19-1812; Rev 0; 1/01 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX The MAX1857 low-dropout linear regulator operates from a +2.5V to +5.5V supply and delivers a guaranteed 500mA load current with low 120mV dropout. The high-accuracy (±1%) output voltage is preset at an internally trimmed 4.75V or can be adjusted from 1.25V to 5.0V with an external resistive divider. An internal PMOS pass transistor allows the low 135µA supply current to remain independent of load, making this device ideal for portable battery-operated equipment such as personal digital assistants (PDAs), cellular phones, cordless phones, base stations, and notebook computers. Other features include an active-low open-drain reset output with a 4.5ms timeout period that indicates when the output is out of regulation, a 0.1µA shutdown mode, short-circuit protection, and thermal shutdown protection. The device is available in a miniature 8-pin µMAX package. For higher power applications, refer to the MAX1792 and MAX1793 data sheets. Features ♦ Guaranteed 500mA Output Current ♦ Low 120mV Dropout at 500mA ♦ Up to ±1% Output Voltage Accuracy Preset at 4.75V Adjustable from 1.25V to 5.0V ♦ Reset Output with 4.5ms Timeout Period ♦ Low 135µA Ground Current ♦ 0.1µA Shutdown Current ♦ Thermal Overload Protection ♦ Output Current Limit ♦ Tiny µMAX Package Ordering Information ________________________Applications Notebook Computers PART* Cellular and Cordless Telephones MAX1857EUA47 PDAs TEMP. RANGE PIN-PACKAGE -40°C to +85°C 8 µMAX *Contact factory for other preset output voltages. Palmtop Computers Base Stations USB Hubs Docking Stations Typical Operating Circuit VIN = +5V VOUT = 4.75V CIN 1µF IN NC OUT IN OUT COUT 3.3µF RRST 100k MAX1857 ON SHDN RST SET GND OFF Pin Configuration TOP VIEW IN 1 8 OUT IN 2 7 OUT 6 SET 5 GND RST TO µC 3 MAX1857 SHDN 4 µMAX ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX1857 General Description MAX1857 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX ABSOLUTE MAXIMUM RATINGS IN, SHDN, RST, SET to GND ....................................-0.3V to +6V OUT to GND ................................................-0.3V to (VIN + 0.3V) Output Short-Circuit Duration ........................................Indefinite Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.5mW/°C above +70°C) .............362mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Voltage Input Undervoltage Lockout SYMBOL CONDITIONS VIN VUVLO VOUT Adjustable Output Voltage Range 2.0 -1.5 +1.5 IOUT = 100mA, TA = 0°C to +85°C -2 +2 IOUT = 1mA to 500mA, VIN > VOUT + 0.5V, TA = 0°C to +85°C -3 +3 1.25 5 VIN = +2.7V, VOUT set to 2.0V, IOUT = 100mA TA = +85°C 1.229 TA = 0°C to +85°C 1.219 IOUT VIN ≥ 2.7V 500 Short-Circuit Current Limit ILIM VOUT = 0, VIN ≥ 2.7V 0.55 1.250 SET Dual Mode™ Threshold % % V 1.271 VSET = 1.25V 1.281 mARMS 1.2 2.2 2.0 50 100 -100 A A 150 mV +100 nA IOUT = 1mA 135 IOUT = 500mA 175 120 175 mV 0 +0.15 %/V 1.0 Dropout Voltage (Note 1) VIN VOUT IOUT = 500mA Line Regulation ∆VLNR VIN from (VOUT + 100mV) to 5.5V, ILOAD = 5mA Load Regulation ∆VLDR IOUT = 1mA to 500mA 0.4 10Hz to 1MHz, COUT = 3.3µF (ESR < 0.1Ω) 115 Output Voltage Noise UNITS V VOUT > 96% of nominal value, VIN ≥ 2.7V IQ V VOUT < 2.5V Maximum Output Current Ground-Pin Current V 2.3 +1 VSET ISET 5.5 2.15 -1 SET Voltage Threshold (Adjustable Mode) SET Input Bias Current MAX VOUT ≥ 2.5V VSET = 1.25V In-Regulation Current Limit TYP 2.5 Rising, 75mV hysteresis IOUT = 100mA, TA = +85°C Output Voltage Accuracy (Preset Mode) MIN -0.15 250 µA % µVRMS SHUTDOWN Shutdown Supply Current IOFF SHDN = GND, VIN = 5.5V SHDN Input Threshold VIH VIL 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V SHDN Input Bias Current SHDN = IN or GND 0.1 0.6 10 Dual Mode is a trademark of Maxim Integrated Products. 