My Customer is working a design using the bq21040 and there are a couple of questions regarding the ISET resistor.
1. The charger will be used to charge a small battery. Desired fast charge current is 35 mA. The Electrical Characteristics show the fast charge setting range is 10mA to 800 mA. However, several places in the texts mentions the charge range as 50 mA to 800 mA. Will the device support 35 mA? If so, I assume the KISET for this setting is 527 based on the spec table.
2. Assuming fast charge = 35 mA is OK, this would make the termination current = 3.5mA. Can the device detect this low current? There is no load other than the battery when charging.
3. I need more clarification on the ISET short test. The data sheet indicates the load current needs to be greater than 80 mA to detect a shorted ISET resistor. The power-up flow chart indicates there is a short test performed at 100 mA during power up. After power up, how is a short ISET resistor detected? It seems that if the Iset resistor shorts or drops in value during normal charge operation, the charge current will increase due to the lower resistance.If so, how long does a short detection take? With a charge current at 35mA, we are worried about overcurrent conditions.
