BQ25173: Supercapacitor Value Suggestion For Our Application For BQ25173

Hello

Adi Tech said:

We require a device that can sustain operation for a 2-minute duration with an average current of 1A within a 5V system.

Can you tell me a little more about the requirements?

The BQ25173 max current is 800mA and your requirements is 1A.  Do you have any flexibility in this spec?

Some configurations to consider.:

1.) Two BQ25173 can be operated in parallel for more current

2.) A switching converter will be higher efficiency.  The BQ25173 is a linear and will reduce output current to manage thermal rise, switching converter does not have this issue.

3.) The BQ25173-Q1 (automotive version) has a bigger package and better thermal, can be run in parallel also.

Yes 800mA will work for us. But need to operate device for at least 2 minute. So, What Super capacitor value we select, to achieve our goal?

Adi Tech said:

We require a device that can sustain operation for a 2-minute duration with an average current of 1A within a 5V system.

Is the charge time for the super capacitor 2-minute?

A 20F capacitor would charge from 0V to 5V with an 800mA current in about 2-minute.

Hello,

Bill Johns said:

Is the charge time for the super capacitor 2-minute?

No This is discharge of supercapacitor, Charging time is not important for us.

we have continues power in our device from an AC Power Source, But this Power Source could be cutoff anytime, at power off time, we need to send data through GSM to our server, So after power cutoff we need 2 minute of time to send data through GSM, So device need to Operate for 2 minutes at 800mA of avg current, to send data to server. 

So What value you suggest for supercapacitor? and how many?

Adi Tech said:

No This is discharge of supercapacitor, Charging time is not important for us.

You need to support a 5V load at 1A for 2 min from a super cap.  

A DC to DC converter will be needed to take capacitor voltage and produce 5V something similar to below converter.

TPS62914 data sheet, product information and support | TI.com

Do you have a converter in your system already?

The BQ25173 will only charge the capacitor.

So What value you suggest for supercapacitor with BQ25173 ? and how many?

I estimate that you will need a 50F capacitor at 7.5V.  This could be 3 X 150F 2.5V capacitors in series, other configurations are possible.

This capacitor bank would feed a DC to DC converter, possibly TPS63060 buck boost.

This would give you 5V at 1A for 2 min.as capacitor discharges from 7.5V to 5V.

Below 5V the converter will enter boost mode and give you additional time but due to higher currents and lower capacitor voltage this will be less than a 1 min.

The BQ25173 can be used to charge the capacitor bank to 7.5V.

Thanks For this info, Could you share any calculation documentation for reference of above calculation.

I would like to work with you off line on this design.

The forum has a private massager feature and we can set up a conversation.