LTC3025-3

LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 500mA Micropower VLDO Linear Regulators FeaTures n n n n n DescripTion The LTC®3025-X is a micropower, VLDO™ (very low dropout) linear regulator which operates from input voltages as low as 0.9V. The device is capable of supplying 500mA of output current with a typical dropout voltage of only 85mV. A BIAS supply is required to run the internal reference and LDO circuitry while output current comes directly from the IN supply for high efficiency regulation. The LTC3025-1 features an adjustable output with a low 0.4V reference while the LTC3025-2, LTC3025-3, and LTC3025-4 have fixed 1.2V, 1.5V and 1.8V output voltages respectively. The LTC3025-X’s low quiescent current makes it an ideal choice for use in battery-powered systems. For 3-cell NiMH and single cell Li-Ion applications, the BIAS voltage can be supplied directly from the battery while the input can come from a high efficiency buck regulator, providing a high efficiency, low noise output. Other features include high output voltage accuracy, excellent transient response, stability with ultralow ESR ceramic capacitors as small as 1µF short-circuit and , thermal overload protection and output current limiting. The LTC3025-X is available in a tiny, low profile (0.75mm) 6-lead DFN (2mm × 2mm) package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and VLDO and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 7224204, 7218082. n n n n n n n n n n Wide Input Voltage Range: 0.9V to 5.5V Stable with Ceramic Capacitors Very Low Dropout: 85mV at 500mA Adjustable Output Range: 0.4V to 3.6V (LTC3025-1) Fixed Output: 1.2V (LTC3025-2), 1.5V (LTC3025-3), 1.8V (LTC3025-4) ±2% Voltage Accuracy over Temperature, Supply and Load Low Noise: 80µVRMS (10Hz to 100kHz) BIAS Voltage Range: 2.5V to 5.5V Fast Transient Recovery Shutdown Disconnects Load from VIN and VBIAS Low Operating Current: IIN = 4µA, IBIAS = 50µA Typ Low Shutdown Current: IIN = 1µA, IBIAS = 0.01µA Typ Output Current Limit Thermal Overload Protection Available in 6-Lead (2mm × 2mm) DFN Package applicaTions n n n n n n n Low Power Handheld Devices Low Voltage Logic Supplies DSP Power Supplies Cellular Phones Portable Electronic Equipment Handheld Medical Instruments Post Regulator for Switching Supply Noise Rejection Typical applicaTion 1.2V Output Voltage from 1.5V Input Supply BIAS Li-Ion OR 3-CELL NiMH 1.5V HIGH EFFICIENCY 1.5V DC/DC BUCK 0.1µF IN 0.1µF OFF ON SHDN GND 30251234 TA01 1MHz VIN Supply Rejection 50 45 VOUT = 1.2V IOUT ≤ 500mA REJECTION (dB) COUT = 10µF COUT = 1µF OUT 1µF 40 35 30 25 20 15 10 5 BIAS = 3.6V VOUT = 1.2V 0 1.2 1.4 1.6 IOUT = 100mA IOUT = 300mA 1.8 2.0 VIN (V) 2.2 2.4 2.6 LTC3025-2 SENSE 30251234 TA01b 30251234ff 1 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 absoluTe MaxiMuM raTings (Notes 1, 2) pin conFiguraTion TOP VIEW BIAS 1 GND 2 IN 3 7 6 SHDN 5 ADJ/SENSE* 4 OUT VBIAS, VIN to GND......................................... –0.3V to 6V SHDN to GND............................................... –0.3V to 6V SENSE, ADJ to GND ..................................... –0.3V to 6V VOUT ........................................