PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
If the system is connected to a wall adapter, then the
voltage converters are powered directly from the adapt-
er through a 500mΩ load switch and the battery is dis-
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.
connected from the voltage converter inputs.
allows the system to operate regardless of the charging
state of the battery or with no battery.
This
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
AAT2601 will automatically shut itself down. (EN_KEY
and EN_HOLD are OR’d internally to enable the two core
converters.)
System Output (SYSOUT)
Intelligent control of the integrated load switches is
managed by the switch control circuitry to allow the
Step-down converter and the LDOs to have the best
available power source. When the CHGIN pin voltage is
above 4.5V, the system automatically turns on and the
power to the SYSOUT pin will be provided by either the
CHGIN pin or the BAT pin. When the USE_USB pin is
low, the CHGIN provides power to SYSOUT through an
internal LDO regulated to 3.9V. When the USE_USB pin
is high or if forced through use of an I2C command, the
BAT pin is shorted to SYSOUT through a 100mohm
switch. If a CHGIN voltage is not present and the sys-
tem is enabled, SYSOUT will be shorted to BAT.
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.
This system allows the step-down converter and LDOs to
always have the best available source of power. This
also allows the voltage converters to operate with no
battery, or with a battery voltage that falls below the
precondition trickle charge threshold.
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 AAT2601. 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 AAT2601
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.
Typical Power Up Sequence
The AAT2601 supports a variety of push-button or
enable/disable schemes. A typical startup and shutdown
process proceeds as follows (referring to Figures 1 and
2): System startup is initiated whenever one of the fol-
lowing conditions occurs:
1) A push-button is used to assert EN_KEY\ low.
2) A valid supply (>CHGIN UVLO) is connected to the
charger input CHGIN.
3) A hands free device or headset is connected, assert-
ing EN_TEST high.
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 AAT2601. 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 output capacitors and ensure a fast turn-off response
time.
The startup sequence for the AAT2601 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 start-
up sequence has commenced, LDO2 (PowerAnalog),
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2601.2008.01.1.0
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