quiescent Current 3.83 –25 5.02 LT1521 • TPC05 LT1521 Adjust Pin Voltage QUIESCENT CURRENT (µA) 100 0 LT1521 • TPC04 3.81 5.04 4.94 GROUND PIN CURRENT (µA) OUTPUT VOLTAGE (V) LT1521-5 Output Voltage 0 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 LT1521 • TPC11 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 LT1521 • TPC12 5 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W TYPICAL PERFORMANCE CHARACTERISTICS LT1521-3 Ground Pin Current LT1521-3.3 Ground Pin Current 8 8 1000 GROUND PIN CURRENT (µA) 6 RLOAD = 10Ω ILOAD = 300mA* 5 4 RLOAD = 20Ω ILOAD = 150mA* 3 2 RLOAD = 30Ω ILOAD = 100mA* 1 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 800 600 RLOAD = 132Ω ILOAD = 25mA* 500 400 RLOAD = 330Ω ILOAD = 10mA* 300 200 0 10 RLOAD = 3.3k ILOAD = 1mA* 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) RLOAD = 200Ω ILOAD = 25mA* RLOAD = 500Ω ILOAD = 10mA* 300 200 RLOAD = 5k ILOAD = 1mA* 100 5 4 RLOAD = 33.3Ω ILOAD = 150mA* 3 2 1 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) GROUND PIN CURRENT (mA) 4 RLOAD = 25Ω ILOAD =150mA* 3 2 1 RLOAD = 37.5Ω ILOAD =100mA* 0 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 800 10 LT1521 • TPC19 RLOAD = 75Ω ILOAD = 50mA* 700 600 RLOAD = 150Ω ILOAD = 25mA* 500 400 RLOAD = 375Ω ILOAD = 10mA* 300 200 0 8 9 10 RLOAD = 3.8k ILOAD = 1mA* 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 8 9 10 LT1521 • TPC18 Shutdown Pin Threshold (On-to-Off) 8 7 6 5 TJ = 25°C 4 1.8 TJ = 125°C TJ = 55°C 3 2 ILOAD = 1mA 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 1 9 10 9 2.0 VIN = 3V (LT1521-3) VIN = 3.3V (LT1521-3.3) VIN = 5V (LT1521-5) VIN = 3.75V (LT1521) DEVICE IS OPERATING IN DROPOUT 9 5 8 VOUT = VADJ *FOR VOUT = 3.75V 100 10 RLOAD = 12.5Ω ILOAD =300mA* 6 3 4 5 6 7 INPUT VOLTAGE (V) LT1521 • TPC17 8 7 2 TJ = 25°C 900 Ground Pin Current TJ = 25°C VOUT = VADJ *FOR VOUT = 3.75V 1 LT1521 • TPC15 RLOAD = 50Ω ILOAD = 100mA* 0 0 RLOAD = 33Ω ILOAD = 100mA* LT1521 Ground Pin Current 6 LT1521 Ground Pin Current GROUND PIN CURRENT (mA) 10 RLOAD = 16.7Ω ILOAD = 300mA* LT1521 • TPC16 6 9 SHUTDOWN PIN THRESHOLD (V) 400 0 8 GROUND PIN CURRENT (µA) GROUND PIN CURRENT (mA) GROUND PIN CURRENT (µA) 700 500 2 1000 TJ = 25°C *FOR VOUT = 5V 7 RLOAD = 100Ω ILOAD = 50mA* RLOAD = 22Ω ILOAD = 150mA* 3 0 8 600 4 LT1521-5 Ground Pin Current 1000 800 RLOAD = 11Ω ILOAD = 300mA* 5 LT1521 • TPC14 LT1521-5 Ground Pin Current TJ = 25°C *FOR VOUT = 5V 6 1 LT1521 • TPC13 900 TJ = 25°C *FOR VOUT = 3.3V 7 RLOAD = 66Ω ILOAD = 50mA* 700 100 0 0 TJ = 25°C *FOR VOUT = 3.3V 900 GROUND PIN CURRENT (mA) TJ = 25°C *FOR VOUT = 3V 7 GROUND PIN CURRENT (mA) LT1521-3.3 Ground Pin Current 0 0 50 250 150 200 100 OUTPUT CURRENT (mA) 300 LT1521 • TPC20 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 LT1521 • TPC21 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Pin Threshold (Off-to-On) 3.0 25 SHUTDOWN PIN CURRENT (µA) ILOAD = 300mA 1.6 1.4 1.2 ILOAD = 1mA 1.0 0.8 0.6 0.4 SHUTDOWN PIN INPUT CURRENT (mA) VSHDN = 0V 1.8 SHUTDOWN PIN THRESHOLD (V) Shutdown Pin Input Current Shutdown Pin Current 2.0 2.5 2.0 1.5 1.0 0.5 0.2 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 0 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 45 150 125 100 75 50 25 TJ = 25°C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN VOUT = VSENSE (LT1521-3/LT1521-3.3 LT1521-5) VOUT = VADJ (LT1521) 40 35 30 25 100 15 Current Limit LT1521-5 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 0.2 0.1 0.1 125 LT1521 • TPC28 1 4 3 5 2 INPUT VOLTAGE (V) 6 5 6 7 Ripple Rejection 66 VIN = 0V VOUT = 3V (LT1521-3) VOUT = 3.3V (LT1521-3.3) VOUT = 5V (LT1521-5) VOUT = 3.75V (LT1521) 64 4 3 2 0 –50 –25 VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz ILOAD = 150mA 62 60 58 56 54 1 100 0 LT1521 • TPC27 RIPPLE REJECITON (dB) 7 0.2 50 25 75 0 TEMPERATURE (°C) 0.3 Reverse Output Current VIN = 7V VOUT = 0V 0 –50 –25 0.4 0 10 8 OUTPUT PIN CURRENT (µA) SHORT-CIRCUIT CURRENT (A) VOUT = 0V LT1521-3 0 9 0.5 LT1521 • TPC26 0.6 0.3 7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V) Current Limit 10 0 125 0.4 1 LT1521 • TPC24 LT1521 LT1521 • TPC25 0.5 0 0.6 LT1521-3.3 20 