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19-1654; Rev 0; 4/00
Low-Dropout, Low IQ, 1A Linear Regulator
General Description
The MAX1793 low-dropout linear regulator (LDO) operates from +2.5V to +5.5V and delivers a guaranteed 1A load current with a low 210mV dropout. The high-accuracy (1%) output voltage is preset at 3.3V or 2.5V or can be adjusted with an external resistor-divider. An internal PMOS pass transistor allows a low 125A supply current, making the MAX1793 ideal for batteryoperated portable equipment. Other features include a built-in reset output, low-power shutdown, and short-circuit and thermal overload protection. The MAX1793 is available in a 1.7W, 16-pin power TSSOP package, which is 30% smaller than a SOT223 package and only 1.1mm high. o Guaranteed 1A Output Current o Low 210mV Dropout at 1A o 1% Output Voltage Accuracy Preset at 3.3V or 2.5V Adjustable from 1.25V to 5.0V o Reset Output (4ms delay) o Low 125A Ground Current o 0.1A Shutdown o Low 115VRMS Output Noise o Thermal Overload Protection o Output Current Limit o Tiny TSSOP Power Package (1.7W) 30% Smaller than SOT223 (only 1.1mm high)
Features
MAX1793
________________________Applications
Notebook Computers Cordless Telephones Cellular Phones Modems Hand-Held Instruments PDAs and Palmtop Computers
PART TEMP. RANGE PINPACKAGE VOUT (V)
Ordering Information
MAX1793EUE-33 -40C to +85C 16 TSSOP-EP* 3.3 or Adj MAX1793EUE-25 -40C to +85C 16 TSSOP-EP *EP = Exposed Pad 2.5 or Adj
Typical Operating Circuit
TOP VIEW
IN NC IN CIN IN IN IN ON OFF SET GND SHDN OUT N.C. 1 OUT COUT IN 2 IN 3 IN 4 IN 5 RST RESET OUTPUT RST 6 SHDN 7 N.C. 8
Pin Configuration
16 N.C. 15 OUT 14 OUT
MAX1793
OUT OUT OUT
MAX1793
13 OUT 12 OUT 11 SET 10 GND 9 N.C.
TSSOP-EP
________________________________________________________________ Maxim Integrated Products 1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
ABSOLUTE MAXIMUM RATINGS
IN, SHDN, RST to GND ............................................-0.3V to +6V OUT, SET to GND ........................................-0.3V to (VIN + 0.3V) Output Short-Circuit Duration ............................................Infinite Continuous Power Dissipation (TA = +70C) 16-Pin TSSOP (derate 21.3mW/C above +70C) ..........1.7W 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 = VOUT + 0.5V, SHDN = IN, TA = +0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Input Voltage Input Undervoltage Lockout Output Voltage Accuracy (preset mode, SET = GND) SYMBOL VIN VIN TA = +85C, IOUT = 250mA TA = 0C to +85C, IOUT = 250mA TA = 0C to +85C, IOUT = 1mA to 1A, VIN > VOUT + 0.5V TA = +85C, IOUT = 250mA, VIN = 3V SET Voltage Threshold (for adjustable output) Adjustable Output Voltage Range Maximum Output Current Short-Circuit Current Limit In-Regulation Current Limit SET Pin Dual Mode Threshold SET Input Bias Current Ground Current Dropout Voltage (Note 1) Line Regulation Load Regulation Output Voltage Noise Shutdown Supply Current Output Pulldown Resistance in Shutdown SHDN Input Threshold SHDN Input Bias Current RST Output Low Voltage VIH VIL I SHDN VOL IOFF