TPS25942: Ramping time (dVdT) for Supercap charging 4.2V 3F

Hi ikon,

Could you please let me know your maximum operating ambient temperature.

Regards,
Rakesh

Hi Rakesh,

80C

Thanks.

Hi Rakesh,

3F Supercap needed to backup 3V8 and 3V3 voltage rails for 1sec when there is no input voltage.

Below are the measurements on the EVK:
Input Voltage, J3 = 4.2V
R13 = 0 ohm
R9 = DNP
C4 = DNP
Output Voltage, J2 = 3F Supercap
Current Limit = 2.1A (No Jumper)

From the measurement of Fault pin at 80C shown that the IC trying to auto-retry and successful to ramp up to 4.2V.

Is there any condition that IC unable to ramp up after auto-retry?

Thanks.

Thermal Imager of the IC when IC being heated up to 80C.pdf

Thermal Imager of the IC when inrush current drawn by supercap during start-up.pdf

Measure FAULT Response (pin 20) at room temperature.pdf

Measure FAULT Response (pin 20) at 80C.pdf

Hi ikon,

Thanks for the details and results.
I misunderstood on the max CdVdT capacitor mentioned in the Section 8.3 of datasheet. This max. limit is mainly to discharge the CdVdT capacitor before auto retry interval of 128ms.

You are free to choose bigger capacitor at dVdT pin to charge the super capacitor at a slower rate without entering the thermal shutdown.

For your specifications, I suggest to select 0.3A as charging current, which leads to ramping time of 42sec for 3F super capacitor. Corresponding CdVdT capacitor value is 120uF. Please test and revert back for any clarification.

Regards,
Rakesh

Hi ikon,

How this project is going? What are the final design values you are arrived at?
Do let us know if any review is required.

Thanks
Rakesh