Other Parts Discussed in Thread: BQ76PL455A
Hello,
I am currently using the EM1402EVM to charge and discharge various cells to a separate 12V source. However, I sometimes hear a high pitches noise when I believe the switch matrix is not connected to a cell, leaving Vplus and Vminus floating. I was wondering if this is normal, or if I should be worried that something is not operating properly. I am controlling the switch matrix SPI (with a FPGA) which is separate from the UART connection (via PIC Microcontroller). However, I am able to command both successfully. I am able to charge/discharge a given cell and see that cell's voltage change when polling the response from the BQ76PL455A. This leads me to think that I am correctly selecting the cell and charging/discharging from it, but after I send a "Open all switches" command to the EMB1428 connected to the charging/discharging cell, I hear a faint high pitch noise coming from the EM1402EVM.
Additionally, when I initially set VSET via the on-board DAC through SPI, I send a command to change its internal register to a value of 155, which should make VSET about 2V given that my VIO is 3.3V (which I have probed), but instead it sets VSET a voltage of almost zero (0.03V). Though when I send a value of 50, which should set VSET to (50/256*VIO) = 0.64V, I actually end up reading 1.48V on the DAC_OUT test point. I also don't believe it to be a timing issue/bit shift when writing the data, because if I send a raw value of 25, so half of what I sent to get the VSET to 1.5V, VSET does change to 0.75V. So by reducing the 8-bit value I write to the DAC's internal register by half, I see the same half reduction in the VSET. However, no matter what I do I am unable to get VSET to 2V.
So, I don't think these two problems are related, but I am not sure.
So,
1: Is it normal to hear a faint high pitched noise when operating the switch matrix? (either when it is connected to a cell or not)
2: Is there any additional steps I am missing that could be causing VSET to not abide by the equation given in the data sheet of (raw_value/256*VIO), or is my calculation simply incorrect?
Thank you in advance,
Russell Okamura