ISET IGND VIN - VOUT VLNR VLDR VSET = +1.25V IOUT = 100A IOUT = 1A, SET = GND MAX1793-33 MAX1793-25 -0.15 125 210 290 0 0.7 115 0.1 5 1.6 0.01 0.6 1 0.1 16 IOUT ILIM Continuous, VIN = 3V VOUT = 0, VIN = 3V VOUT within 4% of nominal output voltage, VIN = 5.5V 50 TA = 0C to +85C, IOUT = 250mA, VIN = 3V TA = 0C to +85C, IOUT = 1mA to 1A, VIN = 3V CONDITIONS MIN 2.5 2.0 -1 -2 -3 1.229 1.219 1.212 1.25 1 1.1 1.8 2.8 3.3 5.5 150 100 200 350 450 0.15 1.250 TYP MAX 5.5 2.3 1 2 3 1.271 1.281 1.288 5 V A A A mV nA A mV %/V % VRMS A k V A V V % UNITS V V
VIN from (VOUT + 0.1V) to +5.5V, IOUT = 5mA, SET = GND IOUT = 100A to 1A 10Hz to 1MHz, COUT = 6.8F (ESR < 0.1) SHDN = GND, VIN = +5.5V SHDN = GND +2.5V < VIN < +5.5V SHDN = GND or IN ISINK = 1mA
2
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Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VOUT + 0.5V, SHDN = IN, TA = +0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Operating Voltage Range for RST Valid RST Output High Leakage RST Trip Level Referred to Nominal VOUT RST Release Delay Thermal Shutdown Temperature T SHDN SYMBOL ISINK = 100A V RST = +5.5V Rising edge Rising edge Typical thermal hysteresis = 20C 90 2 CONDITIONS MIN 1.0 0.01 94 4 170 TYP MAX 5.5 1 96 6 UNITS V A % VOUT ms C
ELECTRICAL CHARACTERISTICS
(VIN = VOUT + 0.5V, SHDN = IN, TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Input Voltage Input Undervoltage Lockout Output Voltage Accuracy (preset mode, SET = GND) SET Voltage Threshold (for adjustable output) Adjustable Output Voltage Range Maximum Output Current Short-Circuit Current Limit In-Regulation Current Limit SET Pin Dual Mode Threshold SET Input Bias Current Ground Current Dropout Voltage (Note 1) Line Regulation Shutdown Supply Current SHDN Input Threshold SHDN Input Bias Current RST Output Low Voltage ISET IGND VIN VOUT VLNR IOFF VIH VIL ISH D N VOL VSET = +1.25V IOUT = 100A IOUT = 1A, SET = GND MAX1793-33 MAX1793-25 -0.15 IOUT ILIM Continuous, VIN 3V VOUT = 0, VIN 3V VOUT within 4% of nominal output voltage, VIN = 5.5V 50 SYMBOL VIN VIN IOUT = 250mA IOUT = 1mA to 1A, VIN > VOUT + 0.5V IOUT = 250mA, VIN = 3V IOUT = 1mA to 1A, VIN = 3V CONDITIONS MIN 2.5 2.0 -2.5 -3.2 1.216 1.210 1.25 1 1.1 TYP MAX 5.5 2.3 2.5 3.2 1.284 1.290 5 UNITS V V % V V A A A mV nA A mV %/V A V A V
3.3 5.5 150 100 200 350 450 0.15 16
VIN from (VOUT + 0.1V) to +5.5V, IOUT = 5mA, SET = GND SHDN = GND, VIN = +5.5V +2.5V < VIN < +5.5V SHDN = GND or IN ISINK = 1mA
1.6 0.6 1 0.1
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Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VOUT + 0.5V, SHDN = IN, TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Operating Voltage Range for RST Valid RST Output High Leakage RST Trip Level Referred to Nominal VOUT RST Release Delay SYMBOL ISINK = 10A V RST = +5.5V Rising edge Rising edge 90 2 CONDITIONS MIN 1.0 TYP MAX 5.5 1 96 6 UNITS V A % VOUT ms
Note 1: Dropout voltage is defined as VIN - VOUT, when VOUT is 100mV below the value of VOUT for VIN = VOUT + 0.5V. Note 2: Specifications to -40C are guaranteed by design and not production tested.
