LP8725: PMIC 'BUCK2_FLAG MASK' bit issue

Aivaras,

I have assigned this question to the expert on this device, and I expect you will receive a response by end of day (US Central time).

Hi Aivaras,

Can you please provide a scope shot of this RESET_N behavior after disabling BK2_FLAG MASK? Please show at least the following signals:

1. RESET_N
2. EN
3. VIN2
4. Buck 2 output

Thanks,

Gerard

Attached is a trace of I2C write setting BK2_FLAG MASK bit to 0 and subsequent assertion of RESET_N 30ms later

PMIC_nRESET_OUT is LP8725 RESET_N [digital trace]

PMIC_EN is LP8725 EN/PWR_ON [digital trace – always high]

VDD_1V8 is LP8725 BUCK2 output voltage

PCIe_+3V3 is LP8725 VIN
The test jig used for this measurement is showing more noise than actually present on this voltage ..

Channel 5 and Channel 6 are LP8725 I2C interface

After a further 30ms there is a glitch on BUCK2 output voltage – is this PMIC restarting ?
[see second zoomed in waveform]

and after 30ms more RESET_N de-asserts ..

Hi Aivaras,

Thank you for providing additional details.

Please allow me some time to investigate whether we have any hardware to reproduce this behavior. I will get back to you with an update tomorrow. 

Thanks,

Gerard

Hi Aivaras,

Unfortunately we do not currently have hardware at our Dallas site. I am checking with our Finland team and will provide more information early next week. 

Thanks,

Gerard

Hi Aivaras,

I apologize for the delay. Our Finland team also did not have any hardware available, so we have scheduled a build of some EVMs to investigate this issue. 

Thanks,

Gerard