ADP3522 datasheet(15/20 Pages) AD

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ADP3522

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Applying an external charger can also turn the handset on. This

will turn on all the LDOs, except the SIM LDO, again starting

up the baseband processor. Note that if the battery voltage is

below the undervoltage lockout threshold, applying the adapter

will not start up the LDOs.

Deep Discharge Lockout (DDLO)

The DDLO block in the ADP3522 shuts down the handset in

the event that the software fails to turn off the phone when the

battery voltage drops below 2.9 V to 3.0 V. The DDLO will

shut down the handset when the battery falls below 2.4 V to

prevent further discharge and damage to the battery.

The DDLO will also shut down the RTC LDO when the main

battery is removed. This will prevent reverse current from dis-

charging the backup coin cell.

Undervoltage Lockout (UVLO)

The UVLO function in the ADP3522 prevents startup when the

initial voltage of the battery is below the 3.2 V threshold. If the

battery voltage is this low with no load, there is insufficient

capacity left to run the handset. When the battery is greater

than 3.2 V, such as inserting a fresh battery, the UVLO com-

parator trips, and the threshold is reduced to 3.0 V. This allows

the handset to start normally until the battery decays to below 3.0 V.

Once the system is started and the core and memory LDOs are

up and running, the UVLO function is entirely disabled. The

ADP3522 is then allowed to run until the battery voltage

reaches the DDLO threshold, typically 2.4 V. Normally, the

battery voltage is monitored by the baseband processor, which

usually shuts the phone off at a battery voltage of around 3.0 V.

If the handset is off and the battery voltage drops below 3.0 V,

the UVLO circuit disables startup and puts the ADP3522 into

UVLO shutdown mode. In this mode, the ADP3522 draws very

low quiescent current, typically 30

µA. In DDLO mode, the

ADP3522 draws 15

µA of quiescent current. NiMH batteries can

reverse polarity if the 3-cell battery voltage drops below 3.0 V,

which will degrade the batteries’ performance. Lithium ion bat-

teries will lose their capacity if overdischarged repeatedly, so

minimizing the quiescent currents helps prevent battery damage.

RESET

The ADP3522 contains a reset circuit that is active both at

power-up and power-down. The

RESET pin is held low at

initial power-up. An internal power good signal is generated by

the core LDO when its output is up, starting the reset delay

timer. The delay is set by an external capacitor on RESCAP:

RESET

RESCAP

=×

(1)

At power-off,

RESET will be kept low to prevent any baseband

processor starts.

Overtemperature Protection

The maximum die temperature for the ADP3522 is 125

°C. If

the die temperature exceeds 160

°C, the ADP3522 will disable

all the LDOs except the RTC LDO. The LDOs will not be

re-enabled before the die temperature is below 125

°C, regard-

less of the state of

PWRONKEY, PWRONIN, and CHRDET.

This ensures that the handset will always power off before the

ADP3522 exceeds its absolute maximum thermal ratings.

Battery Charging

The ADP3522 battery charger can be used with lithium ion

(Li+) and nickel metal hydride (NiMH) batteries. The charger

initialization, trickle charging, and Li+ charging are imple-

mented in hardware. Battery type determination and NiMH

charging must be implemented in software.

The charger block works in three different modes:

1. Low current (trickle) charging

2. Lithium ion charging

3. Nickel metal hydride charging

See Figure 5 for the charger flow chart.

Charge Detection

The ADP3522 charger block has a detection circuit that deter-

mines if an adapter has been applied to the CHRIN pin. If the

adapter voltage exceeds the battery voltage by 100 mV, the

CHRDET output will go high. If the adapter is then removed

and the voltage at the CHRIN pin drops to only 50 mV above

the BATSNS pin, CHRDET goes low. The CHRDET signal is

not asserted if the battery voltage is below the UVLO threshold.

Trickle Charging

When the battery voltage is below the UVLO threshold, the

charge current is set to the low current limit, or about 10% of

the full charge current. The low current limit is determined by

the voltage developed across the current sense resistor. There-

fore, the trickle charge current can be calculated by

CHR TRICKLE

SENSE

() =

(2)

Trickle charging is performed for deeply discharged batteries to

prevent undue stress on either the battery or the charger.

Trickle charging will continue until the battery voltage exceeds

the UVLO threshold.

Once the UVLO threshold has been exceeded, the charger will

switch to the default charge mode, the LDOs will start up, and

the baseband processor will start to run. The processor must

then poll the battery to determine which chemistry is present

and set the charger to the proper mode. Control of the charge

mode, Li+ or NiMH, is determined by the

CHGEN input.

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