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TPS1HB50-Q1: Charge farad capacitor with tps1hb50-q1

SHENG YANG
Expert 1090 points
Part Number: TPS1HB50-Q1
Other Parts Discussed in Thread: TPS27SA08-Q1, TPS27SA08

ALL HI！

At present, there is a demand that DCDC outputs 12V voltage to charge farad capacitor (5F / 13.5V). If tps1hb50-q1 can meet the demand? Set the charging current threshold to 5A.thank you！

  • 0
    TI__Genius 16390 points

    Hi Sheng,

    Thanks for reaching out. It's hard for TPS1HB50 to support this unless there is a pre-charging circuit in place. If there's no current limiting resistor in the circuit, then during the pre-charge of the cap, the current will spike very high and hit the 5A limit which causes the FET to shut down.

    There are several ways to work around this:

    1. A pre-charging circuit uses a resistor and a relay, and the relay will close to short the resistor when pre-charge is finished.

    2. Another way is to set the current limit to be very high, then by changing the Ilim resistor values on the fly through an external FET to lower the current limit for normal operation.

    3. Set the current limit to be high constantly to save an external FET to control the current limit.

    4. By using one of the FET that has current clamp feature. TPS27A08 could be a good one.

    It's necessary for you to try out the solution before implementing it as the 5F cap is very large and there are chances that high side switch will reach thermal shutdown during the pre-charge phase due to the high current and high power dissipation. 

    Please let me know if you have additional questions.

    Regards,

    Yichi

  • 0 in reply to Yichi Zhang.
    Expert 1090 points

    HI!Yichi!

    Is there a vehicle specification chip similar to tps27a08? The current products are used in cars.

  • +1 in reply to SHENG YANG
    TI__Genius 16390 points

    Hi Sheng,

    Yes TPS27SA08-Q1 is available. Please let me know if this works for you.

    Regards,

    Yichi

  • 0 in reply to Yichi Zhang.
    Expert 1090 points

    HI!Yichi!

    If tps27sa08-q1 is used to charge the super capacitor (5F / 12V), I actually calculated that when the ambient temperature is 85 ℃, the time limit flow 1A will have thermal protection. Can you help me calculate the thermal power consumption? High and low temperature test ambient temperature - 40 ℃ ~ 85 ℃. Tps27sa08-q1 should not be able to meet the 2 ~ 3A current demand. thank you!

  • +1 in reply to SHENG YANG
    TI__Genius 16390 points

    Hi Sheng,

    I agree that charging a 5F cap is a challenge. Another part that can have better chance is TPS27SA08-Q1 which has 80A current limit threshold and allows current clamping. With 80A, the cap should be charged around 750ms. The transient thermal impedance is smaller during start-up, and the final temp would need to be integrated for the product of the cap charging curve (a straight line) and the thermal impedance curve below times 80A. 

    The best way is to order a EVM for TPS27SA08 and test out at site to see if it hits the thermal shutdown.

    Please let me know if you have additional comments.

    Regards,

    Yichi