5 75 50 25 TEMPERATURE (°C) 5 0 125 SHORT-CIRCUIT CURRENT (A) 175 0 10 Reverse Output Current 50 REVERSE OUTPUT CURRENT (µA) ADJUST PIN BIAS CURRENT (nA) Adjust Pin Bias Current 200 –25 15 LT1521 • TPC23 LT1521 • TPC22 0 –50 100 20 75 50 25 TEMPERATURE (°C) 0 100 125 LT1521 • TPC29 52 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 LT1521 • TPC30 7 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation Ripple Rejection 0 100 ILOAD = 150mA VIN = 6V + 50mVRMS RIPPLE 90 –5 LOAD REGULATION (mV) RIPPLE REJECTION (dB) 80 70 60 COUT = 33µF SOLID TANTALUM 50 40 30 20 COUT = 3.3µF SOLID TANTALUM 10 0 10 100 1k 10k FREQUENCY (Hz) 100k ∆ILOAD = 1mA TO 300mA –10 LT1521-5 LT1521-3 –15 LT1521* –25 –30 –35 VIN = VOUT (NOMINAL + 1V) *VADJ = VOUT –40 –50 –25 1M LT1521-3.3 –20 0 50 75 25 TEMPERATURE (°C) LT1521 • TPC31 OUTPUT VOLTAGE DEVIATION (V) OUTPUT VOLTAGE DEVIATION (V) LT1521-5 Transient Response VIN = 6V CIN = 0.1µF COUT = 1.5µF 0.1 0 –0.1 –0.2 0.2 0.1 VIN = 6V CIN = 0.1µF COUT = 33µF 0 –0.1 –0.2 LOAD CURRENT (mA) LOAD CURRENT (mA) 125 LT1521 • TPC32 LT1521-5 Transient Response 0.2 100 150 100 50 0 50 100 150 200 250 300 350 400 450 500 TIME (µs) LT1521 • TPC33 300 200 100 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 TIME (ms) LT1521 • TPC34 U U U PIN FUNCTIONS OUT (Pin 1): The output pin supplies power to the load. A minimum output capacitor of 1.5µF is required to prevent oscillations, but larger values of output capacitor will be necessary to deal with larger load transients. See the Applications Information section for more on output capacitance and reverse output characteristics. SENSE (Pin 2): For fixed voltage versions of the LT1521 (LT1521-3, LT1521-3.3, LT1521-5), 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 8 the output pin of the regulator. In critical applications small voltage drops caused by the resistance (RP) of PC traces between the regulator and the load, which would normally degrade regulation, may be eliminated by connecting the sense pin to the output at the load as shown in Figure 1 (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 5µA at the nominal regulated output voltage. This pin is internally clamped to – 0.6V (one VBE). LT1521/LT1521-3 LT1521-3.3/LT1521-5 U U U PIN FUNCTIONS 5 + VIN IN OUT 1 RP LT1521 4 SHDN SENSE + 2 LOAD GND 3 RP LT1521 • F01 Figure 1. Kelvin Sense Connection ADJ (Pin 2): For adjustable LT1521, 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 50nA which flows into the pin. See Adjust Pin Bias Current vs Temperature in the Typical Performance Characteristics section. 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 20V. SHDN (Pin 5): The shutdown 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 1.7µA. 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 pull-up 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 5mA. A curve of the 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. IN (Pin 8): 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 battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1µF to 10µF is sufficient. The LT1521 is designed to withstand reverse voltages on the input pin with respect to ground and the output pin. In the case of reversed input, which can happen if a battery is plugged in backwards, the LT1521 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1521 and no reverse voltage will appear at the load. The device will protect both itself and the load. U W U U APPLICATIONS INFORMATION The LT1521 is a 300mA low dropout regulator with micropower quiescent current and shutdown. The device is capable of supplying 300mA at a dropout of 0.5V and operates with very low quiescent current (12µA). In shutdown, the quiescent current drops to only 6µA. In addition to the low quiescent current, the LT1521 incorporates several protection features which make it ideal for use in battery-powered 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 LT1521 acts like it has a diode in series with its output and prevents reverse current flow. Adjustable Operation The adjustable version of the LT1521 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 2. 