–0.3V to VIN + 0.3V or 6V Operating Junction Temperature Range (Note 3).................................................. –40°C to 125°C Storage Temperature Range................... –65°C to 125°C Output Short-Circuit Duration .......................... Indefinite DC6 PACKAGE 6-LEAD (2mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 102°C/W, θJC = 20°C/W EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB *ADJ FOR LTC3025-1, SENSE FOR LTC3025-2, LTC3025-3, LTC3025-4 orDer inForMaTion LEAD FREE FINISH LTC3025EDC-1#PBF LTC3025IDC-1#PBF LTC3025EDC-2#PBF LTC3025IDC-2#PBF LTC3025EDC-3#PBF LTC3025IDC-3#PBF LTC3025EDC-4#PBF LTC3025IDC-4#PBF LEAD BASED FINISH LTC3025EDC-1 LTC3025IDC-1 LTC3025EDC-2 LTC3025IDC-2 LTC3025EDC-3 LTC3025IDC-3 LTC3025EDC-4 LTC3025IDC-4 TAPE AND REEL LTC3025EDC-1#TRPBF LTC3025IDC-1#TRPBF LTC3025EDC-2#TRPBF LTC3025IDC-2#TRPBF LTC3025EDC-3#TRPBF LTC3025IDC-3#TRPBF LTC3025EDC-4#TRPBF LTC3025IDC-4#TRPBF TAPE AND REEL LTC3025EDC-1#TR LTC3025IDC-1#TR LTC3025EDC-2#TR LTC3025IDC-2#TR LTC3025EDC-3#TR LTC3025IDC-3#TR LTC3025EDC-4#TR LTC3025IDC-4#TR PART MARKING* LDDW LDDW LDMK LDMK LDQS LDQS LDPQ LDPQ PART MARKING* LDDW LDDW LDMK LDMK LDQS LDQS LDPQ LDPQ PACKAGE DESCRIPTION 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN PACKAGE DESCRIPTION 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN 6-Lead (2mm × 2mm) Plastic DFN TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 30251234ff 2 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 elecTrical characTerisTics PARAMETER VIN Operating Voltage (Note 4) CONDITIONS LTC3025-1 LTC3025-2 LTC3025-3 LTC3025-4 VBIAS Operating Voltage (Note 4) LTC3025-1 LTC3025-2 LTC3025-3 LTC3025-4 VBIAS Undervoltage Lockout VIN Operating Current VIN Operating Current VBIAS Operating Current VBIAS Operating Current VIN Shutdown Current VBIAS Shutdown Current VADJ Regulation Voltage (Note 5) VSENSE Regulation Voltage (Note 5) VSENSE Regulation Voltage (Note 5) VSENSE Regulation Voltage (Note 5) IADJ ADJ Input Current OUT Load Regulation IOUT = 10µA, VOUT = 1.2V, LTC3025-1 IOUT = 0µA, LTC3025-2/LTC3025-3/LTC3025-4 IOUT = 10µA, VOUT = 1.2V, LTC3025-1 IOUT = 0µA, LTC3025-2/LTC3025-3/LTC3025-4 VSHDN = 0V VSHDN = 0V 1mA ≤ IOUT ≤ 500mA, VOUT = 1.2V, 1.5V ≤ VIN ≤ 5V, LTC3025-1 1mA ≤ IOUT ≤ 500mA, VOUT = 1.2V, 1.5V ≤ VIN ≤ 5V, LTC3025-1 1mA ≤ IOUT ≤ 500mA, 1.5V ≤ VIN ≤ 5V, LTC3025-2 1mA ≤ IOUT ≤ 500mA, 1.5V ≤ VIN ≤ 5V, LTC3025-2 1mA ≤ IOUT ≤ 500mA, 1.7V ≤ VIN ≤ 5V, LTC3025-3 1mA ≤ IOUT ≤ 500mA, 1.7V ≤ VIN ≤ 5V, LTC3025-3 1mA ≤ IOUT ≤ 500mA, 2.0V ≤ VIN ≤ 5V, LTC3025-4 1mA ≤ IOUT ≤ 500mA, 2.0V ≤ VIN ≤ 5V, LTC3025-4 VADJ = 0.45V, LTC3025-1 ∆IOUT = 1mA to 500mA, LTC3025-2 ∆IOUT = 1mA to 500mA, LTC3025-3 ∆IOUT = 1mA to 500mA, LTC3025-4 VIN = 1.5V to 5V, VBIAS = 3.6V, VOUT = 1.2V, IOUT = 1mA, LTC3025-1 VIN = 1.5V to 5V, VBIAS = 3.6V, IOUT = 1mA, LTC3025-2 VIN = 1.8V to 5V, VBIAS = 3.6V, IOUT = 1mA, LTC3025-3 VIN = 2.1V to 5V, VBIAS = 3.6V, IOUT = 1mA, LTC3025-4 VIN = 1.5V, VBIAS = 2.7V to 5V, VOUT = 1.2V, IOUT = 1mA, LTC3025-1 VIN = 1.5V, VBIAS = 2.7V to 5V, IOUT = 1mA, LTC3025-2 VIN = 1.8V, VBIAS = 3.0V to 5V, IOUT = 1mA, LTC3025-3 VIN = 2.1V, VBIAS = 3.3V to 5V, IOUT = 1mA, LTC3025-4 VBIAS = 3V, VIN = 1.5V, IOUT = 500mA, VADJ = 0.37V(LTC3025-1), VSENSE = 1.15V(LTC3025-2) VBIAS = 3.1V, VIN = 1.7V, IOUT = 500mA, VSENSE = 1.45V(LTC3025-3) VBIAS = 3.4V, VIN = 2.0V, IOUT = 500mA, VSENSE = 1.75V(LTC3025-4) LTC3025-1 l l l l l l l l l l l l l l l l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V, VBIAS = 3.6V, COUT = 1µF CIN = 0.1µF CBIAS = 0.1µF , , (all capacitors ceramic) unless otherwise noted. (Note 3) MIN 0.9 1.4 1.7 2.0 2.5 2.7 3.0 3.3 2.2 4 4 50 50 1 0.01 0.395 0.392 1.185 