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19-1860; Rev 1; 3/01
500mA Low-Dropout Linear Regulator in SOT23
General Description
The MAX1818 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 voltage (see Selector Guide) or can be adjusted from 1.25V to 5.0V with an external resistive divider. An internal PMOS pass transistor allows the low 125A 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 that indicates when the output is out of regulation, a 0.1A shutdown, short-circuit protection, and thermal shutdown protection. The device is available in a miniature 800mW 6-pin SOT23 package. o Guaranteed 500mA Output Current o Low 120mV Dropout at 500mA o 1% Output Voltage Accuracy Preset at 1.5V, 1.8V, 2.0V, 2.5V, 3.3V, 5V Adjustable from 1.25V to 5.0V o Power OK Output o Low 125A Ground Current o 0.1A Shutdown Current o Thermal Overload Protection o Output Current Limit o Tiny 800mW 6-Pin SOT23 Package
Features
MAX1818
Ordering Information
PART* MAX1818EUAT_ _ TEMP RANGE -40C to +85C PIN-PACKAGE 6 SOT23-6
Applications
Notebook Computers Cellular and Cordless Telephones Personal Digital Assistants (PDAs) Palmtop Computers Base Stations USB Hubs Docking Stations
*Insert the desired two-digit suffix (see Selector Guide) into the blanks to complete the part number. Note: The MAX1818 requires a special solder temperature profile described in the Absolute Maximum Ratings section.
Selector Guide
PART AND SUFFIX MAX1818EUT15 MAX1818EUT18 MAX1818EUT20 MAX1818EUT25 MAX1818EUT33 MAX1818EUT50 VOUT 1.5V or Adj 1.8V or Adj 2.0V or Adj 2.5V or Adj 3.3V or Adj 5.0V or Adj SOT23 TOP MARK AASO AANU AANV AANF AANG AANH
Pin Configuration
TOP VIEW
IN 1 6 OUT VIN = 2.5V TO 5.5V
Typical Operating Circuit
IN NC CIN 1F OUT VOUT COUT 3.3F
POK 2
MAX1818
MAX1818
5 SET ON SHDN OFF POK
RPOK 100k TO C
SHDN 3
4
GND
SOT23
SET
GND
________________________________________________________________ Maxim Integrated Products
1
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500mA Low-Dropout Linear Regulator in SOT23 MAX1818
ABSOLUTE MAXIMUM RATINGS
IN, SHDN, POK, SET to GND ...................................-0.3V to +6V OUT to GND ................................................-0.3V to (VIN + 0.3V) Output Short-Circuit Duration ...............................................1min Continuous Power Dissipation (TA = +70C) (Note 1) 6-Pin SOT23 (derate 10mW/C above +70C)..............800mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) (Note 2) ...................+300C
Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air. With minimal copper, the SOT23 package dissipates 712mW at +70C. With a quarter square inch of copper, it will dissipate 790mW at +70C. Copper should be equally shared between the IN, OUT, and GND pins. Note 2: This device is constructed using a unique set of packaging techniques that imposes a limit on the thermal profile to which the device can be exposed during board-level solder attach and rework. The limit permits only the use of the solder profiles recommended in the industry standard specification, IPC JEDEC-J-STD-020A, paragraph 7.6, Table 3 for the IR/VPR and convection reflow. Preheating is required. Hand or wave soldering is not allowed.
