ADP3522 datasheet(16/20 Pages) AD

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REV. 0

–16–

ADP3522

HIGH CURRENT

3.2V

LOW CURRENT

4.2V

EOC CURRENT

EOC

INDICATOR

ICHARGE

VBAT

Figure 6. Lithium Ion Charging Diagram

Lithium Ion Charging

For lithium ion charging, the

CHGEN input must be low. This

allows the ADP3522 to continue charging the battery at the full

current. The full charge current can be calculated by using

CHR FULL

SENSE

() =

160

(3)

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 volt-

age, a constant 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 14 mV, then an

end of charge signal is generated—the EOC output goes high

(see Figure 6).

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 pin high and the

CHGEN pin high.

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

monitored through the MVBAT pin. The battery voltage is con-

tinually 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.

Battery Voltage Monitoring

The battery voltage can be monitored at MVBAT during charg-

ing and discharging to determine the condition of the battery. An

internal resistor divider can be connected to BATSNS when both

the digital and analog baseband sections are powered up. To

enable MVBAT, both PWRONIN and TCXOEN must be high.

The ratio of the voltage divider is selected so that the 2.4 V

maximum input of the AD6521’s auxiliary ADC will corre-

spond with the maximum battery voltage of 5.5 V. The divider

will be disconnected from the battery when the baseband sec-

tions are powered down.

APPLICATION INFORMATION

Input Capacitor Selection

For the input (VBAT, VBAT2, and VRTCIN) of the ADP3522, a

local bypass capacitor is recommended; use a 10

µF, low ESR

capacitor. Multilayer ceramic chip (MLCC) capacitors provide

the best combination of low ESR and small size but may not be

cost effective. A lower cost alternative may be to use a 10

µF

tantalum capacitor with a small (1

µF to 2 µF) ceramic in parallel.

Separate inputs for the SIM LDO and the RTC LDO are sup-

plied for additional bypassing or filtering. The SIM LDO has

VBAT2 as its input and the RTC LDO has VRTCIN.

LDO Capacitor Selection

The performance of any LDO is a function of the output capacitor.

The core, memory, SIM, and analog LDOs require a 2.2

µF

capacitor and the TCXO LDO requires a 0.22

µF capacitor.

Larger values may be used, but the overshoot at startup will

increase slightly. If a larger output capacitor is desired, be

sure to check that the overshoot and settling time are accept-

able for the application.

All the LDOs are stable with a wide range of capacitor types and

ESR (anyCAP

® technology). The ADP3522 is stable with

extremely low ESR capacitors (ESR ~ 0) such as multilayer

ceramic capacitors (MLCC), but care should be taken in their

selection. Note that the capacitance of some capacitor types

shows wide variations over temperature or with dc voltage. A

good quality dielectric, X7R or better, capacitor is recommended.

The RTC LDO can have a rechargeable coin cell or an electric

double-layer capacitor as a load, but an additional 0.1

µF ceramic

capacitor is recommended for stability and best performance.

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