2 15 1.6 _______________________________________________________________________________________ 100 µA V nA 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX ((VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.01 0.1 V 5.5 V 100 nA RESET OUTPUT Reset Output Low Voltage VOL RST sinking 1mA Operating Voltage Range for Valid Reset RST sinking 100µA RST Output High Leakage Current V RST = +5.5V RST Threshold RST Release Delay tRP 1.0 Rising edge, referred to VOUT(NOMINAL) 83 86 89 % Rising edge of OUT to rising edge of RST 1.4 4.5 8 ms THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis TSHDN 170 °C ∆TSHDN 20 °C ELECTRICAL CHARACTERISTICS (VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER Input Voltage SYMBOL CONDITIONS VIN MIN MAX 2.5 5.5 UNITS V Input Undervoltage Lockout VUVLO Rising or falling 2.0 2.3 V Output Voltage Accuracy (Preset Mode) VOUT IOUT = 1mA to 500mA -3 +3 % VSET = 1.25V 1.25 5 V IOUT = 100mA 1.212 1.288 V Adjustable Output Voltage Range SET Voltage Threshold (Adjustable Mode) VSET Maximum Output Current IOUT Short-Circuit Current Limit ILIM VOUT = 0 0.55 ISET VSET = 1.25V IQ 500 A 50 150 mV -100 +100 nA IOUT = 1mA 250 µA 175 mV +0.15 %/V SET Dual Mode Threshold SET Input Bias Current Ground-Pin Current mARMS 2.2 Dropout Voltage (Note 1) VIN VOUT IOUT = 500mA Line Regulation ∆VLNR VIN from (VOUT + 100mV) to 5.5V, ILOAD = 5mA Load Regulation ∆VLDR IOUT = 1mA to 500mA 1.0 % 15 µA -0.15 SHUTDOWN Shutdown Supply Current IOFF SHDN = GND, VIN = +5.5V SHDN Input Threshold VIH 2.5V < VIN < 5.5V VIL 2.5V < VIN < 5.5V 0.6 SHDN = IN or GND 100 SHDN Input Bias Current 1.6 V nA _______________________________________________________________________________________ 3 MAX1857 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS 0.1 V 5.5 V 100 nA RESET OUTPUT Reset Output Low Voltage RST sinking 1mA VOL Operating Voltage Range for Valid Reset RST sinking 100µA RST Output High Leakage Current V RST = +5.5V RST Threshold Rising edge, referred to VOUT(NOMINAL) 83 89 % Rising edge of OUT to rising edge of RST 1.4 8 ms RST Release Delay tRP 1.0 Note 1: Dropout voltage is defined as VIN - VOUT, when VOUT is 100mV below the value of VOUT measured when VIN = VOUT(NOM) + 0.5V. Since the minimum input voltage is 2.5V, this specification is only meaningful when VOUT(NOM) ≥ 2.5V. For VOUT(NOM) between 2.5V and 3.5V, use the following equations: Typical Dropout = -93mV/V ✕ VOUT(NOM) + 445mV; Guaranteed Maximum Dropout = -137mV/V ✕ VOUT(NOM) + 704mV. For VOUT(NOM) ≥ 3.5V: Typical Dropout = 120mV; Guaranteed Maximum Dropout = 175mV. Note 2: Specifications to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, CIN = 1µF, COUT = 3.3µF, TA = +25°C, unless otherwise noted.) 4.72 VIN = 5.00V 4.76 4.74 4.72 4.64 200 400 600 OUTPUT CURRENT (mA) 800 1000 TA = +85°C 250 TA = +25°C 200 150 100 TA = -40°C 50 0 4.70 0 300 MAX1857 toc02 4.78 OUTPUT VOLTAGE (V) VIN = 5.25V IOUT = 0mA DROPOUT VOLTAGE (mV) 4.76 4.68 4 4.80 MAX1857 toc01 4.80 DROPOUT VOLTAGE vs. OUTPUT CURRENT OUTPUT VOLTAGE vs. TEMPERATURE MAX1857 toc03 OUTPUT VOLTAGE vs. OUTPUT CURRENT OUTPUT VOLTAGE (V) MAX1857 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX -55 -25 5 35 65 TEMPERATURE (°C) 95 125 0 200 400 600 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 800 1000 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX1857 toc04 COUT = 3.3µF IOUT = 50mA 70 PSRR (dB) LOAD-TRANSIENT RESPONSE MAX1857 toc05 80 4.80V 60 4.75V 50 4.70V 40 600mA 30 400mA 20 200mA 10 0 A B 0 0.01 0.1 1 10 100 1000 10µs/div A: VOUT = 4.75V, 50mV/div B: IOUT = 5mA TO 500mA, 