BQ25570: How to measure the impedance of the bq25570?

lee Peng

Intellectual 720 points

Part Number: BQ25570

How to measure the impedance of the bq25570 when it is working?

By R=V/I?

over 5 years ago

0 Ricardo over 5 years ago

TI__Genius 10385 points

Li Peng,

Are you referring to the input impedance bq25570?

Thanks,

Ricardo

0 lee Peng over 5 years ago in reply to Ricardo

Intellectual 720 points

Yes. Think it as a load, a resistor.

0 lee Peng over 5 years ago in reply to Ricardo

Intellectual 720 points

Hello？

0 Ricardo over 5 years ago in reply to lee Peng

TI__Genius 10385 points

Li,

The bq25570 operates in DCM (discontinuous conduction mode). The input current is pulsed to fulfill the MPPT setting. The device goes open circuit to sense the open circuit voltage and then pulses the input current to across the source resistance to regulate the input voltage at VIN_DC according to the MPPT setting.

So to solve for the average input impedance of the device, you must know the voltage at VIN_DC and measure an average input current. Then apply V=I*R to solve for R.

Thanks,

Ricardo

0 lee Peng over 5 years ago in reply to Ricardo

Intellectual 720 points

Thank you. So, can I insert a serial resistor R1 at the input of the bq25570. Therefore, I=V_R1/R1, R=V/(V_R1/R1) . Am I right?

0 Ricardo over 5 years ago in reply to lee Peng

TI__Genius 10385 points

Li,

It is recommended that you use a series resistor (~100 ohm) if you plan to use BQ25570 with a low impedance power source such as a bench top power supply. This value is different than the input impedance of the IC that is equal to RIN_DC(avg) = VIN_DC/IIN_DC(avg).

Thanks,

Ricardo

0 lee Peng over 5 years ago in reply to Ricardo

Intellectual 720 points

Thanks. My application is RF energy harvesting circuit. I indeed plan to use a bench top power source. I didn't get the mean of your last sentence. Did you mean using bench top power source, the result equals to RIN_DC(avg) = VIN_DC/IIN_DC(avg)?

0 Ricardo over 5 years ago in reply to lee Peng

TI__Genius 10385 points

Li,

I think we are talking about two different values. I have attached a drawing I think will help clear things up.

Thanks,

Ricardo

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BQ25570: How to measure the impedance of the bq25570?