Typical Operating Characteristics
(Circuit of Figure 2, VIN = +5V, V SHDN = VIN, VOUT = +3.3V, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1793 toc01
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1793 toc02
OUTPUT VOLTAGE vs. TEMPERATURE
3.315 3.310 OUTPUT VOLTAGE (V) 3.305 3.300 3.295 3.290 3.285 3.280 IOUT = 250mA
MAX1793 toc03
3.305 3.303 OUTPUT VOLTAGE (V) 3.301 3.299 3.297 3.295 3.293 1 10 100 1000 LOAD CURRENT (mA)
3.5 IOUT = 0 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 0 0 1 2 3 4 5 INPUT VOLTAGE (V) IOUT = 1A
3.320
3.275 3.270 -40 -20 0 20 40 60 80 TEMPERATURE (C)
GROUND CURRENT vs. INPUT VOLTAGE
MAX1793 toc04
GROUND CURRENT vs. LOAD CURRENT
MAX1793 toc05
GROUND CURRENT vs. TEMPERATURE
200 190 GROUND CURRENT (A) 180 170 160 150 140 130 120 110 IOUT = 0 IOUT = 250mA
MAX1793 toc06
250 IOUT = 1A 200 GROUND CURRENT (A)
250 225 200 GROUND CURRENT (A) 175 150 125 100 75 50 25
210
150 IOUT = 0
100
50
0 0 1 2 3 4 5 INPUT VOLTAGE (V)
0 1 10 100 1000 LOAD CURRENT (mA)
-40
-20
0
20
40
60
80
TEMPERATURE (C)
4
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Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = +5V, V SHDN = VIN, VOUT = +3.3V, TA = +25C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX1793 toc07
DROPOUT VOLTAGE vs. LOAD CURRENT
300 250 DROPOUT VOLTAGE (mV) 200 150 100 50 0 0 200 400 1000 1200 LOAD CURRENT (mA) 600 800 PSRR (dB) 60
OUTPUT NOISE SPECTRAL DENSITY vs. FREQUENCY
MAX1793 toc08 MAX1793 toc09
10
IOUT = 250mA 50 40 30 20 10 0 0.01 0.1 1 10 100
NOISE (V/Hz)
1
0.1 IOUT = 250mA
0.01 1000 0.01 0.1 1 10 100 1000 FREQUENCY (kHz) FREQUENCY (kHz)
OUTPUT NOISE vs. LOAD CURRENT
MAX1793 toc10
LINE-TRANSIENT RESPONSE
MAX1793 toc11
140 120 OUTPUT NOISE (VRMS) 100 80 60 40 20
5V VIN 3.4V
VOUT 10mV/div AC-COUPLED IOUT = 100mA
0 0.001 0.01 0.1 1 100s/div LOAD CURRENT (A)
LOAD-TRANSIENT RESPONSE
MAX1793 toc12
OUTPUT NOISE
MAX1793 toc13
1A IOUT 100mA 100V/div
VOUT
20mV/div AC-COUPLED
40s/div
4ms/div
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5
Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = +5V, V SHDN = VIN, VOUT = +3.3V, TA = +25C, unless otherwise noted.)
SHUTDOWN RESPONSE
MAX1793 toc14
RESET OUTPUT RESPONSE
MAX1793 toc15
VOUT 2V/div
VIN
5V/div
VOUT
2V/div
VSHDN 5V/div IOUT = 100mA 40s/div
RST
2V/div
1ms/div
Pin Description
PIN 1, 8, 9, 16 2, 3, 4, 5 NAME N.C. No Connection. Not internally connected. Regulator Input. Supply voltage ranges from +2.5V to +5.5V. Bypass with a 4.7F capacitor to GND (see Capacitor Selection and Regulator Stability). These inputs are internally connected, but they also must be externally connected for proper operation. Reset Output. Open-drain output is low when VOUT is 6% below its nominal value. 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 pull-up resistor to OUT to obtain an ouput voltage. Active-Low Shutdown Input. A logic low disables the output and reduces the supply current to 0.1A. In shutdown, the RST output is low and OUT is pulled low through an internal 5k resistance. Connect SHDN to IN for normal operation. Ground. This pin and the exposed pad also function as a heatsink. Solder both to a large pad or to the circuit-board ground plane to maximize power dissipation. Voltage-Setting Input. Connect to GND to select the factory-preset output voltage. Connect SET to an external resistor-divider for adjustable-output operation. Regulator Output. Bypass with a 6.8F low-ESR capacitor to GND. Connect all OUT pins together at the IC. FUNCTION
IN
6
RST
7
SHDN
10 11 12, 13, 14, 15
GND SET OUT
6
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Low-Dropout, Low IQ, 1A Linear Regulator
Detailed Description
The MAX1793 features Dual ModeTM operation, allowing a fixed output of +3.3V or +2.5V or an adjustable output from +1.25V to +5V. The regulators are guaranteed to supply 1A of output current. As Figure 1 shows, the device consists of a +1.25V reference, error amplifier, MOSFET driver, P-channel pass transistor, internal feedback voltage-divider, Dual Mode comparator, and 4ms reset output. The +1.25V reference is connected to the inverting input of the error amplifier. The error amplifier compares this reference with the selected feedback voltage and amplifies the difference. The MOSFET driver reads the error signal and applies the appropriate drive to the P-channel transistor. If the feedback voltage is lower than the reference, the pass transistor's gate is pulled lower, allowing more current to pass and increase the output voltage. If the feedback voltage is high, the pass transistor's gate is pulled up, allowing less current to pass to the output. The low VOUT comparator senses when the feedback voltage has dropped 6% below its expected level, causing RST to go low. The output voltage is fed back through either an internal resistor-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.