200mA/div VIN = 5.25V, CIN = 10µF FREQUENCY (kHz) SWITCHING POWER-SUPPLY RIPPLE REJECTION LOAD-TRANSIENT RESPONSE NEAR DROPOUT MAX1857 toc07 MAX1857 toc06 4.80V 4.75V A 5.0V A B 4.75V B 4.70V 4.65V 400mA 200mA 0 2µs/div A: MAX1632: VIN = 9V, VOUT = 5.0V, 20mV/div B: MAX1857: VOUT = 4.75V, IOUT = 500mA, 2mV/div OUTMAX1632 = INMAX1857 10µs/div A: VOUT = 4.75V, 50mV/div B: IOUT = 5mA TO 500mA, 200mA/div VIN = VOUT + 100mV = 4.85V, CIN = 10µF RST WAVEFORM SHUTDOWN WAVEFORM MAX1857 toc09 MAX1857 toc08 2V A A 1V 0 0 B 6V 0 4V 2V B C 0 0 40µs/div A: VSHDN = 0 TO 2V, 1V/div B: VOUT = 4.75V, 2V/div ROUT = 9.5Ω (500mA) 20ms/div A: VIN = 0 TO 5.5V, 2V/div B: VOUT = 4.75V, ROUT = 95Ω, 2V/div C: VRST, 100kΩ TO OUT, 2V/div _______________________________________________________________________________________ 5 MAX1857 Typical Operating Characteristics (continued) (VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, CIN = 1µF, COUT = 3.3µF, TA = +25°C, unless otherwise noted.) MAX1857 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX Pin Description PIN NAME FUNCTION 1, 2 IN Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with a 1µF capacitor or greater to GND (see Capacitor Selection and Regulator Stability). Connect both input pins together externally. 3 RST Open-Drain, Active-Low Reset Output. RST remains low while the output voltage (VOUT) is below the reset threshold and for at least 4ms after VOUT rises above the reset threshold. Connect a 100kΩ pullup resistor to OUT. 4 SHDN 5 GND Ground 6 SET Voltage-Setting Input. Connect to GND for preset output. Connect a resistive voltage-divider from OUT to set the output voltage between 1.25V and 5.0V. 7, 8 OUT Regulator Output. Sources up to 500mA. Bypass with a 3.3µF low-ESR capacitor to GND. Use a 4.7µF capacitor for output voltages below 2V. Connect both output pins together. Active-Low Shutdown Input. A logic low reduces supply current to 0.1µA. In shutdown, the RST output is low and OUT is pulled low through an internal 5kΩ resistor. Connect to IN for normal operation. VIN = +2.5V TO +5.5V IN CIN 1µF IN THERMAL SENSOR MOSFET DRIVER WITH I LIM OUT ON VOUT = 1.25V TO 5.0V SHDN COUT 3.3µF OUT OFF SHUTDOWN LOGIC 5kΩ VREF 1.25V ERROR AMPLIFIER LOGIC SUPPLY VOLTAGE (VOUT) RRST 100kΩ TO µC R1 MAX1857 RST SET DELAY TIMER R2 86% VREF 100mV GND Figure 1. Functional Diagram 6 _______________________________________________________________________________________ 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX MAX1857 Detailed Description The MAX1857 is a low-dropout, low-quiescent-current ripple rejector designed primarily for audio and video applications. The device supplies loads up to 500mA and is available with a preset output voltage of 4.75V. As shown in Figure 1, the MAX1857 consists of a 1.25V reference, error amplifier, P-channel pass transistor, and internal feedback voltage-divider. The 1.25V reference is connected to the error amplifier, which compares this reference with the feedback voltage and amplifies the difference. If the feedback voltage is lower than the reference voltage, the pass-transistor gate is pulled lower, which allows more current to pass to the output and increases the output voltage. If the feedback voltage is too high, the passtransistor gate is pulled up, allowing less current to pass to the output. The output voltage is fed back through either an internal resistive divider connected to OUT or an external resistor network connected to SET. The dual-mode comparator examines VSET and selects the feedback path. If VSET is below 50mV, the internal feedback path is used and the output is regulated to the factory-preset voltage. Additional blocks include an