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TLV379: TLV379 in a Battery-Monitoring Application

HARINI KRISHNA
Expert 1905 points
Part Number: TLV379
Other Parts Discussed in Thread: TINA-TI, REF1112

Hi,

We want to have a battery voltage measurement circuit for Li-ion (NCR18650B) batteries with 3s2p configuration.

We found the resource online from TI https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2016/07/15/how-to-design-cost-sensitive-battery-monitoring-circuits on battery voltage measurement circuits.

The circuit was working as expected on Tina-ti software with TLV379 op-amp IC. (New Macros is TLV379)

 In the datasheet of TLV379  a battery monitor application circuit is given and we want to simulate the given circuit and choose the circuit which is best out of two.

  • Could you tell me how to calculate the Rbuffer and Rf values ?
  • What is REF1112 related to in the circuit diagram? 

On the Board we are measuring battery voltage using ADC (NRF52832).

  • Can you please guide on how to simulate the scenario of battery voltage measurement using ADC in Tina- ti software?

Thank-you

Warm Regards

Harini Krishna

  • 0
    Guru 140200 points

    Hi Harini,

    if you want to measure the battery voltage with an ADC, then the second circuit will not do what you want, I guess, because here the TLV379 works as a comparator. The REF1112 is generating a 1.25V reference voltage which is given to the -input of TLV379. R1 and R2 form a voltage divider to give a fraction of the battery voltage to the +input of TLV379. The OPAmp compares the two input voltages and as result the output of TLV379 toggles high or low. Rf provides a hysteresis (positive feedback) and stabilizes the switching, if the input voltages are almost equal.

    Kai 

  • 0 in reply to kai klaas69
    Expert 1905 points

    Hi Kai.

    Thank-you for the clarification.

    Can you please guide on how to simulate the scenario of battery voltage measurement using ADC in Tina- ti software?

    Thank-you

    Warm regards

    Harini Krishna

  • 0 in reply to HARINI KRISHNA
    Guru 140200 points

    Hi Harini,

    the usual approach is to add the equivalent circuit of ADC input to the output of TLV379 and to simulate whether the OPAmp is stable with this load. Also, it should be simulated whether the TLV379 is able to settle within the aquisition time of ADC. Eventually a charge kick back low pass filter has to be inserted between the OPAmp output and ADC input. With a bit luck the manual of ADC is already recommending such a circuit.

    Kai

  • Former Member
    0 Former Member in reply to HARINI KRISHNA

    Hello Harini,

    As Kai has mentioned, the second circuit shown is probably too simple for what you would like to do here because it's really only giving you a threshold.  If you're using an ADC, then you want to know the battery voltage itself.  To answer your question, however, the REF112 device will just provide a reference voltage, as Kai has also mentioned.

    Simulating the battery voltage measurement with ADC scenario is a bit more complex.  Again, Kai is right here.  The ADC in its entirety will be far too complex for TINA.  Instead, an equivalent input model is derived. TINA can then be used to determine whether the op amp going into the ADC is accurate enough, fast enough, and stable.  With SAR ADCs in particular, it's more common to use an op amp with a low pass filter in front of the ADC.  This low pass filter helps the amplifier to quickly change the voltage provided to the ADC.

    If you need help with this simulation, I recommend you watch the Texas Instruments Precision Labs series on ADC Input Driver Design.  It's a series of 7 videos that cover this topic in depth.  If you have further questions, I'd recommend you ask a new e2e question with your ADC device number.  Your question will get directed to the ADC team and they will be able to provide you with better support, since they work with these types of circuits all the time.

    Regards,

    Daniel

  • 0 in reply to Former Member
    Expert 1905 points

    Hi Daniel 

    Thank-you for the support

    Warm regards

    Harini Krishna

  • Former Member
    0 Former Member in reply to HARINI KRISHNA

    Hello Harini,

    I am happy to help.  Please let me know if I can be of any further assistance.

    Regards,

    Daniel