BQ25505: Measuring minimum input power for cold start

Juan Romero

Part Number: BQ25505

This question refers to the BQ25505EVM. I connected my board to a DC supply and the minimum voltage and current for the circuit to start (Vstor from 0 to 4V) is 0.54V and 3.57 mA. This would equate to 1.92 mW which is orders of magnitude higher than the 15 uW required for a CS according to the datasheet. Could you help me understand what I am missing or explain this situation? My goal is to harvest the 20uW available from a 100k load but at this point this is impossible. Also, I have noticed a pretty high leakage current but that is something I need to look further and may ask later. Thanks!

over 4 years ago

0 Jeff F over 4 years ago

TI__Guru**** 170526 points

Hi Juan,

The 15 uW typical value is incorrect and has not been updated since the minimum cold start voltage was increased from 330mV to 600mV. Your measured value seems a bit high. The test condition should be the minimum power to get VSTOR=1.9V and provide the Iq current (~400nA) into VSTOR (plus any leakage current into VSTOR capacitor and VBAT_SEC storage element).

Regards,

Jeff

0 Juan Romero over 4 years ago in reply to Jeff F

Prodigy 210 points

I measured the input power for VSTOR=1.9V and Vdc=0.352 and IDC=2mA. Roughly Pin=700uW. Again, could you help me understand what I am missing or explain this situation? I would like to harvest a minimum of 20uW, what would be the best approach/setup to achieve this?

+1 Jeff F over 4 years ago in reply to Juan Romero

TI__Guru**** 170526 points

Hi Juan,

We do not have the characterized value for minimum cold start power. It is likely much higher 20uW and could be the 700uW that you are measuring.

Regards,

Jeff

0 Juan Romero over 4 years ago in reply to Jeff F

Prodigy 210 points

I was hoping to use this IC but I understand... thanks for your time!

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BQ25505: Measuring minimum input power for cold start