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19-1812; Rev 0; 1/01
500mA, Low-Dropout, Ripple-Rejecting LDO in MAX
General Description
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 135A 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 0.1A shutdown mode, short-circuit protection, and thermal shutdown protection. The device is available in a miniature 8-pin MAX package. For higher power applications, refer to the MAX1792 and MAX1793 data sheets. o Guaranteed 500mA Output Current o Low 120mV Dropout at 500mA o Up to 1% Output Voltage Accuracy Preset at 4.75V Adjustable from 1.25V to 5.0V o Reset Output with 4.5ms Timeout Period o Low 135A Ground Current o 0.1A Shutdown Current o Thermal Overload Protection o Output Current Limit o Tiny MAX Package
Features
MAX1857
________________________Applications
Notebook Computers Cellular and Cordless Telephones PDAs Palmtop Computers Base Stations USB Hubs Docking Stations
PART* MAX1857EUA47
Ordering Information
TEMP. RANGE -40C to +85C PIN-PACKAGE 8 MAX
*Contact factory for other preset output voltages.
Typical Operating Circuit
VIN = +5V IN NC CIN 1F IN OUT OUT COUT 3.3F IN 1 IN 2 RST TO C 3 VOUT = 4.75V
Pin Configuration
TOP VIEW
8 7
OUT OUT SET GND
MAX1857
ON SHDN OFF RST
RRST 100k
MAX1857
6 5
SHDN 4
SET
GND
MAX
________________________________________________________________ Maxim Integrated Products
1
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
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 = +70C) 8-Pin MAX (derate 4.5mW/C above +70C) .............362mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Input Voltage Input Undervoltage Lockout SYMBOL VIN VUVLO Rising, 75mV hysteresis IOUT = 100mA, TA = +85C Output Voltage Accuracy (Preset Mode) VOUT VOUT 2.5V VOUT < 2.5V CONDITIONS MIN 2.5 2.0 -1 -1.5 -2 -3 1.25 TA = +85C TA = 0C to +85C 1.229 1.219 500 0.55 50 ISET IQ VIN VOUT VLNR VLDR VSET = 1.25V IOUT = 1mA IOUT = 500mA IOUT = 500mA VIN from (VOUT + 100mV) to 5.5V, ILOAD = 5mA IOUT = 1mA to 500mA 10Hz to 1MHz, COUT = 3.3F (ESR < 0.1) IOFF VIH VIL SHDN = GND, VIN = 5.5V 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V SHDN = IN or GND 1.6 0.6 10 100 -0.15 -100 135 175 120 0 0.4 115 0.1 15 175 +0.15 1.0 1.2 2.0 100 150 +100 250 2.2 1.250 2.15 TYP MAX 5.5 2.3 +1 +1.5 +2 +3 5 1.271 V 1.281 mARMS A A mV nA A mV %/V % VRMS A V nA % UNITS V V %
IOUT = 100mA, TA = 0C to +85C IOUT = 1mA to 500mA, VIN > VOUT + 0.5V, TA = 0C to +85C
Adjustable Output Voltage Range SET Voltage Threshold (Adjustable Mode) Maximum Output Current Short-Circuit Current Limit In-Regulation Current Limit SET Dual ModeTM Threshold SET Input Bias Current Ground-Pin Current Dropout Voltage (Note 1) Line Regulation Load Regulation Output Voltage Noise SHUTDOWN Shutdown Supply Current SHDN Input Threshold SHDN Input Bias Current VSET IOUT ILIM
VSET = 1.25V VIN = +2.7V, VOUT set to 2.0V, IOUT = 100mA VIN 2.7V VOUT = 0, VIN 2.7V VOUT > 96% of nominal value, VIN 2.7V
V
Dual Mode is a trademark of Maxim Integrated Products. 2 _______________________________________________________________________________________
500mA, Low-Dropout, Ripple-Rejecting LDO in MAX
ELECTRICAL CHARACTERISTICS (continued)
((VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER RESET OUTPUT Reset Output Low Voltage Operating Voltage Range for Valid Reset RST Output High Leakage Current RST Threshold RST Release Delay THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis TSHDN TSHDN 170 20 C C tRP VOL RST sinking 1mA RST sinking 100A V RST = +5.5V Rising edge, referred to VOUT(NOMINAL) Rising edge of OUT to rising edge of RST 83 1.4 86 4.5 1.0 0.01 0.1 5.5 100 89 8 V V nA % ms SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1857
ELECTRICAL CHARACTERISTICS
(VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Input Voltage Input Undervoltage Lockout Output Voltage Accuracy (Preset Mode) Adjustable Output Voltage Range SET Voltage Threshold (Adjustable Mode) Maximum Output Current Short-Circuit Current Limit SET Dual Mode Threshold SET Input Bias Current Ground-Pin Current Dropout Voltage (Note 1) Line Regulation Load Regulation SHUTDOWN Shutdown Supply Current SHDN Input Threshold SHDN Input Bias Current IOFF VIH VIL SHDN = GND, VIN = +5.5V 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V SHDN = IN or GND 1.6 0.6 100 15 A V nA ISET IQ VIN VOUT VLNR VLDR VSET = 1.25V IOUT = 1mA IOUT = 500mA VIN from (VOUT + 100mV) to 5.5V, ILOAD = 5mA IOUT = 1mA to 500mA -0.15 VSET IOUT ILIM VOUT = 0 SYMBOL VIN VUVLO VOUT Rising or falling IOUT = 1mA to 500mA VSET = 1.25V IOUT = 100mA CONDITIONS MIN 2.5 2.0 -3 1.25 1.212 500 0.55 50 -100 2.2 150 +100 250 175 +0.15 1.0 MAX 5.5 2.3 +3 5 1.288 UNITS V V % V V mARMS A mV nA A mV %/V %
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER RESET OUTPUT Reset Output Low Voltage Operating Voltage Range for Valid Reset RST Output High Leakage Current RST Threshold RST Release Delay tRP VOL RST sinking 1mA RST sinking 100A V RST = +5.5V Rising edge, referred to VOUT(NOMINAL) Rising edge of OUT to rising edge of RST 83 1.4 1.0 0.1 5.5 100 89 8 V V nA % ms SYMBOL CONDITIONS MIN MAX UNITS
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 -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, CIN = 1F, COUT = 3.3F, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX1857 toc01
OUTPUT VOLTAGE vs. TEMPERATURE
IOUT = 0mA
MAX1857 toc02
DROPOUT VOLTAGE vs. OUTPUT CURRENT
TA = +85C 250 DROPOUT VOLTAGE (mV) TA = +25C 200 150 100 50 0 TA = -40C
MAX1857 toc03
4.80
4.80
300
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V) 1000
4.76
4.78
VIN = 5.25V
4.76
4.72 VIN = 5.00V 4.68
4.74
4.72
4.64 0 200 400 600 800 OUTPUT CURRENT (mA)
4.70 -55 -25 5 35 65 95 125 TEMPERATURE (C)
0
200
400
600
800
1000
OUTPUT CURRENT (mA)
4
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
Typical Operating Characteristics (continued)
(VIN = +5.25V, VOUT = 4.75V, SHDN = IN, SET = GND, CIN = 1F, COUT = 3.3F, TA = +25C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
70 60 PSRR (dB) 50 40 30 20 10 0 0.01 0.1 1 10 100 1000 FREQUENCY (kHz) 10s/div A: VOUT = 4.75V, 50mV/div B: IOUT = 5mA TO 500mA, 200mA/div VIN = 5.25V, CIN = 10F COUT = 3.3F IOUT = 50mA
MAX1857 toc04
LOAD-TRANSIENT RESPONSE
MAX1857 toc05
80
4.80V 4.75V 4.70V 600mA 400mA B 200mA 0 A
LOAD-TRANSIENT RESPONSE NEAR DROPOUT
MAX1857 toc06
SWITCHING POWER-SUPPLY RIPPLE REJECTION
MAX1857 toc07
4.80V 4.75V 4.70V 4.65V 400mA 200mA 0 10s/div A: VOUT = 4.75V, 50mV/div B: IOUT = 5mA TO 500mA, 200mA/div VIN = VOUT + 100mV = 4.85V, CIN = 10F 2s/div A: MAX1632: VIN = 9V, VOUT = 5.0V, 20mV/div B: MAX1857: VOUT = 4.75V, IOUT = 500mA, 2mV/div OUTMAX1632 = INMAX1857 B 4.75V B A 5.0V A
SHUTDOWN WAVEFORM
MAX1857 toc08
RST WAVEFORM
MAX1857 toc09
2V 1V 0 6V 4V 2V 0 40s/div A: VSHDN = 0 TO 2V, 1V/div B: VOUT = 4.75V, 2V/div ROUT = 9.5 (500mA) B 0 0 A 0
A
B
C
20ms/div A: VIN = 0 TO 5.5V, 2V/div B: VOUT = 4.75V, ROUT = 95, 2V/div C: VRST, 100k TO OUT, 2V/div
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
Pin Description
PIN 1, 2 NAME IN FUNCTION Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with a 1F capacitor or greater to GND (see Capacitor Selection and Regulator Stability). Connect both input pins together externally. 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 100k pullup resistor to OUT. Active-Low Shutdown Input. A logic low reduces supply current to 0.1A. In shutdown, the RST output is low and OUT is pulled low through an internal 5k resistor. Connect to IN for normal operation. Ground 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. Regulator Output. Sources up to 500mA. Bypass with a 3.3F low-ESR capacitor to GND. Use a 4.7F capacitor for output voltages below 2V. Connect both output pins together.
