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

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).

Complete Power IC for

Low-Cost PDAs

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Pin Description

PIN

NAME

FUNCTION

1

COR1

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

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

Ω pullup resistor from RS to MAIN.

7

LBO

Ω 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

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

16

MAIN