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BQ76952: Issues with toggling DCHG/DDSG lines in BQ76952

Max Trybunksyi
Prodigy 70 points
Part Number: BQ76952


We are trying to control the DDSG and DCHG outputs that are driving the low-side FET driver circuit in our design. Unfortunatly we can't make it work. We assume that it could be caused by a proper register setting of the BQ76952 however we can't find what we are missing. Otherwise, it might be a hardware issue which is also not obvious to us.

When we enable the "Test mode", the DDSG_PIN and DCHG_PIN bits in the FET status are toggled but no change in the BQ76952 DDSG and DCHG outputs.

We also confirm that the 2 signals CFETOFF and DFETOFF are not working when we send pulses from the MCU.

Attached are all settings we use with highlighted yellow color the settings that seem to affect the DCHG/DDSG functionality. Let us know what might be wrong.

[1] Settings:

BQ76952_Parametrs-DDSG-DCHG.xlsx

[2] Schematic:
1031.SCH.pdf

  • TI__Guru* 81035 points

    Hi Max,

    Are you sending the DSGTEST() and CHGTEST() commands to enable the DCHG and DDSG pins? I tested your settings and the CFETOFF and DFETOFF pins are controlling the DCHG and DDSG outputs as long as these commands are sent first to enable the FETs. CFETOFF and DFETOFF can only disable the FET outputs, not enable them.

    I also recommend that you set the [FET_CTRL_EN] bit high in the FET Options register. This is not very clear in the current revision of the TRM, but it should be set high as long as the device is controlling FETs even if it using the digital outputs.

    Best regards,

    Matt 

  • in reply to Matt Sunna
    Prodigy 70 points

    Hi Matt,

    I can confirm that we did try all of your suggestions but no result. We can see that state changed in the register but no electrical signal change from AFE chip. 

    I asked one more team member to make a test with his set of PCBA samples and result should be in next days. 

    I'm wondering if there could be a hardware problem that does not allow signals to switch?

    Thank you in advance.

  • in reply to Max Trybunksyi
    TI__Guru* 81035 points

    It does appear the DDSG and DCHG pins are driving multiple driver ICs in parallel, It may be good to disconnect these ICs to see if the same behavior is seen.