AS3658F-BCTP datasheet(53/158 Pages) AMSCO

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AS3658

Data Sheet Confidential - Detail ed Descri ption-Power Management Functions

above the battery voltage. In case the AS3658 device is reset the charge controller will also be reset, even if a charge

adapter is applied to the VCHARGER or V_USB pin.

Charging deeply discharged batteries

To be able to charge even completely discharged batteries the AS3658 device contains an internal voltage regulator

that uses the voltage of the external charge adapter at pin VCHARGER or V_USB to generate a bootstrap voltage

V2_5V to supply the internal circuitry necessary for charging. As soon as the battery voltage exceeds 2.5V, the

bootstrap regulator is disabled and the battery voltage will be used to generate the internal supply voltage to supply the

charger circuitry.

Low current (trickle) charging

Trickle charge mode is started when an external charge adapter has been detected and ChEn or usb_chgEn is set,

and the battery voltage at pin V_BAT is below the ResVoltRise threshold VRESRISE. The Battery switch is open in that

case (batsw_on=1 batsw_mode=0). Bits ChAct and/or USBChAct and Trickle will be set in the Charger Status

registers. In this mode the charge current into the battery will be limited to TrickleCurrent (set in the Charger Current

of deeply discharged batteries. if Vsupply drops below Vsupply_min threshold the trickle current is regulated down, to

keep the Vsupply voltage up, even with an current limited charger (e.g.:USB charger). Once VRESRISE has been

exceeded, the battery switch will be closed and the charge controller will proceed to constant current charge mode.

The Vsupply voltage of the step down charger will be set to Vcurr_preset to prevent undervoltage on vsupply during

the transition between Trickle and constant current charging.

Constant current charging

Constant current charging is initiated by setting bit ChEn and/or USBChEn in the Charger Control register, and

resetting the No_charging bit. Note that ChEn and/or USBChEn should be set by default to enable operation of the

device without a battery connected to the system. The ChAct and/or USBChAct bit is set when the charger has started,

and the charge current into the battery will be limited to ConstantCurrent (set in the Charger Current register) by the

battery charge controller. When the battery approaches full charge, its instantaneous voltage will exceed the charge

termination threshold VCHOFF. VCHOFF depends on the ChVoltEOC.The top-off charge mode will be started (bit CVM

will be set).

Constant voltage charging

Constant voltage charge mode is initiated and the CVM bit will be set when the VCHOFF threshold has been exceeded

for the first time and bit Pulse is not set. In the following the charge controller will act to regulate the battery voltage to

a value set by ChVoltEOC in the Charger Config register.

The charge current is monitored during constant voltage charging. It will be decreasing from its initial value during

constant current charging and eventually drop below the value set by TrickleCurrent in the Charger Current register. If

the measured charge current is less than or equal to TrickleCurrent and the battery voltage is larger than VCHRES, the

charging cycle is terminated and EOC is set. Then the charge controller starts the EOC operation.

EOC operation

There are two possibilities:

1. If isolate_bat=1 the battery switch will be switch off and the battery charger regulates to its highest voltage Vchlimit..

The advantage of this mode is a longer lifetime of the Li+ battery, because there is no discharging after the EOC

condition. If autoresume=1 and the battery voltage drops below VCHRES the battery charger continues charging, by

checking in trickle charge mode, if there is a battery connected, and then starting with constant voltage.

2. If isolate_bat=0 the battery switch remains closed for step down charger or will be closed for linear and usb charger,

and the power to the system is supplied by the battery. The battery charger and the USB charger regulates to VEOC,

in case the battery is removed. If autoresume=1 and the battery voltage drops below VCHRES the battery charger

continues charging, by checking in trickle charge mode, if there is a battery connected, and then starting with

battery charging.

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