BQ24105-Q1 Datasheet, PDF (11/35 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)

bq24105-Q1
www.ti.com................................................................................................................................................................................................. SLUS953 – AUGUST 2009
DETAILED DESCRIPTION
The bqSWITCHER™ supports a precision Li-ion or Li-polymer charging system for one-, two-, or three-cell
applications. See Figure 4 for a typical charge profile.
Regulation Voltage
Regulation Current
Precharge
Phase
Current Regulation Phase
Voltage Regulation and
Charge Termination Phase
V_LOW
Charge Voltage
V_SHORT
Charge Current
Precharge
and Termination
I_SHORT
UDG-04037
Precharge
Timer
Programmable
Safety Timer
Figure 5. Typical Charging Profile
PWM Controller
The bq24105 provides an integrated fixed 1MHz frequency voltage-mode controller with Feed-Forward function
to regulate charge current or voltage. This type of controller is used to help improve line transient response,
thereby simplifying the compensation network used for both continuous and discontinuous current conduction
operation. The voltage and current loops are internally compensated using a Type-III compensation scheme that
provides enough phase boost for stable operation, allowing the use of small ceramic capacitors with very low
ESR. There is a 0.5-V offset on the bottom of the PWM ramp to allow the device to operate between 0% to 100%
duty cycle.
The internal PWM gate drive can directly control the internal PMOS and NMOS power MOSFETs. The high-side
gate voltage swings from V_CC (when off), to V_CC – 6 (when on and V_CC is greater than 6 V) to help reduce the
conduction losses of the converter by enhancing the gate an extra volt beyond the standard 5V. The low-side
gate voltage swings from 6 V, to turn on the NMOS, down to PGND to turn it off. The bq24105 has two back to
back common-drain P-MOSFETs on the high side. An input P-MOSFET prevents battery discharge when IN is
lower than BAT. The second P-MOSFET behaves as the switching control FET, eliminating the need of a
bootstrap capacitor.
Cycle-by-cycle current limit is sensed through the internal high-side sense FET. The threshold is set to a nominal
3.6A peak current. The low-side FET also has a current limit that decides if the PWM Controller will operate in
synchronous or non-synchronous mode. This threshold is set to 100mA and it turns off the low-side NMOS
before the current reverses, preventing the battery from discharging. Synchronous operation is used when the
current of the low-side FET is greater than 100mA to minimize power losses.
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): bq24105-Q1
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