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EM1402EVM: BQ76PL455A-Q1 EMB1499

Malcolm Mcdowell
Intellectual 570 points
Part Number: EM1402EVM
Other Parts Discussed in Thread: EMB1499Q

Hi,

I have a question on the DAC setting of the EMB1499,

From what I understand the EMB1499Q values for VSET range from 1V to 2.2V to indicate 2 to 5 amps of balance current. Is that correct?

That leads to a question about the DAC setting using the EMB_Vset() function. When I use the calculation for setpoint provided in this function which is:

int Setpoint = (int)(Amps/2.5/(3.2/256)) + 5;

The setpoint for the DAC will never result in a value greater than 5 (makes sense if this is the amp setting).After the SetPoint of 5 is programmed and I measure the pin  with a scope, "Vset"  on the EMB1499Q is only a few mV, It is not in the 1V to 2.2V range.

Should the Vset pin show a voltage of ~2V to indicate ~5amps?

Is this calculation of SetPoint correct or should the SetPoint  calculation change to, for example, send a SetPoint of 0x61 which makes the Vset pin show 1.20V

Thanks,

Malcolm

  • 0
    TI__Genius 9401 points

    Hi Malcolm,

    The balance current depends on both the VSET voltage as well as the Secondary Sense Resistor value, not only the VSET voltage. Please review the "Application Hints" section on the EMB1499 datasheet, page 14 with detailed description on how to choose the VSET voltage and the secondary sense resistor based on the balance current desired (http://www.ti.com/lit/ds/symlink/emb1499q.pdf ).

    Regarding how to set the DAC input, I recommend you first find the desired VSET value using the formulas in the datasheet, and then follow the DAC datasheet to define what inputs is needed. I reviewed the Setpoint formula in the software but I couldn't figure out where all the parameters are coming from. Have you tried setting the setpoint of 0x61 and confirm that gives you a Vset value of ~1.2V? This seems correct based on how Vout is calculated in the DAC datasheet. I would test this and check if you get the desired output. 

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    Intellectual 570 points

    Hi Leslie,

    Yes. When I set 0x61 I get the expected 1.2V.

    The highest I can set the voltage is  0x19 which is in the 200-300 mV range and I do see the charge cycle and current draw on my power supply. The battery voltage is increase but slow. If I adjust the ADC to anything above 0x19, the en pin goes high for only a short period (1 to 2 ms) and there is no error on the fault pins.

    I am try to understand this. I have to look at the value of the secondary sense resistor to see what it is. I am not sure what they used in the reference board, but I don't think it would limit the current to low levels.

    Not sure if you have any thoughts as to why this low voltage setting works, but not anything higher?

    Malcolm

  • 0 in reply to Malcolm Mcdowell
    TI__Genius 9401 points

    Hi Malcolm,

     "If I adjust the ADC to anything above 0x19"... Are you referring to the DAC setting?

    "Yes. When I set 0x61 I get the expected 1.2V"... So you do see this voltage but only for 1-2ms? What happens after? does the device keep charging every 1-2ms, or does the charging completely stop after 1-2ms?

    Regards,

    Leslie