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 + 500mV or VIN = +2.5V, whichever is greater; SHDN = IN, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 3)
PARAMETER Input Voltage Input Undervoltage Lock-Out SYMBOL VIN VUVLO Rising, 75mV hysteresis IOUT = 100mA, TA = +25C, VOUT 2.0V Output Voltage Accuracy (Preset Mode) IOUT = 100mA, VOUT < 2.0V VOUT IOUT = 100mA, TA = -40C to +85C IOUT = 1mA to 500mA, VIN > VOUT + 0.5V, TA = -40C to +85C Adjustable Output Voltage Range SET Voltage Threshold (Adjustable Mode) Guaranteed Output Current (RMS) Short-Circuit Current Limit In-Regulation Current Limit SET Dual ModeTM Threshold SET Input Bias Current Ground-Pin Current ISET IQ VSET = 1.25V IOUT = 100A IOUT = 500mA VOUT = 5V Dropout Voltage (Note 4) VIN - VOUT IOUT = 500mA VOUT = 3.3V VOUT = 2.5V Line Regulation VLNR VIN from (VOUT + 100mV) to 5.5V, ILOAD = 5mA -0.15 VSET VIN = 2.7V, IOUT = 100mA, VOUT set to 2.0V VIN 2.7V VOUT = 0, VIN 2.7V VOUT > 96% of nominal value, VIN 2.7V 50 -100 125 140 100 120 210 0 220 215 360 +0.15 %/V mV TA = 0C to +85C TA = -40C to +85C CONDITIONS MIN 2.5 2.0 -1 -1.5 -2.5 -3 1.25 1.225 1.213 500 0.55 0.8 1.6 100 150 +100 250 1.8 1.250 2.15 TYP MAX 5.5 2.3 +1 +1.5 +2.5 +3 5 1.275 V 1.288 mA A A mV nA A V % UNITS V V
IOUT ILIM
Dual Mode is a trademark of Maxim Integrated Products 2 _______________________________________________________________________________________
500mA Low-Dropout Linear Regulator in SOT23
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VOUT + 500mV or VIN = +2.5V, whichever is greater; SHDN = IN, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 3)
PARAMETER Load Regulation Output Voltage Noise SHUTDOWN Shutdown Supply Current SHDN Input Threshold SHDN Input Bias Current POK OUTPUT POK Output Low Voltage Operating Voltage Range for Valid POK POK Output High Leakage Current POK Threshold THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis TSHDN TSHDN 170 20 C C VOL POK sinking 1mA POK sinking 100A POK = 5.5V, TA = +25C TA = +85C Rising edge, referred to VOUT(NOMINAL) 90 1.0 1 5 93 96 0.01 0.1 5.5 25 V V nA % IOFF VIH VIL I SHDN SHDN = GND, VIN = 5.5V 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V SHDN = IN or GND, TA = +25C TA = +85C 1 5 1.6 0.6 25 0.1 15 A V nA SYMBOL VLDR CONDITIONS IOUT = 1mA to 500mA 10Hz to 1MHz, COUT = 3.3F (ESR < 0.1) MIN TYP 0.4 115 MAX 1.0 UNITS % VRMS
MAX1818
Note 3: All devices are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design. Note 4: The Dropout Voltage is defined as VIN - VOUT, when VOUT is 100mV below the value of VOUT measured for VIN = VOUT(NOM) + 500mV. 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) +7004mV. For VOUT(NOM) > 3.5V, Typical Dropout = 120mV; Maximum Dropout = 220mV.
Typical Operating Characteristics
(VIN = (VOUT + 500mV) or +2.5V, whichever is greater; SHDN = IN, CIN = 1F, COUT = 3.3F, TA = +25C, unless otherwise noted.)
GROUND PIN CURRENT vs. INPUT VOLTAGE
MAX1818 toc01
GROUND PIN CURRENT vs. LOAD CURRENT
MAX1818 toc02
GROUND PIN CURRENT vs. TEMPERATURE
ILOAD = 150mA GROUND PIN CURRENT (A) 160 150 140 1.5V OUTPUT 130 120 110 5.0V OUTPUT
MAX1818 toc03
250 225 GROUND PIN CURRENT (A) 200 175 150 125 100 75 50 25 0 1.8V OUTPUT 3.3V OUTPUT ILOAD = 150mA
160 145 GROUND PIN CURRENT (A) 130 115 100 85 70 55 40 1.8V OUTPUT 2.5V OUTPUT 3.3V OUTPUT
170
2.5V OUTPUT
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A)
-40
-15
10
35
60
85
TEMPERATURE (C)
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500mA Low-Dropout Linear Regulator in SOT23 MAX1818
Typical Operating Characteristics (continued)
(VIN = (VOUT + 500mV) or +2.5V, whichever is greater; SHDN = IN, CIN = 1F, COUT = 3.3F, TA = +25C, unless otherwise noted.)