1.176 1.481 1.470 1.777 1.764 –50 0.4 0.4 1.2 1.2 1.5 1.5 1.8 1.8 0 –0.35 –1 –1.3 –1.5 0.07 0.21 0.26 0.32 4.5 4.5 4.5 4.5 85 90 l TYP MAX 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 2.5 10 10 80 80 5 1 0.405 0.408 1.215 1.224 1.519 1.530 1.823 1.836 50 UNITS V V V V V V V V V µA µA µA µA µA µA V V V V V V V V nA mV mV mV mV mV mV mV mV OUT Load Regulation (Referred to ADJ Pin) ∆IOUT = 1mA to 500mA, LTC3025-1 VIN Line Regulation (Referred to ADJ Pin) VIN Line Regulation VBIAS Line Regulation VBIAS Line Regulation VIN to VOUT Dropout Voltage (Notes 4, 6) VIN to VOUT Dropout Voltage (Notes 4, 6) VIN to VOUT Dropout Voltage (Notes 4, 6) VBIAS to VOUT Dropout Voltage (Note 4) 16.5 16.5 16.5 16.5 120 170 130 185 130 185 1.5 mV mV mV mV mV mV mV mV mV mV V 30251234ff 90 l l 3 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V, VBIAS = 3.6V, COUT = 1µF CIN = 0.1µF CBIAS = 0.1µF , , (all capacitors ceramic) unless otherwise noted. (Note 3) PARAMETER IOUT Continuous Output Current IOUT Current Limit en Output Voltage Noise VIH SHDN Input High Voltage VIL SHDN Input Low Voltage IIH SHDN Input High Current IL SHDN Input Low Current SHDN = 1.2V SHDN = 0V VADJ = 0V(LTC3025-1), VSENSE = 0V(LTC3025-2/LTC3025-3/LTC3025-4) f = 10Hz to 100kHz, IOUT = 300mA l l elecTrical characTerisTics CONDITIONS MIN l TYP 1130 80 MAX UNITS mA mA µVRMS V 500 0.9 0.3 –1 –1 1 1 V µA µA 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. Note 2: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: The LTC3025-X regulators are tested and specified under pulse load conditions such that TJ ≈ TA. The LTC3025E-X are guaranteed to meet performance specifications from 0°C and 125°C. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3025I-X are guaranteed to meet performance specifications over the full –40°C to 125°C operating junction temperature range. Note 4: For the LTC3025-1, a regulated output voltage will only be available when the minimum IN and BIAS operating voltages as well as the IN to OUT and BIAS to OUT dropout voltages are all satisfied. For the LTC3025-2/LTC3025-3/LTC3025-4 the minimum IN operating voltage assumes IOUT = 500mA. For correct regulation at IOUT < 500mA the minimum IN operating voltage decreases to the maximum VSENSE Regulation Voltage as IOUT decreases to 0mA (i.e. VINMIN = 1.312V at IOUT = 250mA for the LTC3025-2). Note 5: 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 6: Dropout voltage is minimum input to output voltage differential needed to maintain regulation at a specified output current. In dropout, the output voltage will be equal to VIN – VDROPOUT. 30251234ff 4 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 Typical perForMance characTerisTics VIN to VOUT Dropout Voltage vs IOUT 120 100 DROPOUT VOLTAGE (mV) 80 60 40 20 0 TA = –40°C VBIAS = 2.8V VIN = 1.4V TA = 125°C TA = 25°C IBIAS (µA) 500 450 400 350 125°C 25°C –40°C IBIAS (µA) 300 250 200 150 100 50 0 50 100 150 200 250 300 350 400 450 500 IOUT (mA) 30251234 G01 (TA = 25°C unless otherwise noted) Operating BIAS Current vs Output Current 80 BIAS No Load Operating Current VIN = 1.5V 70 VOUT = 1.2V 60 50 40 30 20 10 125°C –40°C 25°C 0 0.01 0.1 1 10 IOUT (mA) 100 1000 0 2.5 3 3.5 4.5 4 VBIAS (V) 5 5.5 30251234 G02 30251234 G03 VIN No Load Operating Current 14 12 10 IIN (µA) 8 6 4 2 0 0.5 1.5 2.5 3.5 4.5 5.5 VBIAS = 5V VOUT = 0.8V 7 6 125°C 85°C 25°C –40°C IIN (µA) 5 4 3 2 1 VIN Shutdown Current