Part Number: BQ4050
Hi
I am working on a design that includes a BQ4050 and BQ25703A to provide power and charging to the system. They are to be controlled by a TPS65987, in a similar setup to TIDA-01515.
At the moment though I am trying to set the BQ4050 up but it seems to be responding strangely. I have the BQ25703A doing what I expect.
I am communicating with it via a microcontroller at the moment, which is connected to both the BQ4050 and BQ25703A. As far as I can tell the comms seem to be OK. I have checked with a scope and a logic analyser and all I2C/SMBus signals seem to be correct. I am able to read the registers but they are not all as expected. For instance the cell voltage 4 (0x3C) is always 0, whereas the cell voltage 1, 2 & 3 read correctly. Also the voltage (0x08) is always 2V.
Additionally, I am unable to charge the pack. I can set the BQ25703A up with a charge current and the default charge voltage (16.8V) but it seems the BQ4050 is not opening its charge FET as the pack voltage remains at 14.3V. I measure 5V on the charge FET gate, but the discharge FET has 13V going to its gate. Both are well over the on threshold (1.8V) of the FETs I'm using (CSD17308).
My question is, are there are basic configuration steps I need to take to set the BQ4050 up to work with 4 cells? I am not using BQ studio as I don't have a EV2400. I'm guessing that to write the settings to the registers, I will need to implement a CRC algorithm for the PEC. For the register reads that I have done so far, the BQ4050 has done this.
I can program the BQ4050 initially from a microcontroller but during running I want to have the communication to the BQ4050 coming from the TPS65987. The only regular piece of information I want to get from the BQ4050 is the relative state of charge (0x0D).
Another question is, will I be able to use the TPS65987 to read the relative state of charge from the BQ4050 on the TPS65987 I2C1 lines, then have the microcontroller read that value from the TPS65987 on the I2C2 lines.
I have attached the schematic that I am using for the BQ4050 and BQ25703A, which are mainly based on the TIDA-01515 schematic.
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