CHG_IN

 

 

3.6V

 

 

 

 

 

 

 

 

3.6V

 

 

 

 

50mA

 

C1

 

CHARGE FET

50mA

VCC

 

 

 

 

 

D1

+

 

MAX CURRENT

 

 

 

 

 

 

 

DETECTION

 

 

-

 

 

 

 

V REF1

 

 

SINGLE

 

 

 

 

CELL Li-ION

 

 

 

 

+

VOLTAGE

TIMER

BATTERY

 

 

SOURCE

TIMER

BATTERY

 

-

 

CHARGER

 

 

 

CHARGER

 

V REF2

 

 

CONTROL

 

 

 

CONTROL

 

 

TO

SUI

 

 

 

uPC

SUI

 

ADC

ADIN1

 

 

 

Figure 5.7-1 Typical application for pulse charging a battery

5.7.1 Charging Process

Figure 5.7-1 shows a typical battery charging implementation. The voltage source must be current limited (500 mA max). A reverse current protection diode prevents external fault conditions from draining the battery. A small (typ 10∝F) capacitor should be placed close to the CHG_IN pin.

In the application shown, a conditioning phase slowly raises the voltage of a deeply discharged battery cell to a level suitable for fast-charging. After cell conditioning is complete, the microprocessor uses the GR64’S ADC converter to monitor the cell’s status and uses the power management block to control the charge-FET.

A charge request is initiated when an external voltage source is applied to the CHG_IN pin. However, before this request is passed to the microprocessor, CHG_IN is verified to be greater than VCC by 150 mV, and at least 3.7 V. If the latter criteria is not met, the module limits charging to the conditioning phase. If the former criteria is not met, the charge request is ignored and all charging is disabled. If the CHG_IN voltage exceeds the upper limit of 6.3 V it will be detected by the module, but charging is not inhibited. In this case, however, CHG_IN is outside the normal operating range of the device, so the software will not initiate charging if CHG_IN > 6.3 V is detected.

The delta between CHG_IN and VCC is continuously monitored; however, the valid to invalid detection has a delay of 46 ms. When CHG_IN exceeds VCC by 150 mV, it is considered to be at a valid relative level. It is considered to have an invalid relative level if it subsequently falls below VCC by 50 mV. If the relative voltage of CHG_IN goes invalid and remains invalid for the duration of the detection delay, charging is terminated.

LZT 123 1834

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