AAT2550 datasheet(21/35 Pages) ANALOGICTECH

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Data Timing

The system microcontroller should assert an active

low data request pulse for minimum duration of

200ns; this is specified by the SQPULSE. Upon sens-

ing the rising edge of the end of the data request

pulse, the AAT2550 status data control will reply the

data word back to the system microcontroller after a

delay defined by the data report time specification

TDATA(RPT). The period of the following group of data

pulses will be defined by the TDATA specification.

AAT2550

Total Power Solution for Portable Applications

2550.2006.07.1.0

Timing Diagram

SQPULSE

Data

System Reset

System Start

TSYNC

TLAT

N=1

N=2

N=3

TOFF

TDATA(RPT) = TSYNC + TLAT < 2.5 PDATA

TOFF > 2 PDATA

PDATA

Capacitor Selection

Input Capacitor

In general, it is good design practice to place a

decoupling capacitor between the ADP pin and

ground. An input capacitor in the range of 1µF to

22µF is recommended. If the source supply is

unregulated, it may be necessary to increase the

capacitance to keep the input voltage above the

under-voltage lockout threshold during device

enable and when battery charging is initiated.

If the AAT2550 adapter input is to be used in a sys-

tem with an external power supply source, such as

a typical AC-to-DC wall adapter, then a CIN capaci-

tor in the range of 10µF should be used. A larger

input capacitor in this application will minimize

switching or power bounce effects when the power

supply is "hot plugged."

Output Capacitor

The AAT2550 only requires a 1µF ceramic capac-

itor on the BAT pin to maintain circuit stability. This

value should be increased to 10µF or more if the

battery connection is made any distance from the

charger output. If the AAT2550 is to be used in

applications where the battery can be removed

from the charger, such as in the case of desktop

charging cradles, an output capacitor greater than

10µF may be required to prevent the device from

cycling on and off when no battery is present.

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