BQ29200_16 Datasheet, PDF (8/24 Pages) Texas Instruments – Voltage Protection with Automatic Cell Balance

bq29200, bq29209
SLUSA52C – SEPTEMBER 2010 – REVISED MARCH 2016
8 Detailed Description
www.ti.com
8.1 Overview
The bq2920x provides overvoltage protection and cell balancing for 2-series cell lithium-ion battery packs.
8.1.1 Voltage Protection
Each cell voltage is continuously compared to a factory configured internal reference threshold. If either cell
reaches an overvoltage condition, the bq2920x device starts a timer that provides a delay proportional to the
capacitance on the CD pin. Upon expiration of the internal timer, the OUT pin changes from a low to high state.
8.1.2 Cell Balancing
If enabled, the bq2920x performs automatic cell-balance correction where the two cells are automatically
corrected for voltage imbalance by loading the cell with the higher voltage with a small balancing current. When
the cells are measured to be equal within nominally 0 mV, the load current is removed. It will be re-applied if the
imbalance exceeds nominally 30 mV. The cell mismatch correction circuitry is enabled by pulling the CB_EN pin
low, and disabled when CB_EN is pulled to greater than 2.2 V, for example, VDD.
If the internal cell balancing current of up to 15 mA is insufficient, the bq2920x may be configured via external
circuitry to support much higher external cell balancing current.
8.2 Functional Block Diagram
VDD
VC2
VC1
VC1_CB
GND
CB_EN
CB ^CB2_EN
Logic
CB1 _EN
CTRL
+
Hys.
–
+
–
5-V LDO
and POR
I_CD =
150 nA
CD
0.1 µF
OUT
8.3 Feature Description
8.3.1 Protection (OUT) Timing
Sizing the external capacitor is based on the desired delay time as follows:
td
C_CD = _XDELAY
Where t_d is the desired delay time and X_DELAY is the overvoltage delay time scale factor, expressed in seconds
per microFarad. X_DELAY is nominally 9 s/µF. For example, if a nominal delay of 3 seconds is desired, use a C_CD
capacitor that is 3 s / 9 s/µF = 0.33 µF.
The delay time is calculated as follows:
t_d = C_CD ´ X_DELAY
8
Submit Documentation Feedback
Copyright © 2010–2016, Texas Instruments Incorporated
Product Folder Links: bq29200 bq29209