AAT3603 datasheet(20/35 Pages) ANALOGICTECH

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AAT3603178

Total Power Solution for Portable Applications

PRODUCT DATASHEET

3603.2008.06.1.0

www .analogictech.com

The startup sequence for the AAT3603 core (Buck and

LDO1) is typically initiated by pulling the EN_KEY pin low

with a pushbutton switch, see Figure 1. The Buck (Core)

is the first block to be turned on. When the output of the

Buck reaches 90% of its final value, then LDO1 is

enabled. When LDO1 (PowerDigital) reaches 90% of its

final value, the 65ms RESET timer is initiated holding the

microprocessor in reset. When the RESET pin goes High,

the μP can begin a power up sequence. After the startup

sequence has commenced, LDO2 (PowerAnalog), LDO3

(TCXO), LDO4 (TX) and LDO5 (RX) can be enabled and

disabled as desired using their independent enable pins,

even while the Buck and LDO1 are still starting up.

However, if they are shut down, then LDO2, LDO3,

LDO4, and LDO5 cannot be enabled. The μP must pull

the EN_HOLD signal high before the EN_KEY signal can

be released by the push-button. This procedure requires

that the push-button be held until the μP assumes con-

trol of EN_HOLD, providing protection against inadver-

tent momentary assertions of the pushbutton. Once

EN_HOLD is high the startup sequence is complete. If

the μP is unable to complete its power-up routine suc-

cessfully before the user lets go of the push-button, the

AAT3603 will automatically shut itself down. (EN_KEY

and EN_HOLD are OR’d internally to enable the two core

converters.)

Alternatively, the startup sequence is automatically

started without the pushbutton switch when the CHGIN

pin rises above its UVLO threshold. The system cannot

be disabled until the voltage at the CHGIN pin drops

below the falling UVLO threshold. Thirdly, the EN_TEST

pin can be used to startup the device for test purposes

or for hands free operation such as when connecting a

headset to the system.

Typical Power Down Sequence

If only the battery is connected and the voltage level is

above the BAT UVLO , then the EN_KEY pin can be held

low in order to power down AAT3603. The user can initi-

ate a shutdown process by pressing the push-button a

second time. Upon detecting a second assertion of EN_

KEY (by depressing the push-button), the AAT3603

asserts ON_KEY to interrupt the microprocessor which

initiates an interrupt service routine that the user

pressed the push-button. If EN_TEST and CHGIN are

both low, the microprocessor then initiates a power-

down routine, the final step of which will be to de-assert

EN_HOLD, disabling LDO2, LDO3, LDO4, and LDO5.

When the voltage at the CHGIN pin is above the CHGIN

UVLO, the device cannot be powered down. If the voltage

at the CHGIN pin is below the CHGIN UVLO, both the

EN_KEY and EN_HOLD pins must be held low in order to

power down AAT3603. If LDO2, LDO3, LDO4, and LDO5

have not been disabled individually prior to global power

down, then they will be turned off simultaneously with the

Buck. The outputs of LDO4 and LDO5 are internally pulled

to ground with 10k during shutdown to discharge the out-

put capacitors and ensure a fast turn-off response time.

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