output current limiter, reset comparator, thermal sensor, and shutdown logic. Internal P-Channel Pass Transistor The MAX1857 features a 0.25Ω P-channel MOSFET pass transistor. Unlike similar designs using PNP pass transistors, P-channel MOSFETs require no base drive, which reduces quiescent current. PNP-based regulators also waste considerable current in dropout when the pass transistor saturates, and use high base-drive currents under large loads. The MAX1857 does not suffer from these problems and consumes only 175µA of quiescent current under heavy loads as well as in dropout. Output Voltage Selection The MAX1857’s dual-mode operation allows operation in either a preset voltage mode or an adjustable mode. Connect SET to GND to select the preset output voltage. The two-digit part number suffix identifies the output voltage (see Selector Guide). For example, the MAX1857EUA47 has a preset 4.75V output voltage. The output voltage may also be adjusted by connecting a voltage-divider from OUT to SET (Figure 2). Select R2 R1 = R2 IN OUT IN OUT VOUT 1.25V V IN = +2.5V TO +5.5V -1 VOUT CIN 1µF COUT 3.3µF MAX1857 R1 ON SHDN SET OFF R2 RST GND Figure 2. Adjustable Output Using External Feedback Resistors in the 25kΩ to 100kΩ range. Calculate R1 with the following equation: R1 = R2 [(VOUT / VSET) – 1] where VSET = 1.25V, and VOUT may range from 1.25V to 5.0V. Shutdown Pull SHDN low to enter shutdown. During shutdown, the output is disconnected from the input and supply current drops to 0.1µA. When in shutdown, RST pulls low and OUT is discharged through an internal 5kΩ resistor. The capacitance and load at OUT determine the rate at which VOUT decays. SHDN can be pulled as high as 6V, regardless of the input and output voltage. Reset Output The reset output (RST) pulls low when OUT is less than 86% of the nominal regulation voltage. Once OUT exceeds 86% of the nominal voltage, RST goes high impedance after 4.5ms. RST is an open-drain N-channel output. To obtain a voltage at RST, connect a pullup resistor from RST to OUT. A 100kΩ resistor works well for most applications. RST can be used as a power-on-reset (POR) signal to a microcontroller (µC), or drive an external LED to indicate power failure. When the MAX1857 is _______________________________________________________________________________________ 7 shut down, RST is held low independent of the output voltage. If unused, leave RST grounded or unconnected. 0.7 Current Limit 0.6 Thermal Overload Protection Thermal overload protection limits total power dissipation in the MAX1857. When the junction temperature exceeds TJ = +170°C, a thermal sensor turns off the pass transistor, allowing the device to cool. The thermal sensor turns the pass transistor on again after the junction temperature cools by 20°C, resulting in a pulsed output during continuous thermal overload conditions. Thermal overload protection protects the MAX1857 in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction-temperature rating of TJ = +150°C. Operating Region and Power Dissipation The MAX1857’s maximum power dissipation depends on the thermal resistance of the IC package and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated in the device is P = IOUT x (VIN - VOUT). The maximum allowed power dissipation is 330mW or: PMAX = (TJ(MAX) - TA) / ( θJC + θCA) where TJ - TA is the temperature difference between the MAX1857 die junction and the surrounding air; θJC is the thermal resistance from the junction to the case; and θ CA is the thermal resistance from the case through the PC board, copper traces, and other materials to the surrounding air. The MAX1857 delivers up to 0.5ARMS and operates with input voltages up