REV. 0

ADP3510

–13–

LOW CURRENT

CHARGE MODE

NONCHARGING

MODE

CHARGER DETECTED

CHRIN > BATSNS

NO

YES

VBAT > UVLO

BATTERY TYPE

END OF CHARGE

VBAT > 4.2V

EOC = HIGH

CHGEN = LOW

TERMINATE CHARGE

CHREN = HIGH

GATEIN = HIGH

VBAT > 5.5V

VBAT < 5.5V

NO

YES

NiMH

Li

YES

NO

NO

NO

YES

NO

YES

HIGH CURRENT

CHARGE MODE

CONSTANT

VOLTAGE MODE

CHGEN = HIGH

NiMH

CHARGING MODE

GATEIN = PULSED

NiMH

CHARGER OFF

GATEIN = HIGH

YES

Figure 6. Battery Charger Flowchart

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. Therefore,

the trickle charge current can be calculated by:

I

mV

R

CHR TRICKLE

SENSE

()

=

15

(3)

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 high current limit, 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.

Lithium Ion Charging

For lithium ion charging, the CHGEN input must be low. This

allows the ADP3510 to continue charging the battery at the full

current. The full charge current can be calculated by using:

I

mV

R

CHR FULL

SENSE

()

=

172

(4)

If the voltage at BATSNS is below the charger’s output voltage of

4.2 V, the battery will continue to charge in the constant current

mode. If the battery has reached the final charge voltage, a con-

stant voltage is applied to the battery until the charge current has

reduced to the charge termination threshold. The charge termination

threshold is determined by the voltage across the sense resistor.

If the battery voltage is above 4.0 V and the voltage across the

sense resistor has dropped to 12 mV, then an end of charge signal

is generated and the EOC output goes high (see Figure 7).

The baseband processor can either let the charger continue to

charge the battery for an additional amount of time or terminate

the charging. To terminate the charging, the processor must

pull the GATEIN and CHGEN pins high.

3.2V

ICHARGE

EOC

INDICATOR

VBAT

HIGH

CURRENT

4.2V

EOC

CURRENT

LOW

CURRENT

0

Figure 7. Lithium Ion Charging Diagram

NiMH Charging

For NiMH charging, the processor must pull the CHGEN pin high.

This disables the internal Li+ mode control of the gate drive pin. The

gate drive must now be controlled by the baseband processor. By

pulling GATEIN high, the GATEDR pin is driven high, turning the

PMOS off. By pulling the GATEIN pin low, the GATEDR pin is

driven low, and the PMOS is turned on. So, by pulsing the GATEIN

input, the processor can charge a NiMH battery. Note that when

charging NiMH cells, a current limited adapter is required.

During the PMOS off periods, the battery voltage needs to be moni-

tored through the MVBAT pin. The battery voltage is continually

polled until the final battery voltage is reached. Then the charge

can either be terminated or the frequency of the pulsing reduced. An

alternative method of determining the end of charge is to monitor

the temperature of the cells and terminate the charging when a

rapid rise in temperature is detected.