BQ2085 Datasheet, PDF (19/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
SLUS541 – OCTOBER 2002
Table 11. Stand-Alone bq29311 Protection Control
MODE
CONDITION
Over Load
AFE Over Curr Dsg (DF 0xb2) is breached for Over Curr Delay (DF 0xb4)
Over Current
AFE Over Curr Chg (DF 0x0b3) is breached for Over Curr Delay (DF 0xb4)
Short Circuit, Discharge AFE Short Circ Thresh (DF 0xb6) is breached for AFE Short Circuit Delay (DF
0xb7, lower nibble)
Short Circuit, Charge
AFE Short Circ Thresh (DF 0xb6) is breached for AFE Short Circuit Delay (DF
0xb7, upper nibble)
NOTE 16: Clear is detected and controlled by the bq2085.
CLEAR (see Note 16)
AverageCurrent() = 0 mA
AverageCurrent() = 0 mA
AverageCurrent() = 0 mA
AverageCurrent() = 0 mA
SAFE Output
The SAFE output of the bq2085 provides an additional level of safety control. The active low safety output can
blow a fuse or control another switch on the basis of temperature, a programmable pack-voltage level, a
programmable cell-voltage level, or an integrity check of the AFE registers. The SAFE output is driven low in
any of the following 4 conditions if the AC bit in Misc Configuration (DF 0x2a) is set. If the SAFE output activates,
the bq2085 sets the SOV bit in pack status. SOV remains set until the bq2085 is reset. The SAFE output can
be pulled high (cleared) by a POR of the bq2085 only.
SAFE activation conditions:
D When any cell voltage > Cell Over Voltage (DF 0x60 and 0x61) AND after a minimum of 1s the pack voltage
> Safety Over Voltage (DF 0x68 and 0x69), or
D When any cell voltage > Safety Over Voltage (DF 0x68 and 0x69)
D When any cell voltage > Cell Over Voltage (DF 0x60 and 0x61) AND after a minimum of 1s the Temperature
> Safety Temperature (DF 0x6a and 0x6b)
D When Misc Configuration (DF 0x2a) bit 5 AC is set and the AFE has failed at least AFE Fail Times (DF 0xd3,
d4)
The bq2085 checks the programming of the AFE registers at a period determined by AFE Check Time DF 0xe4.
The units of the check period are seconds unless the bq2085 is in sleep mode, in which case the period is AFE
Check Time x Sleep Current Time (DF 0xe7). If the data is not correct, the bq2085 increments an internal
counter.
An example circuit using the SAFE output to blow a fuse is shown in Figure 5.
VCC
FUSE
Cell 4
BAT+
1 MΩ
0.1 µF
BSS84
SAFE
100 kΩ
1 MΩ
2N7002
Figure 5. Example SAFE Circuit Implementation
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