Other Parts Discussed in Thread: CSD85302L
Hi there,
I am trying to test the discharge over current protection for the BQ29700SE but it doesn’t seem correct. Can you please help advise?
The following test was performed with the BQ29700 and power resistor are connected across the System +/- as the load to draw current.
Based on the formula provided in the spec, if I want to set my max discharge current to 250mA, then I should use a 0.4ohm resistor for Rext. So the PCM should cut-off if I am drawing above 250mA current, correct?
I connect the battery cell to the System+ pin and VSS pin, the battery voltage is about 4V and activated the PCM circuitry by shorting momentarily VSS and V- pins.
Test 1:
- I connect a power resistor about 25 ohms (current draw ~160mA), below the max discharge current
- The PCM remained functional while draining the battery slowly.
Test 2:
- I connect a power resistor about 10ohms as the load, so the current draw should be about 400mA, above the max discharge current.
- The PCM remained connected and the load continues to drain the battery quickly until the battery voltage is below the cut-off voltage (2.8V) before the PCM cuts-off.
- At this point, the battery is already down to 2V
Questions:
1. Why doesn’t the PCM cut-off when it is already beyond the max discharge current? It seems like the over-current protection doesn’t work ?
2. If i want to limit my max discharged current to only 100mA, I should increase my Rext to 1 ohm. Is there any downside to doing this?
Thank you.
HS