to 5.5V, but not simultaneously. High output currents can only be sustained when input-output differential voltages are low, as shown in Figure 3. Applications Information Capacitor Selection and Regulator Stability Capacitors are required at the MAX1857’s input and output for stable operation over the full temperature range and with load currents up to 500mA. Connect a 1µF capacitor between IN and ground and a 3.3µF low 8 CONTINUOUS CURRENT LIMIT 0.5 TA = +50°C TYPICAL VDROPOUT LIMIT The MAX1857 monitors and controls the pass transistor’s gate voltage, limiting the output current to 1.2A. This current limit doubles when the output voltage is within 4% of the nominal value to improve performance with large load transients. The output can be shorted to ground for an indefinite period of time without damaging the part. µMAX PACKAGE OPERATING REGION AT TJ(MAX) = +150°C MAXIMUM OUTPUT CURRENT (A) MAX1857 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX 0.4 0.3 0.2 TA = +70°C MAXIMUM SUPPLY VOLTAGE LIMIT (VOUT = 1.25V) TA = +85°C 0.1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT-OUTPUT VOLTAGE DIFFERENTIAL (V) Figure 3. Power Operating Regions: Maximum Output Current vs. Supply Voltage equivalent series resistance (ESR) capacitor between OUT and ground. For output voltages less than 2V, use a 4.7µF low-ESR output capacitor. The input capacitor (CIN) lowers the source impedance of the input supply. Reduce noise and improve load-transient response, stability, and power-supply rejection by using larger output capacitors such as 10µF. The output capacitor’s (COUT) ESR affects stability and output noise. Use output capacitors with an ESR of 0.1Ω or less to ensure stability and optimum transient response. Surface-mount ceramic capacitors have very low ESR and are commonly available in values up to 10µF. Connect CIN and COUT as close to the MAX1857 as possible to minimize the impact of PC board trace inductance. Noise, PSRR, and Transient Response The MAX1857 is designed to operate with low dropout voltages and low quiescent currents in battery-powered systems while still maintaining good noise, transient response, and AC rejection. See the Typical Operating Characteristics for a plot of power-supply rejection ratio (PSRR) vs. frequency. When operating from noisy sources, improved supply-noise rejection and transient response can be achieved by increasing the values of the input and output bypass capacitors and through passive filtering techniques. The MAX1857 load-transient response graphs (see Typical Operating Characteristics) show two compo- _______________________________________________________________________________________ 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX Chip Information TRANSISTOR COUNT: 845 Input-Output (Dropout) Voltage A regulator’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the MAX1857 uses a P-channel MOSFET pass transistor, its dropout voltage is a function of drain-tosource on-resistance (RDS(ON)) multiplied by the load current (see Typical Operating Characteristics): VDROPOUT = VIN - VOUT = RDS(ON) x IOUT The MAX1857 ground current remains below 150µA in dropout. _______________________________________________________________________________________ 9 MAX1857 nents of the output response: a DC shift from the output impedance due to the load current change, and the transient response. A typical transient response for a step change in the load current from 5mA to 500mA is 18mV. Increasing the output capacitor’s value and decreasing the ESR attenuates the overshoot. MAX1857 500mA, Low-Dropout, Ripple-Rejecting LDO in µMAX 8LUMAXD.EPS Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.