BQ24618_15 Datasheet, PDF (15/43 Pages) Texas Instruments – System Power Selector and Low

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8 Detailed Description
bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
8.1 Overview
The bq2461x is a stand-alone, integrated Li-ion or Li-polymer battery charger that accommodates USB
applications with a minimum input voltage of 4.7 V. It employs a switched-mode synchronous buck PWM
controller with constant switching frequency. The device controls external switches to prevent battery discharge
back to the input, to connect the adapter to the system, and to connect the battery to the system using 6-V gate
drives for better system efficiency. The bq2461x features Dynamic Power Management (DPM) which reduces
battery charge current when the input power limit is reached to avoid overloading the AC adapter when supplying
current to the system and the battery charger simultaneously. A highly accurate current sense amplifier enables
precise measurement of input current from the AC adapter to monitor the overall system power. The input current
limit can be configured through the ACSET pin of the device.
The bq2461x has a battery detect scheme that allows it to automatically detect the presence and absence of a
battery. When the battery is detected, charging begins in one of three phases (depending upon battery voltage):
precharge, constant current (fast charge current regulation), and constant voltage (fast charge voltage
regulation). The device will terminate charging when the termination current threshold has been reached and will
begin a recharge cycle when the battery voltage has dropped below the recharge threshold (V_RECHG). Precharge,
constant current, and termination current can be configured through the ISET1 and ISET2 pins, allowing for
flexibility in battery charging profile. During charging, the integrated fault monitors of the device, such as battery
overvoltage protection, battery short detection (V_BATSHT), thermal shutdown (internal T_SHUT and TS pin), safety
timer expiration (TTC pin), and input voltage protection (V_ACOV), ensure battery safety.
The bq2461x has three status pins (STAT1, STAT2, and PG) to indicate the charging status and input voltage
(AC adapter) status. These pins can be used to drive LEDs or communicate with a host processor.
Regulation Voltage
V_RECH
Regulation Current
Precharge
Current
Regulation
Phase
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Termination
Charge
Current
VLOWV
I_PRECH
and
I_TERM
Charge
Voltage
Precharge
Time
Fastcharge Safety Time
Figure 13. Typical Charging Profile
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