VBIAS = 5V 405 404 403 ADJUST VOLTAGE (mV) 402 401 400 399 398 397 396 1.5 2.5 3.5 4.5 5.5 –40°C Adjust Voltage vs Temperature VBIAS = 3.6V VIN = 1.5V IOUT = 10µA 25°C 85°C 0 0.5 395 –50 –25 VIN (V) 30251234 G04 VIN (V) 30251234 G05 50 25 0 75 TEMPERATURE (°C) 100 125 30251234 G06 SHDN Threshold vs Temperature 1000 900 800 SHDN THRESHOLD (mV) 700 600 500 400 300 200 100 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 VBIAS = 2.5V VBIAS = 5V CURRENT LIMIT (mA) 1600 1400 1200 1000 800 600 400 200 0 Current Limit vs VIN Voltage VIN AC 100mV/DIV Burst Mode DC/DC Buck Ripple Rejection VOUT AC 10mV/DIV 0 1 2 3 VIN (V) 4 5 6 VIN = 1.8V VOUT = 1.5V COUT = 1µF IOUT = 50mA 10µs/DIV 30251234 G09 30251234 G07 30251234 G08 30251234ff 5 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 Typical perForMance characTerisTics VIN Ripple Rejection vs Frequency 70 60 50 40 30 20 10 VBIAS = 3.6V VIN = 1.5V VOUT = 1.2V IOUT = 100mA 1k 10k 100k 1M 10M FREQUENCY (Hz) 30251234 G10 (TA = 25°C unless otherwise noted) BIAS Ripple Rejection vs Frequency 70 50 45 COUT = 10µF REJECTION (dB) 40 35 30 25 20 15 10 60 50 40 30 20 10 COUT = 1µF VBIAS = 3.6V VIN = 1.5V VOUT = 1.2V IOUT = 100mA 1k 10k 100k 1M 10M FREQUENCY (Hz) 30251234 G11 3MHz VIN Supply Rejection COUT = 10µF COUT = 1µF COUT = 10µF REJECTION (dB) REJECTION (dB) COUT = 1µF 0 100 0 100 5 VBIAS = 3.6V VOUT = 1.2V 0 1.2 1.4 1.6 IOUT = 100mA IOUT = 300mA 1.8 2.0 VIN (V) 2.2 2.4 2.6 30251234 G12 Transient Response 0.300 IOUT 250mA 10mA VIN to VOUT Dropout Voltage vs VIN (25°C) LTC3025-1 BIAS = 2.7V 0.300 0.275 0.250 0.225 DROPOUT (V) 0.200 0.175 0.150 0.125 0.100 0.075 0.050 0.025 0 VIN to VOUT Dropout Voltage vs VIN (90°C) LTC3025-1 0.275 0.250 0.225 DROPOUT (V) 0.200 0.175 0.150 0.125 0.100 0.075 VIN = 1.5V VOUT = 1.2V VBIAS = 3.6V COUT = 1µF 100µs/DIV 30251234 G13 BIAS = 3V BIAS = 3.3V VOUT AC 10mV/DIV BIAS = 3.8V BIAS = 5V VADJ = 0.385 IOUT = 500mA TA = 25°C 1 1.5 2 3 2.5 VIN (V) 3.5 4 4.5 BIAS = 3.8V BIAS = 5V BIAS = 3.3V VADJ = 0.385 BIAS = 3V IOUT = 500mA BIAS = 2.7V TA = 90°C 1 1.5 2 3 2.5 VIN (V) 3.5 4 4.5 0.050 0.025 0 30251234 G14 30251234 G15 30251234ff 6 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 pin FuncTions BIAS (Pin 1): BIAS Input Voltage. BIAS provides internal power for LTC3025-X circuitry. The BIAS pin should be locally bypassed to ground if the LTC3025-X is more than a few inches away from another source of bulk capacitance. In general, the output impedance of a battery rises with frequency, so it is usually advisable to include an input bypass capacitor in battery-powered circuits. A capacitor in the range of 0.01µF to 0.1µF is usually sufficient. GND (Pin 2): Ground. Connect to a ground plane. IN (Pin 3): Input Supply Voltage. The output load current is supplied directly from IN. The IN pin should be locally bypassed to ground if the LTC3025-X is more than a few inches away from another source of bulk capacitance. In general, the output impedance of a battery rises with frequency, so it is usually advisable to include an input bypass capacitor when supplying IN from a battery. A capacitor in the range of 0.1µF to 1µF is usually sufficient. OUT (Pin 4): Regulated Output Voltage. The OUT pin supplies power to the load. A minimum ceramic output capacitor of at least 1µF is required to ensure stability. Larger output capacitors may be required for applications with large transient loads to limit peak voltage