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, 50nA at 25°C, flows through R2 into the adjust pin. The output voltage can be calculated using the formula in Figure 2. 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 9 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U U W U APPLICATIONS INFORMATION IN VOUT OUT + VIN R2 LT1521 SHDN ADJ GND ) ) R1 VOUT = 3.75V 1 + R2 + (IADJ + R2) R1 VADJ = 3.75V IADJ = 50nA AT 25°C OUTPUT RANGE = 3.75V TO 20V LT1521 • F01 Figure 2. Adjustable Operation 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 positive temperature coefficient of approximately 15ppm/°C. The adjust pin bias current has a negative temperature coefficient. These effects will tend to cancel each other. 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 voltages 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 300mA is –20mV typical at VOUT = 3.75V. At VOUT = 12V, load regulation would be: 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 LT1521 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. For surface mount devices, heat sinking 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. The following tables list thermal resistance for each package. Measured values of thermal resistance for several different board sizes and copper areas are listed for each package. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper. All NC leads were connected to the ground plane. Table 1. MS8 Package COPPER AREA TOPSIDE** BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 110°C/W 1000mm2 2500mm2 2500mm2 115°C/W Thermal Considerations 225mm2 2500mm2 2500mm2 120°C/W The power handling capability of the device will be limited by the maximum rated junction temperature (125°C). The power dissipated by the device will be made up of two components: 100mm2 2500mm2 2500mm2 130°C/W (12V/3.75V)(– 20mV) = – 64mV 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) * Pin 4 is ground. ** Device is mounted on topside. Table 2. S8 Package* COPPER AREA TOPSIDE** BACKSIDE THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 60°C/W 1000mm2 2500mm2 2500mm2 60°C/W 225mm2 2500mm2 2500mm2 68°C/W 100mm2 2500mm2 2500mm2 74°C/W * Pins 3, 6, 7 are ground. ** Device is mounted on topside. 10 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U U W U APPLICATIONS INFORMATION Table 3. SOT-223 Package (Thermal Resistance Junction-to-Tab 20°C/W) COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 50°C/W 1000mm2 2500mm2 2500mm2 50°C/W 225mm2 2500mm2 2500mm2 58°C/W 100mm2 2500mm2 2500mm2 64°C/W 1000mm2 1000mm2 1000mm2 57°C/W 2 60°C/W 1000mm 2 0 1000mm is required to prevent oscillations. The LT1521 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 for larger load current deltas. Bypass capacitors, used to decouple individual components powered by the LT1521, will increase the effective value of the output capacitor. * Tab of device attached to topside copper. Calculating Junction Temperature Example: Given an output voltage of 3.3V, an input voltage range of 4.5V to 7V, an output current range of 0mA to 150mA and a maximum ambient temperature of 50°C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)) Where, IOUT(MAX) = 150mA VIN(MAX) = 7V IGND at (IOUT = 150mA, VIN = 7V) = 2.1mA So, P = 150mA(7V – 3.3V) + (2.1mA)(7V) = 0.57W If we use a SOT-223 package, then the thermal resistance will be in the range of 50°C/W to 65°C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 0.57W(60°C/W) = 34.2°C 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 + 34.2°C = 84.2°C Output Capacitance and Transient Performance The LT1521 is designed to be stable with a wide range of output capacitors. A minimum output capacitor of 1.5µF Protection Features The LT1521 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 temperatures should not exceed 125°C. The input of the device will withstand reverse voltages of 20V. 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 backward. For fixed voltage versions of the device, the output 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 20V. The output will act like an open circuit, no current will flow out of the pin. If the input is powered by 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. 