BQ77910 CHG pin no 12V output.

An over-current test or event can result in large transients when the discharge FET turns off with load.  Testing a product design thoroughly to be sure the protector is operated within its abs max limits during the events is advised.  If the protector IC does not work after the test, some troubleshooting is required.

In a development environment, it may be possible to connect the GUI and communication interface and poll the bq77910 status. 

If the part will not respond to the status poll, check to see if it has shut down by measuring the VREG voltage. If the over-current event causes a fast rise of the BAT pin voltage, the part may shut down. If this is the case be sure the capacitors are close to the BAT pin. It may be necessary to change the circuit to reduce the BAT pin rise time. Other extreme signal conditions may also cause a device shut down. These may have to be explored by inspecting signals on repeated events. Signals driven excessively below VSS may be a key concern for shut down.

If the status still shows the over current fault, check for recovery conditions. See if the current has actually stopped, the part will not recover if it still senses a voltage on the current sense pins above the threshold. Check for a residual load which might prevent detection of load removal. If the voltage on DPCKN does not fall below the recovery threshold, the part will not try to turn on the CHG output. Also if the device has SOR = 1, charger detection is required for recovery. Since you did not mention the DSG not coming on, you have likely checked these conditions.

If the status shows an over-voltage or under-voltage condition that is not confirmed by a check of the cell voltages, suspect a transient may have come past the product's transient protection circuit and input filter and damaged an input.  Check for unexpected voltages across the input resistors or low/high voltages between adjacent VCx pins.

If the status shows OK, suspect a transient from the event may have damaged the output driver. It can be difficult to predict what is damaged, but perhaps varying levels of damage could occur to one or more of the CHG, CPCKN, CCAP and BAT pins depending on the circuit configuration and the level of the transient.  Depending on the circuit configuration, you may be able to discharge through the charge FET to get an estimation of the transients before replacing the device.

Hi WM5295:

      I have according to your requirement to do it. connect the GUI and communication interface and poll the bq77910 status,I find the status shows an over-voltage, measurement the battery voltage,It show 4.14V per cell.EEPROM set OVT is 4.225 and OV Hysteresis is 100mV.So I discharge 10 min,Test again,It show Ok and Chg voltage output 12V.

Thank you for your reply.

John xiao 2011.07.26