MAX1534 Datasheet, PDF (8/16 Pages) Maxim Integrated Products – High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers

High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Pin Description
PIN
NAME
FUNCTION
Shutdown Control Input. Drive SHDN above 1V to start up, and below 0.9V to shut down. LX is high
1
SHDN
impedance in shut down, and supply current reduces to 3.5µA. Connect SHDN to IN for automatic
startup. SHDN can be connected to IN through a resistive voltage-divider to implement a
programmable undervoltage lockout.
Open-Drain Power-OK (POK) Output. POK asserts low while any output voltage is below the reset
2
POK
threshold. Connect a 100kΩ pullup resistor to OUT_. POK is driven low in shut down. If not used,
leave this pin unconnected.
3
GND
Ground. Connect backside pad to GND.
4
ILIM
Peak LX Current Control Input. Connect to IN for 1000mA peak LX current. Connect to GND for
500mA peak LX current.
5, 8
LX
Inductor Connection. Connect LX to external inductor and diode as shown in Figure 1. Both LX pins
must be connected together on the PC board.
6, 7
IN
Buck Regulator Input Supply Voltage. Input voltage range is 4.5V to 24V. Both IN pins must be
connected together on the PC board.
9
OUT2
Regulated LDO2 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω
typical ESR) ceramic capacitor to GND.
10
LDOIN
Input Supply for both LDOs. Supply voltage can range from 2.5V to 5.5V. Bypass with 2.2µF capacitor
to GND (see Capacitor Selection and LDO Stability).
11
OUT1
Regulated LDO1 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω
typical ESR) ceramic capacitor to GND.
12
BP
LDO Reference Noise Bypass. Bypass with a low-leakage 0.01µF ceramic capacitor for reduced
noise at both outputs.
13
FB1
Feedback Input for LDO1. For a fixed 3.3V output, connect PRESET and FB1 to GND. For an
adjustable output, connect PRESET = IN and connect a resistive divider between OUT1 and GND.
14
FB2
Feedback Input for LDO2. For a fixed 1.8V output, connect PRESET and FB2 to GND. For an
adjustable output, connect PRESET = IN and connect a resistive divider between OUT2 and GND.
Preset Feedback Select Input. Connect to GND for the preset 5V buck output voltage, preset 3.3V
15
PRESET OUT1 output voltage, and preset 1.8V OUT2 output voltage. Connect PRESET to IN to select
adjustable feedback mode for all three regulators.
16
FB3
Buck Output Feedback Input. For a fixed 5.0V output, connect PRESET to GND and FB3 to OUT3. For
an adjustable output, connect PRESET to IN and connect a resistive divider between OUT3 and GND.
Detailed Description
The MAX1534 regulator provides efficient light-load
power conversion for notebook computers or hand-held
devices that require keep-alive power or standby
power. The main step-down buck regulator uses a
unique peak current-limited control scheme, providing
high efficiency at light loads over a wide load range.
Operation up to 100% duty cycle allows the lowest pos-
sible dropout voltage, increasing the usable supply
voltage range. Under no load, the MAX1534 consumes
only 1mW, and in shutdown mode, it draws only 3.5µA.
The internal 24V switching MOSFET, internal current
sensing, and a high-switching frequency minimize PC
board space and component costs.
The MAX1534 includes two low-noise, low-dropout,
low-quiescent-current linear regulators. The linear regu-
lators are available with preset output voltages of 3.3V
and 1.8V. Each linear regulator can supply loads up to
160mA.
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