BQ76952: Charger detect function

Hello Cheng,

Cheng Zhang said:

1. Charger detect in shutdown and deepsleep are triggered only if device sees an rising edge voltage at LD pin crossing 1.45V, which is an edge tiggered NOT voltage level triggered, correct? Any deglitch on this? And why set the threshold voltage this low, but not higher? I am concerned if the device will be waken up unexpectedly by some noise. 

Correct. LD's turn-on voltage is a rising edge on this pin. The part can be configured with an Auto-Shutdown feature, in case it turns on by mistake. This is described in Section 7.5 SHUTDOWN Mode of the Technical Reference Manual. This was set this low to account for low cell-voltage cases, where they may want to turn the device at very low voltages.

If the SHUTDOWN sequence is started, it will wait for the LD voltage to drop before entering SHUTDOWN.

Cheng Zhang said:

2. In sleep mode the charger detect function is triggered by PACK- TOP of stack voltage > pre-configured voltage delta, correct? Will it also triggered by the LD rising edge?

Correct. No, LD will not get the device out of SLEEP mode. LD is used solely for wake-up from SHUTDOWN.

Cheng Zhang said:

3. LD pin high voltage won't prevent the device from entering the sleep mode ,correct? E.g. LD pin is above 1.45V, the device go into sleep mode due to low current, will it immediately waking up due to LD pin above 1.45V?

Correct. The part can, and will go into SLEEP mode even if the LD voltage is above 1.45-V. 

Cheng Zhang said:

4. LD pin is also used for load detect feature, in a parallel MOSFET structure which means the charging path and discharging path separate, then the charger detect feature is unavailable if the LD pin on the discharging path for load detect feature?

No, the charger detect feature is actually part of the PACK pin. So in a separate charge/discharge path architecture, you would put the PACK pin to the CHARGER+ terminal and the LD pin to the PACK+/LOAD+ terminal (in order to get load detection). I'd recommend to read our  Parallel Paths with the BQ769x2 Battery Monitor application note .

Cheng Zhang said:

Finally, a similar question on the TS2 wake pin, is there any deglitch on this one? The datasheet says the pin weakly driven with internal 5V, what's the pull up resistance? 

The TS2 pin is pulled high by a ~4.5-MOhm pull-up resistor to 5-V (When in SHUTDOWN). This value is given in the datasheet. 

Due to its very high resistance, a small leakage current could potentially pull the pin down and cause the device to turn ON. So low-leakage switches should we used here if TS2 is used for wake-up from SHUTDOWN.

Hope this helped clarify things!

Best Regards,

Luis Hernandez Salomon