MAX1793
Dual Mode is a trademark of Maxim Integrated Products.
IN SHUTDOWN THERMAL SENSOR ERROR AMP MOSFET DRIVER WITH FOLDBACK CURRENT LIMIT
PMOS
SHDN
SHUTDOWN LOGIC OUT 94% VOUT DETECTOR IN RST NMOS 1.25V REFERENCE OUT 1175mV 4ms
4ms DELAY TIMER
SET R1
MAX1793
DUAL MODE COMPARATOR GND
100mV R2
Figure 1. Functional Diagram _______________________________________________________________________________________ 7
Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
Internal P-Channel Pass Transistor
The MAX1793 features a 1A 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 MAX1793 does not suffer from these problems and consumes only 225A of quiescent current under heavy loads, as well as in dropout.
Shutdown
A logic low on SHDN disables the MAX1793. In shutdown, the pass transistor, control circuitry, reference, and all internal circuits are turned off, reducing supply current to typically 0.1A. Connect SHDN to IN for normal operation. In shutdown, RST goes low and OUT is discharged to GND with a 5k internal resistance.
RST Comparator
The MAX1793 features a low VOUT indicator that asserts when the output voltage falls out of regulation. The open-drain RST output goes low when OUT falls 6% below its nominal output voltage. RST remains low for 4ms after OUT has returned to its nominal value. A 100k pull-up resistor from RST to a suitable logic supply voltage (typically OUT) provides a logic control signal. RST can be used as a power-on-reset (POR) signal to a microcontroller or can drive an external LED to indicate power failure. RST is low during shutdown.
Output Voltage Selection
The MAX1793 features Dual Mode operation. In preset voltage mode, the output of the MAX1793 is set to +3.3V or +2.5V (see Ordering Information). Select this mode by connecting SET to GND (Figure 2). In adjustable mode, an output is selected between +1.25V and +5V using two external resistors connected as a voltage divider to SET (Figure 3). The output voltage is determined by the following equation: VOUT = VSET [1 + (R1 / R2)] where VSET = +1.25V. To simplify resistor selection: R1 = R2 [(VOUT / VSET) - 1] Since the input bias current at SET is less than 100nA, large resistance values can be used for R1 and R2 to minimize power consumption without losing efficiency. Up to 125k is acceptable for R2. In preset voltage mode, the impedance from SET to GND should be less than 10k. Otherwise, spurious conditions could cause the voltage at SET to exceed the 50mV dual-mode threshold.
Current Limiting
The MAX1793 features a current limit that monitors the pass transistor, typically limiting short-circuit output current to 1.8A. The current limit is increased to approximately 2.8A when the output voltage is in regulation, improving performance with large transient loads. The output can be shorted to ground for an indefinite period of time without damaging the device.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the MAX1793. When the junction temperature exceeds TJ = +170C, a thermal sensor turns off the pass transistor, allowing the IC to cool. The thermal sensor turns the pass transistor on once the IC's junction
IN NC IN IN IN IN ON OFF SHDN
OUT
IN NC IN CIN = 4.7F IN IN IN ON OFF SHDN
MAX1793
OUT OUT OUT RST R1
OUT COUT = 6.8F
OUT
CIN = 4.7F
MAX1793
OUT OUT OUT RST SET GND
OUT COUT = 6.8F
RESET OUTPUT GND SET R2
RESET OUTPUT
Figure 2. Typical Operating Circuit with Preset Output Voltage
Figure 3. Typical Operating Circuit with Adjustable Output Voltage
8
_______________________________________________________________________________________
Low-Dropout, Low IQ, 1A Linear Regulator
temperature drops approximately 20C. Continuous short-circuit conditions will result in a pulsed output. Thermal overload protection is designed to safeguard the MAX1793 in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction-temperature rating of TJ = +150C.