transients. See the Applications Information section for more information on output capacitance. ADJ (Pin 5) LTC3025-1: Adjust Input. This is the input to the error amplifier. The ADJ pin reference voltage is 0.4V referenced to ground. The output voltage range is 0.4V to 3.6V and is typically set by connecting ADJ to a resistor divider from OUT to GND. See Figure 2. SENSE (Pin 5) LTC3025-2, LTC3025-3, LTC3025-4: Output Sense. The sense is the input to the resistor divider driving the error amplifier. Optimum regulation will be obtained at the point where SENSE is connected to OUT. The SENSE pin bias current is 10µA at the nominal rated output voltage. SHDN (Pin 6): Shutdown Input, Active Low. This pin is used to put the LTC3025-X into shutdown. The SHDN pin current is typically less than 10nA. The SHDN pin cannot be left floating and must be tied to a valid logic level (such as BIAS) if not used. GND (Exposed Pad Pin 7): Ground and Heat Sink. Must be soldered to PCB ground plane or large pad for optimal thermal performance. block DiagraM LTC3025-1 BIAS BIAS LTC3025-2, LTC3025-3, LTC3025-4 1 1 6 SHDN REFERENCE SHDN 0.4V SOFT-START IN + – 6µA 3 6 SHDN REFERENCE SHDN 0.4V SOFT-START IN + – 6µA 3 2 GND OUT ADJ 4 5 2 GND R1 40k R2 80k (LTC3025-2) 110k (LTC3025-3) 140k (LTC3025-4) OUT SENSE 4 5 30251234 BD 30251234ff 7 LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4 applicaTions inForMaTion Operation (Refer to Block Diagram) The LTC3025-X is a micropower, VLDO (very low dropout) linear regulator which operates from input voltages as low as 0.9V. The device provides a highly accurate output that is capable of supplying 500mA of output current with a typical dropout voltage of only 85mV. A single ceramic capacitor as small as 1µF is all that is required for output bypassing. A low reference voltage allows the LTC3025-1 output to be programmed to much lower voltages than available in common LDOs (range of 0.4V to 3. 6V). The LTC3025-2/LTC3025-3/LTC3025-4 have fixed outputs of 1.2V, 1.5V and 1.8V respectively, eliminating the need for an external resistor divider. As shown in the Block Diagram, the BIAS input supplies the internal reference and LDO circuitry while all output current comes directly from the IN input for high efficiency regulation. The low quiescent supply currents IIN = 4µA, IBIAS = 50µA drop to IIN = 1µA, IBIAS = 0.01µA typical in shutdown making the LTC3025-X an ideal choice for use in battery-powered systems. The device includes current limit and thermal overload protection. The fast transient response of the follower output stage overcomes the traditional tradeoff between dropout voltage, quiescent current and load transient response inherent in most LDO regulator architectures. The LTC3025-X also includes overshoot detection circuitry which brings the output back into regulation when going from heavy to light output loads (see Figure 1). 300mA 0mA Adjustable Output Voltage (LTC3025-1) The output voltage is set by the ratio of two external resistors as shown in Figure 2. The device servos the output to maintain the ADJ pin voltage at 0.4V (referenced to ground). Thus, the current in R1 is equal to 0.4V/R1. For good transient response, stability, and accuracy, the current in R1 should be at least 8µA, thus the value of R1 should be no greater than 50k. The current in R2 is the current in R1 plus the ADJ pin bias current. Since the ADJ pin bias current is typically