BQ24640: Using a supercap charger with Vin = 9 to 15VDC, Vout = Vcap = 8.0VDC, Icharge = 500mA

Jose Pompilha

Prodigy 20 points

Part Number: BQ24640

Hi,

I’d like to use the IC BQ24640 in my project with the following hardware characteristics:

Vin = 9.0 to 15.0VDC

Max Input Current = 700mA

Vout = 8.0VDC

Icharge = 500mA

Supercap = 4 x 55F @ 2.7VDC (serie)

Does BQ24640 meet my requirements?

When Vin = 9VDC the BQ24640 can assure my Vout to 8.0VDC?

The maximum input current from the source is 700mA and I cannot overcome this limit.

Could you help me to calculate the value of the inductor, RSR and output voltage regulation resistors?

Thank you!

over 7 years ago

0 Jing Zou over 7 years ago

TI__Mastermind 20570 points

You can use the tool in the link below for bq246xx related calculation.
www.ti.com/.../sluc175

For your configuration, if you set the OUT put regulation to 8V, you will not fully charge the super caps as it is 2.7V per cell total 10.8V with 4 in series.

0 Jose Pompilha over 7 years ago in reply to Jing Zou

Prodigy 20 points

Hi Jing Zou,

Thank you for your reply.

There is a misunderstanding, 2.7V is the voltage of the supercap. In my project each one will charge up to 2.0V and so Vcap = 8.0V. My question is, can I use this IC to meet all my requirements as I mentioned above considering the input voltage of 9.0V up to 15VDC?

Thank you!

0 Jing Zou over 7 years ago in reply to Jose Pompilha

TI__Mastermind 20570 points

Based on your description on output voltage at 8V, then it should be okay with 9V to 15V DC input.

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BQ24640: Using a supercap charger with Vin = 9 to 15VDC, Vout = Vcap = 8.0VDC, Icharge = 500mA