3
RST
4 5 6 7, 8
SHDN GND SET OUT
VIN = +2.5V TO +5.5V CIN 1F
IN IN
THERMAL SENSOR MOSFET DRIVER WITH I LIM OUT VOUT = 1.25V TO 5.0V COUT 3.3F
ON OFF
SHDN OUT SHUTDOWN LOGIC ERROR AMPLIFIER VREF 1.25V 5k
LOGIC SUPPLY VOLTAGE (VOUT) RRST 100k TO C RST
R1
MAX1857
SET DELAY TIMER R2 86% VREF 100mV GND
Figure 1. Functional Diagram 6 _______________________________________________________________________________________
500mA, Low-Dropout, Ripple-Rejecting LDO in MAX 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.
R1 = R2 IN V IN = +2.5V TO +5.5V IN OUT OUT VOUT VOUT 1.25V -1
CIN 1F ON SHDN OFF
MAX1857
COUT 3.3F
R1
SET
R2 RST GND
Figure 2. Adjustable Output Using External Feedback Resistors
in the 25k to 100k 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.
Internal P-Channel Pass Transistor
The MAX1857 features a 0.25 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 175A of quiescent current under heavy loads as well as in dropout.
Shutdown
Pull SHDN low to enter shutdown. During shutdown, the output is disconnected from the input and supply current drops to 0.1A. When in shutdown, RST pulls low and OUT is discharged through an internal 5k 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.
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
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 100k resistor works well for most applications. RST can be used as a power-on-reset (POR) signal to a microcontroller (C), or drive an external LED to indicate power failure. When the MAX1857 is
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
shut down, RST is held low independent of the output voltage. If unused, leave RST grounded or unconnected.
0.7 MAX PACKAGE OPERATING REGION AT TJ(MAX) = +150C 0.6 CONTINUOUS CURRENT LIMIT 0.5 TA = +50C 0.4 TYPICAL VDROPOUT LIMIT
Current Limit
MAXIMUM OUTPUT CURRENT (A)
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.
TA = +70C
0.3
MAXIMUM SUPPLY VOLTAGE LIMIT (VOUT = 1.25V)
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the MAX1857. When the junction temperature exceeds TJ = +170C, 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 20C, 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 = +150C.
0.2
0.1
TA = +85C
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
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) / ( JC + CA) where TJ - TA is the temperature difference between the MAX1857 die junction and the surrounding air; JC is the thermal resistance from the junction to the case; and 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.
equivalent series resistance (ESR) capacitor between OUT and ground. For output voltages less than 2V, use a 4.7F 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 10F. The output capacitor's (COUT) ESR affects stability and output noise. Use output capacitors with an ESR of 0.1 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 10F. 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-
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 1F capacitor between IN and ground and a 3.3F low
8
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX 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.
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 150A in dropout.
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500mA, Low-Dropout, Ripple-Rejecting LDO in MAX MAX1857
Package Information
8LUMAXD.EPS
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 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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