MAX1793
MAXIMUM OUTPUT CURRENT vs. INPUT-OUTPUT DIFFERENTIAL VOLTAGE
1.2 MAXIMUM CONTINUOUS CURRENT MAXIMUM OUTPUT CURRENT (A) 1.0 0.8 0.6 0.4 0.2 TJ(MAX) = +150C 0 0 1 2 3 4 5 6 INPUT-OUTPUT DIFFERENTIAL VOLTAGE (V) IN DROPOUT TA = +25C
Maximum power dissipation of the MAX1793 depends on the thermal resistance of the case and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated by the device is: P = IOUT (VIN - VOUT). The resulting maximum power dissipation is: PMAX = [(TJ(MAX) - TA) / (JC + CA)] where (T J(MAX) - T A ) is the temperature difference between the maximum allowed die junction (+150C) and the surrounding air, JC (junction-to-case) is the thermal resistance of the package chosen, and CA is the thermal resistance from the case through the PC board, copper traces, and other materials to the surrounding air. Figure 4 shows allowable power dissipation for typical PC boards at +25C, +50C, and +70C ambient temperatures. The MAX1793 TSSOP-EP package features an exposed thermal pad on its underside. This pad lowers the thermal resistance of the package by providing a direct heat conduction path from the die to the PC board. Additionally, the ground pin (GND) also channels heat. Connect the exposed thermal pad and GND to circuit ground by using a large pad, or multiple vias to the ground plane.
TA = +50C TA = +70C
Figure 4. Power Operating Region: Maximum Output Current vs. Input-Output Differential Voltage
Connect CIN and COUT as close to the IC as possible to minimize the impact of PC board trace inductance.
Noise, PSRR, and Transient Response
MAX1793 output noise is typically 115VRMS during normal operation. This is suitably low for most applications. See the output noise plot in the Typical Operating Characteristics. The MAX1793 is designed to achieve low dropout voltage and low quiescent current 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) versus frequency. When operating from very noisy sources, supply noise rejection and transient response can be improved by increasing the values of the input and output capacitors and employing passive postfiltering.
Applications Information
Capacitor Selection and Regulator Stability
Capacitors are required at the input and output of the MAX1793. Connect a 4.7F capacitor between IN and ground (CIN) and a 6.8F capacitor between OUT and ground (COUT). CIN serves only to lower the source impedance of the input supply and may be smaller than 4.7F when the MAX1793 is powered from regulated power supplies or low-impedance batteries. The output capacitor's equivalent series resistance (ESR) affects stability and output noise. COUT ESR should be 0.5 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. Other low-ESR (< 0.5) capacitors, such as surface-mount tantalum or OS-CON, may also be used.
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. Since a P-channel MOSFET is used as the pass device, dropout voltage is the product of RDS(ON) and load current (see Electrical Characteristics and Dropout Voltage vs. Load Current in the Typical Operating Characteristics). The MAX1793 operating current typically remains below 225A in dropout.
Chip Information
TRANSISTOR COUNT: 845
9
_______________________________________________________________________________________
MAXIMUM SUPPLY VOLTAGE
Operating Region and Power Dissipation
Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
Package Information
TSSOP.EPS
Note: The MAX1793EUE has an exposed thermal pad on the bottom side of the package.
10
______________________________________________________________________________________
Low-Dropout, Low IQ, 1A Linear Regulator
NOTES
MAX1793
11
______________________________________________________________________________________
Low-Dropout, Low IQ, 1A Linear Regulator MAX1793
NOTES
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.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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