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX1818 toc04
OUTPUT VOLTAGE ACCURACY vs. LOAD CURRENT
3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 0 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -40
MAX1818 toc05
OUTPUT VOLTAGE ACCURACY vs. TEMPERATURE
VOUT = 1.5V TO 5.0V ILOAD = 150mA
MAX1818 toc06
180 VOUT = 3.3V 150 DROPOUT VOLTAGE (mV) 120 90 60 TA = -40C 30 0 0 0.1 0.2 0.3 0.4 TA = +85C
OUTPUT VOLTAGE ACCURACY (%)
3.3V OUTPUT 2.5V OUTPUT
TA = +25C
1.8V OUTPUT
0.5
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A)
OUTPUT VOLTAGE ACCURACY (%)
-15
10
35
60
85
LOAD CURRENT (A)
TEMPERATURE (C)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX1818 toc07
LINE TRANSIENT
MAX1818 toc08
LOAD-TRANSIENT RESPONSE
MAX1818 toc09
80 70 60 PSRR (dB) 50 40 COUT = 3.3F VOUT = 3.3V RLOAD = 100
VOUT
2.5V 10mV/div
VIN = 3.3V VOUT = 2.5V IOUT 500mA 100mA
3.5V 500mV/div
30 20 10 0 0.01 0.1 1 10 100 1000 100s/div VIN
VOUT
40s/div
FREQUENCY (kHz)
LOAD-TRANSIENT RESPONSE NEAR DROPOUT
MAX1818 toc10
POWER-ON RESET
MAX1818 toc11
VOUT 100mV/div
VIN = VOUT + 100mV VOUT = 3.3V
VPOK
0 VOUT 2V/div
200mA IOUT
VIN
0
0 0
10s/div
10ms/div
4
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20mV/div
500mA Low-Dropout Linear Regulator in SOT23
Typical Operating Characteristics (continued)
(VIN = (VOUT + 500mV) or +2.5V, whichever is greater; SHDN = IN, CIN = 1F, COUT = 3.3F, TA = +25C, unless otherwise noted.)
SHUTDOWN WAVEFORM
MAX1818 toc12
MAX1818
SHORT-CIRCUIT CURRENT LIMIT vs. SUPPLY VOLTAGE
SHORT-CIRCUIT CURRENT LIMIT (A) 1.10 1.09 1.08 1.07 1.06 1.05 1.04 1.03 1.02 1.01 1.00 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VOUT(NOM) = +2V
MAX1818 toc13
1.11
SHUTDOWN VOLTAGE
0
VOUT
0 2V/div
POK
0
200s/div
SUPPLY VOLTAGE (V)
Pin Description
PIN 1 2 3 4 5 6 NAME IN POK SHDN GND SET OUT FUNCTION Regulator Input. Supply voltage can range from 2.5V to 5.5V. Bypass with a 1F capacitor to GND (see Capacitor Selection and Regulator Stability). Open-Drain POK Output. POK remains low while the output voltage (VOUT) is below the POK threshold. Connect a 100k pull-up resistor from POK to OUT to obtain an output voltage. Active-Low Shutdown Input. A logic low reduces supply current below 15A. In shutdown, the POK output is low, and OUT is high impedance. Connect to IN for normal operation. Ground Voltage-Setting Input. Connect to GND for preset output. Connect to a resistive voltage-divider between OUT and GND 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.
Detailed Description
The MAX1818 is a low-dropout, low-quiescent-current linear regulator designed primarily for battery-powered applications. The device supplies loads up to 500mA and is available with preset output voltages. As illustrated in Figure 1, the MAX1818 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 which compares this reference with the age and amplifies the difference. If the age is lower than the reference error amplifier, feedback voltfeedback voltvoltage, 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.
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500mA Low-Dropout Linear Regulator in SOT23 MAX1818
VIN = 2.5V TO 5.5V CIN 1F MOSFET DRIVER WITH I LIM OUT ON OFF SHDN SHUTDOWN LOGIC ERROR AMPLIFIER 5k VOUT = 1.25V TO 5.0V COUT 3.3F VREF 1.25V IN
THERMAL SENSOR
LOGIC SUPPLY VOLTAGE (VOUT) RPOK 100k TO C POK
R1
MAX1818
SET
R2 93% VREF 100mV GND
Figure 1. Functional Diagram
Additional blocks include an output current limiter, thermal sensor, and shutdown logic.
