Dear Support,
I have designed a PM circuit to charge a battery using the BQ24073RGTR. Here is what it is doing:
- I connect USB host cable... 5V go into the BQ24073 VIN, and 4.4V comes out at Pins 11, and 10. (GREAT!)
- Both EN1, and EN2 are low to indicate 100mA draw from the USB host. Please note that USB host does not enumerate my device (missing firmware) to draw 500mA, so I am assuming 100mA max for this test since my load current is only 65mA.
-TD Pin15 is made low (enabled) via 10K external pull-down resistor so charge disabled is not constantly charging the battery
- CE_N is low via 10K pull-down resistor to enable charging with low current max 100mA (system load requires 65mA for battery)
-EN1 and EN2 are pull-down externally via 100K resistors pull-downs
- TS PIN 1 was changed from 49.9K to 10k pull-down since there is no thermistor.
- ILIM is set to 1.18K external resistor
-ISET is set to 5.90K assumes 750mAH battery with 0.2C charging (150mA)
-TMR is set to 47K resistor.
I see the voltage comes out regulated at 4.4V. I see PGOOD_N going low, and enabling a green LED on my board... I see CHG_N (pin9) going low indicating it is charging, but here is the sticky point... it is not... when I put a DMM in series with the battery positive terminal to measure the charging current into the battery, it reads 0A. I am also careful using the lowest DMM impedance to measure the current and not load the charger with additional resistance. In this case, no current is being delivered by the BQ24073 to the battery. I don't understand what could be wrong if all parameters appear to be in order (i.e., resistors and caps). Any idea as to why the charger would not charge the battery?
In the schematic below, R41 is 10K since there is no thermistor in the battery, and R42 is not installed in the actual board. Also, if this information helps, the battery I am using is a 2000mAH 22mOhms resistance for this test. I should be able to see current going into the battery for this quick and dirty test. The CHG_N light is low, and LED is on, but no current is flowing into the battery.
Please note that the source of power is the USB from a host. My load current is 65mA and I would expect 35mA into the battery when I have not negotiated 500mA from the host. I have tried putting a wall adapter capable of 500mA current, and in this case I would expect the full 150mA into the battery, and 65mA for the load (I should see 215mA drawn from the wall adapter). I only see 65mA indicating no charging.
I have also performed a test disconnecting the USB host cable from the board, while the battery is connected to the charger. When I disconnect USB host cable, I see current flowing from the battery into the load through the BQ24073 chip. This test result suggests the chip is handling the DPPM correctly and switches power correctly from one source and the other. The only issue is charging... I can't understand why it won't charge...
Attached is the schematic...
