ADP3408

REV. 0

–12–

YES

NO

YES

NO

CHGEN = HIGH

NIMH

CHARGING MODE

GATEIN = PULSED

VBAT > 5.5V

NIMH

CHARGER OFF

GATEIN = HIGH

VBAT < 5.5V

NIMH

LI+

YES

YES

NO

YES

YES

NO

NO

NO

NON-CHARGING

MODE

CHARGER

DETECTER

CHRIN > BATSNS

VBAT > UVLO

LOW CURRENT

CHARGE MODE

CHGEN = LOW

HIGH CURRENT

CHARGE MODE

VBAT > 4.2V

CONSTANT

VOLTAGE MODE

OF CHARGE

EOC = HIGH

TERMINATE CHARGE

CHREN = HIGH

GATEIN = HIGH

BATTERY

TYPE

Figure 5. Battery Charger Flow Chart

Digital Core LDO (VCORE)

The digital core LDO supplies the baseband circuitry in the hand-

set (baseband processor and baseband converter). The LDO has

been optimized for very low quiescent current at light loads as this

LDO is on at all times.

Memory LDO (VMEM)

The memory LDO supplies the peripheral subsystems of the

baseband processor including GPIO, display, and SIM interfaces as

well as memory. The LDO has also been optimized for low quies-

cent current and will power up at the same time as the core LDO.

Analog LDO (VAN)

This LDO has the same features as the core LDO. It has further-

more been optimized for good low frequency ripple rejection for

use with the baseband converter sections in order to reject the

ripple coming from the RF power amplifier. VAN is rated to

130 mA load, which is sufficient to supply the complete analog

section of the baseband converter such as the AD652l.

TCXO LDO (VTCXO)

The TCXO LDO is intended as a supply for a temperature-

compensated crystal oscillator, which needs its own ultralow noise

supply. VTCXO is rated for 5 mA of output current and is turned

on along with the analog LDO when TCXOEN is asserted.

RTC LDO (VRTC)

The RTC LDO charges up a capacitor-type backup coin cell to

run the real-time clock module. It has been designed to charge electric

double layer capacitors such as the PAS621 from Kanebo. The

PAS621 has a small physical size (6.8 mm diameter) and a nominal

capacity of 0.3 F, giving many hours of backup time.

The ADP3408 supplies current both for charging the coin cell

and for the RTC module when the digital supply is off. The

nominal charging voltage is 2.45 V, which ensures long cell life

while obtaining in excess of 90% of the nominal capacity. In

addition, it features a very low quiescent current since this LDO

is running all the time, even when the handset is switched off.

It also has reverse current protection with low leakage, which

is needed when the main battery is removed and the coin

cell supplies the RTC module.

SIM LDO (VSIM)

The SIM LDO generates the voltage needed for 3 V SIMs. It is

rated for 20 mA of supply current and can be controlled com-

pletely independently of the other LDOs.

Reference Output (REFOUT)

The reference output is a low noise, high precision reference with

a guaranteed accuracy of 1.5% over temperature. The reference

can be used with the baseband converter, if the converter’s own

reference is not accurate. This will significantly reduce calibration

time needed for the baseband converter during production.

Note that the reference in the AD6521 has an initial accuracy of

10%, but can be calibrated to within 1%.

Power ON/OFF

The ADP3408 handles all issues regarding the powering ON

and OFF of the handset. It is possible to turn on the ADP3408

in three different ways:

• Pulling the PWRONKEY Low

• Pulling PWRONIN High

• CHRIN exceeds CHRDET Threshold

Pulling the PWRONKEY low is the normal way of turning on the

handset. This will turn all the LDOs on, except the SIM LDO, as

long as the PWRONKEY is held low. When the VCORE LDO

comes into regulation the RESET timer is started. After timing

out, the RESET pin goes high, allowing the baseband processor

to start up. With the baseband processor running, it can poll the

ROWX pin of the ADP3408 to determine if the PWRONKEY has

been depressed and pull PWRONIN high. Once the PWRONIN

is taken high, the PWRONKEY can be released. Note that by

monitoring the ROWX pin, the baseband processor can detect a

second PWRONKEY press and turn the LDOs off in an orderly

manner. In this way, the PWRONKEY can be used for ON/

OFF control.

Pulling the PWRONIN pin high is how the alarm in the Real-Time

Clock module will turn the handset on. Asserting PWRONIN

will turn the core and memory LDOs on, starting up the

baseband processor.