Internal P-Channel Pass Transistor
The MAX1818 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 MAX1818 does not suffer from these problems and consumes only 125A of quiescent current under heavy loads as well as in dropout.
put voltage (see Selector Guide). For example, the MAX1818EUT33 has a preset 3.3V output voltage. The output voltage may also be adjusted by connecting a voltage-divider from OUT to SET to GND (Figure 2). Select R2 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.
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, POK pulls low and OUT is high impedance. The capacitance and load at OUT determine the rate at which V OUT decays. SHDN can be pulled as high as 6V, regardless of the input and output voltage.
Output Voltage Selection
The MAX1818'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 out-
6
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500mA Low-Dropout Linear Regulator in SOT23 MAX1818
R1 = R2 V IN = 2.5V TO 5.5V IN OUT MAXIMUM OUTPUT CURRENT (mA) -1 1.25V VOUT VOUT
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE (POWER DISSIPATION LIMIT)
MAXIMUM RECOMMENDED OUTPUT CURRENT TA = +85C TA = +70C
MAX1818 fig03
600
CIN 1F ON SHDN OFF
MAX1818
COUT 3.3F
R1
400 MAXIMUM INPUT VOLTAGE 5.5 6.0
SET
200
VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V
R2 POK GND 0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V)
Figure 2. Adjustable Output Using External Feedback Resistors
Figure 3. Power Operating Regions: Maximum Output vs. Supply Voltage
POK Output
The power OK (POK) output pulls low when OUT is less than 93% of the nominal regulation voltage. Once OUT exceeds 93% of the nominal voltage, POK goes high impedance. POK is an open-drain N-channel output. To obtain a voltage output, connect a pullup resistor from POK to OUT. A 100k resistor works well for most applications. POK can be used as a power-okay (POK) signal to a microcontroller (C), or drive an external LED to indicate power failure. When the MAX1818 is shut down, POK is held low independent of the output voltage. If unused, leave POK grounded or unconnected.
the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction-temperature rating of TJ = +150C.
Operating Region and Power Dissipation
The MAX1818'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 V OUT ). The maximum allowed power dissipation is 800mW at TA = +70C or: PMAX = (TJ(MAX) - TA) / ( JC + CA) where TJ - TA is the temperature difference between the MAX1818 die junction and the surrounding air, JC is the thermal resistance of 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. For best heatsinking, the copper area should be equally shared between the IN, OUT, and GND pins. The MAX1818 delivers up to 0.5A RMS and operates with input voltages up to +5.5V, but not simultaneously. High output currents can only be sustained when inputoutput differential voltages are low, as shown in Figure 3.
Current Limit
The MAX1818 monitors and controls the pass transistor's gate voltage, limiting the output current to 0.8A (typ). This current limit doubles when the output voltage is within 4% of the nominal value to improve performance with large load transients.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the MAX1818. 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 again after the junction temperature cools by 20C, resulting in a pulsed output during continuous thermal overload conditions. Thermal overload protection protects the MAX1818 in
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7
500mA Low-Dropout Linear Regulator in SOT23 MAX1818
Applications Information
Capacitor Selection and Regulator Stability
Capacitors are required at the MAX1818'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 lowESR 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 powersupply rejection by using larger output capacitors, such as 10F. The output capacitor's (COUT) equivalent series resistance (ESR) affects stability and output noise. Use output capacitors with an ESR of 0.1 or less to ensure stability and optimum transient response. Surfacemount ceramic capacitors have very low ESR and are commonly available in values up to 10F. Connect CIN and COUT as close to the MAX1818 as possible to minimize the impact of PC board trace inductance. the input and output bypass capacitors and through passive filtering techniques. The MAX1818 load-transient response (see Typical Operating Characteristics) shows two components 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 100mA to 500mA is 8mV. Increasing the output capacitor's value and decreasing the ESR attenuates the overshoot.
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 MAX1818 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 MAX1818 ground current remains below 150A in dropout.
Noise, PSRR, and Transient Response
The MAX1818 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) versus frequency. When operating from noisy sources, improved supply-noise rejection and transient response can be achieved by increasing the values of
Chip Information
TRANSISTOR COUNT: 845
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500mA Low-Dropout Linear Regulator in SOT23
Package Information
6LSOT.EPS
MAX1818
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ______________________9 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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