MAX8939EWVT datasheet(41/43 Pages) MAXIM

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______________________________________________________________________________________ 41

System Power Management

for Mobile Handset

Diode Selection

The OUT2 LED converter uses an external rectifier diode.

A Schottky diode is recommended due to its fast recov-

ery time and low forward voltage drop. Ensure that the

diode’s average and peak current rating exceeds the

average output current and peak inductor current. In

addition, the diode’s reverse breakdown voltage must

exceed the maximum VOUT2.

PCB Layout

Due to fast switching waveforms and high current paths,

careful PCB layout is required. Minimize trace lengths

between the IC and the inductor, the diode, the input

capacitor, and the output capacitor. Minimize trace

lengths between the input and output capacitors and

the MAX8939 ground terminal, and place input and

output capacitor grounds as close together as possible.

Use separate power ground and analog ground copper

areas, and connect them together at the output capacitor

ground. Keep traces short, direct, and wide.

Keep noisy traces, such as the LX_ node trace, away from

sensitive analog circuitry. For improved thermal perform-

ance, maximize the copper area of the LX_ and PGND_

traces. Refer to the MAX8939 Evaluation Kit for an exam-

ple layout.

Chip Information

PROCESS: BiCMOS

Typical Operating Circuit

MAX8939

DC/USB

USB

TRANSCEIVER

BROADBAND

PROCESSOR

DISPLAY

BACKLIGHT

KEYPAD

BACKLIGHT

CHG_MON

BATT

PWR_ON_CMP

SCL

SDA

IRQ

RESET_IN

LX2

OUT2

PGND2

COMP2

LED1

LED2

CHG

CHG_IN

SAFE_OUT

BATT

LX1

PGND1

COMP1

LED3

OPEN

1µF

10µF

1µF

10µF

Li+

BATTERY

2200pF

1µF

0.22µF

22µH

22µF

TO SYSTEM LOAD

OUT1

22µF

5V/700mA

AUDIO AMPLIFIER

VIBRATOR

LDO1

4.7µF

2.9V/400mA

LDO4

LDO1_EN

eMMC_EN

1µF

ANALOG 2.8V/100mA

MMC CARD

LDO2

22µF

DIGITAL SUPPLY

1.8V/200mA

ANALOG

2.8V/200mA

BLUETOOTH/FMR

COMBO, GPS

CAMERA

BATT

LDO3

22µF

PWM SWITCH

DRIVER

INVIB

1µF

OUTVIB

REF

AGND

1µF

DISPLAY

0.1µF

MAX8939EWVT Datasheet(PDF) 41 Page - Maxim Integrated Products

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