MAX1552 Datasheet, PDF (7/12 Pages) Maxim Integrated Products – Complete Power IC for Low-Cost PDAs

Complete Power IC for
Low-Cost PDAs
Pin Description
PIN
NAME
FUNCTION
1
COR1 1.5V, 200mA LDO Output for CPU Core. COR1 turns off when V_IN < 3V.
2
IN Input Voltage to the Device. Bypass IN to GND with a 1µF capacitor.
3
SDIG ^{3.3V, 200mA LDO Output for Secure Digital Card Slot. SDIG has reverse-current protection so SDIG can be}
biased when no power is present at IN. SDIG output turns off when V_IN < 3V or when ENSD goes low.
4
ENSD SDIG Enable Input. Drive ENSD low to turn off the SDIG output. Drive ENSD high to turn on the SDIG output.
5
REF 1.25V Reference. Bypass REF with a 0.1µF capacitor to GND.
6
RS
Reset Output. RS is an active-low, open-drain output that goes low when V_IN falls below 3.0V. RS deasserts
when V_IN goes above 3.4V. Connect a 1MΩ pullup resistor from RS to MAIN.
7
LBO
Low-Battery Output. LBO is an active-low, open-drain output that goes low when V_IN falls below 3.6V. LBO
deasserts when V_IN goes above 3.8V. Connect a 1MΩ pullup resistor from LBO to MAIN.
8
GND Ground
9
LX LCD Boost Switch. Connect LX to a boost inductor and a rectifying Schottky diode. See Figure 1.
10
SW
LCD True Shutdown Switch Output. SW is the power source for the boost inductor. SW turns on when ENLCD
is high.
11
SWIN
LCD True Shutdown Switch Input. The SWIN-to-SW switch turns off when ENLCD goes low or when V_IN < 3V.
Connect SWIN to IN.
12
LFB ^{LCD Feedback Input. Connect LFB to a resistor-divider network between the LCD output and GND. The}
feedback threshold is 1.25V.
13
ENLCD
Enable Input for LCD (Boost Regulator). Drive ENLCD high to activate the LCD boost. Drive ENLCD low to
shut down the LCD output.
14
ENC2 Enable Input for Secondary Core LDO (COR2). Drive ENC2 high to turn on COR2. Drive low to turn off COR2.
15
COR2 1.8V, 30mA LDO Output for Secondary Core. COR2 output turns off when V_IN < 3V or when ENC2 goes low.
16
MAIN 3.3V, 300mA LDO Output for Main Supply. MAIN output turns off when V_IN < 3V.
Detailed Description
Linear Regulators
The MAX1552 contains all power blocks and voltage
monitors for a small PDA. Power for logic and other
subsystems is provided by four LDOs:
• MAIN—Provides 3.3V at a guaranteed 350mA with
a typical current limit of 650mA.
• SDIG—Provides 3.3V at a guaranteed 250mA for
secure digital cards with a typical current limit at
310mA.
• COR1—1.5V for CPU core guarantees 250mA and
typically current limits at 450mA.
• COR2—1.8V for CODEC core guarantees 30mA
and typically current limits at 50mA.
MAIN and COR1 regulators are always on as long as
the IC is not in low-voltage shutdown (V_IN < 3V). COR2
and SDIG can be turned on and off independently
through logic signals at ENC2 and ENSD, respectively.
When SDIG is turned off, reverse current is blocked so
the SDIG output can be biased with an external source
when no power is present at IN. Leakage current is typ-
ically 3µA with 3.3V at SDIG.
LCD Boost DC-to-DC
In addition to the LDOs, the MAX1552 also includes a
low-current, high-voltage-boost DC-to-DC converter for
LCD bias. This circuit can output up to 28V and can be
adjusted with either an analog or PWM control signal
using external components.
SW provides an input-power disconnect for the LCD
when ENLCD is low (off). The input-power disconnect
function is ideal for applications that require the output
voltage to fall to 0V in shutdown (true shutdown). If true
shutdown is not required, the SW switch can be
bypassed by connecting the boost inductor directly to
IN and removing the bypass capacitor on SW (C9 in
Figure 1).
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