BQ25505: Choosing vibration element

Nikos Antoniou

Part Number: BQ25505

Hi everyone,

We are designing a smart insole and we are willing to integrate energy harvesting (through step foot) as an auxiliary charging system. We have chosen the bq25505 charger and now we are investigating for vibration elements. We are looking for piezoelectric modules.

Do you have to suggest as any piezoelectric module for our application that would be compatible with bq25505? As I mentioned this is going to be just an auxiliary charging system and we're not looking to cover our full power load.

Thanks in advance

Nick

over 5 years ago

0 Jeff F over 5 years ago

TI__Guru**** 167196 points

Hi Nick,

Unfortunately, I do not have a specific vibration element. Keep in mind the charger must always boost so the VMPP << VBAT_OV<5.5Vmax. You will likely have to use a zener clamp on the element to protect the BQ25505 input.

Regards,

Jeff

0 Nikos Antoniou over 5 years ago in reply to Jeff F

Intellectual 820 points

Hi jeff,

First of all, thank you for your response!! However, I have some additional questions.

1. What you mean "charger must always boost"?

2. VMPP is the VOC_SAMP isn't it?

3. How did you choose Rsumoc = 20MΩ?

4. How did you choose VREF_SAMP = 0.14V?

Thanks in advance

Nick

0 Jeff F over 5 years ago in reply to Nikos Antoniou

TI__Guru**** 167196 points

Hi Nick,

1. The charger's VBAT_OV must be higher than the VMPP setting. If not, the charger turns on a FET to GND at VIN_DC to lower the input voltage and prevent battery overvoltage.

2. yes.

3. To prevent loading of the input source, we recommend 20Mohm but you can use lower resistor value. If you go higher, the leakage at the VOC_SAMP pin becomes an issue.

4. At the time, I recall a high Z source of some kind that had VOC=1V and VMPP= 0.14V.

Regards,

Jeff

0 Nikos Antoniou over 5 years ago in reply to Jeff F

Intellectual 820 points

Hi Jeff,

Thank you for the great answer. However, I think that there is a typo. VMPP should be 0.4V and not 0.14V

Nick

0 Jeff F over 5 years ago in reply to Nikos Antoniou

TI__Guru**** 167196 points

Hi Nick,

You are correct. I will record for next datasheet update.

Regards,

Jeff

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BQ25505: Choosing vibration element