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BQ2205 noise switching from backup to main power

Wes Byers
Prodigy 410 points

I'm seeing an issue with the BQ2205 power monitoring and switching component. When switching from backup power to main, I'm getting quite a bit of noise on the output voltage. We're seeing an occasional loss of battery backed memory, and I'm trying to nail down the root cause. Our SRAM is IS62WV25616BLL-55TLI and has a retention voltage minimum of 1.2V, while I can see spikes during the transition getting close to that value. Our layout looks to be OK with bypass capacitors as close as possible to the VSS and power inputs to the BQ2205, but we only have a minimum 0.1uF bypass capacitors on the switch output close to the SRAM. Do we need bigger capacitance possibly located closer to the BQ2205? There isn't a recommendation in the data sheet that I can see.

Any recommendations would be greatly appreciated, I have a scope shot of the issue as well.

  • 0
    TI__Prodigy 410 points

    More information:

    I have the VOUT of the BQ2205 connected to two SRAM is IS62WV25616BLL-55TLI. Each SRAM has two 0.1uF 16V ceramic capacitors tied close to their VDD inputs. Could those capacitors be causing the issue? Does the BQ2205 require no capacitance. I don't see anything in the datasheet that indicates capacitors are needed.

  • 0 in reply to Wes Byers
    TI__Expert 4640 points
    Hi Wes,

    Unfortunately, this is an old device, and i would suggest that you use what the datasheet dictates. If there is no capacitance on the datasheet that is needed, i would go without caps.

    Miguel