11 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W U U APPLICATIONS INFORMATION 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 4 summarizes the following information. The reverse output current will follow the curve in Figure 3 when the input 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 on the LT1521 unconnected when the output is held high. This can happen when the LT1521 is powered from a TJ = 25°C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN VOUT = VSENSE (LT1521-3/LT1521-3.3 LT1521-5) VOUT = VADJ (LT1521) 45 40 35 30 25 5 LT1521 15 LT1521-3 10 LT1521-3.3 3 2 LT1521-3 LT1521-5 1 LT1521-5 5 0 VOUT = 3V (LT1521-3) VOUT = 3.3V (LT1521-3.3) VOUT = 5V (LT1521-5) 4 LT1521-3.3 20 When the input of the LT1521 is forced to a voltage below its nominal output voltage and its output is held high, the output current will follow the curve shown in Figure 3. This can happen if the input of the LT1521 is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or by 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 4). The state of the shutdown pin will have no effect on the reverse output current when the output is pulled above the input. INPUT CURRENT (µA) REVERSE OUTPUT CURRENT (µA) 50 rectified AC source. If the AC source is removed, then the input of the LT1521 is effectively left floating. The reverse output current also follows the curve in Figure 3 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. 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 0 0 1 3 2 INPUT VOLTAGE (V) LT1521 • F03 Figure 3. Reverse Output Current 12 4 5 LT1521 • F04 Figure 4. Input Current LT1521/LT1521-3 LT1521-3.3/LT1521-5 U W U U APPLICATIONS INFORMATION Table 4. Fault Conditions INPUT PIN SHDN PIN OUTPUT/SENSE PINS < VOUT (Nominal) Open (High) Forced to VOUT (Nominal) Reverse Output Current ≈ 5µA (See Figure 3) Input Current ≈ 1µA (See Figure 4) < VOUT (Nominal) Grounded Forced to VOUT (Nominal) Reverse Output Current ≈ 5µA (See Figure 3) Input Current ≈ 1µA (See Figure 4) Open Open (High) > 1V Reverse Output Current ≈ 5µA (See Figure 3) Open Grounded > 1V Reverse Output Current ≈ 5µA (See Figure 3) ≤ 0.8V Open (High) ≤ 0V Output Current = 0 ≤ 0.8V Grounded ≤ 0V Output Current = 0 > 1.5V Open (High) ≤ 0V Output Current = Short-Circuit Current – 20V < VIN < 20V Grounded ≤ 0V Output Current = 0 U PACKAGE DESCRIPTION RESULTING CONDITIONS Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0.118 ± 0.004** (3.00 ± 0.102) 0.192 ± 0.004 (4.88 ± 0.10) 1 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 2 3 4 0.034 ± 0.004 (0.86 ± 0.102) 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP 0.006 ± 0.004 (0.15 ± 0.102) MSOP (MS8) 1197 * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE 13 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 14 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP SO8 0996 LT1521/LT1521-3 LT1521-3.3/LT1521-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. ST Package 3-Lead Plastic SOT-223 (LTC DWG # 05-08-1630) 0.248 – 0.264 (6.30 – 6.71) 0.116 – 0.124 (2.95 – 3.15) 0.264 – 0.287 (6.71 – 7.29) 0.130 – 0.146 (3.30 – 3.71) 0.033 – 0.041 (0.84 – 1.04) 0.090 (2.29) NOM 10° – 16° 0.010 – 0.014 (0.25 – 0.36) 10° MAX 0.071 (1.80) MAX 10° – 16° 0.025 – 0.033 (0.64 – 0.84) 0.181 (4.60) NOM 0.012 (0.31) MIN 0.0008 – 0.0040 (0.0203 – 0.1016) 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. ST3 (SOT-233) 0792 15 LT1521/LT1521-3 LT1521-3.3/LT1521-5 RELATED PARTS PART NUMBER ® DESCRIPTION COMMENTS LTC 1174 425mA High Efficiency Step-Down Switching Regulator >90% Efficiency, SO-8 Package LT1175 500mA Micropower Low Dropout Negative Linear Regulator Selectable Current Limit LT1120A 125mA Micropower Low Dropout Linear Regulator 20µA Quiescent Current, Includes Comparator LT1304 Micropower Step-Up DC/DC Converter 15µA Quiescent Current, 1.5 Minimum Input LT1529 3A Micropower Low Dropout Regulator 50µA Quiescent Current 16 Linear Technology Corporation 1521335fa LT/TP 0299 REV A 2K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1995