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TPS25947EVM: Inrush current for HDD

N.Z
Prodigy 20 points
Part Number: TPS25947EVM


Hi, we decided to use TPS259474LRPW for inrush current protection for hard disk.

We  are going to use efuse on both 12V and 5V circuit of the HDD.

I wonder how small the cout could be given that the one used in TPS25947EVM is 220μF.

Also, when tested using the module (TPS25947EVM) there was still voltage spike that's over the specification.

For 12V it's supposed to be more than 10.8V and lesser than 13.2V. Can you help with this?

What can I do to reduce the spike?

  • 0
    TI__Guru* 79181 points

    Hi Norisha,

    1. There is no minimum requirement of output cap. small cap like 1u-10u help in decoupling

    2. For your test how much is VIN, COUT and is any load connected?

    3. How long is your supply cable?

    4. You are testing on EVM?

    5 . Please share waveform like this with label:

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Hello Kunal.

    Thank you for the fast reply. I am sorry I was taking time to reply. Basically we're testing out hot swap for two SATA hard disk, which is connected by cable instead of pcb board to the motherboard. The 12V and 5V connection for the hard disk are from motherboard.

    The inrush current countermeasure circuit will be applied on the motherboard itself. which is why we decided to include TPS259474LRPW in the circuit. I bought only one EVM but since we have two connections (12V and 5V) we modified the circuit for EVM to test out the inrush current protection circuit on both 12V and 5V.

    CH1 is used for 5V connection and CH2 is for 12V connection.

    Also, to get more accurate result, we use the probe on the pcb board of hard disk to measure the voltage fluctuation.

    I tried to measured PG yesterday, but it's constant before and after turning the power supply on.

    The result we got earlier is when the power turned on and the hard disk is rotating for 40s, there were spike for voltage and it's more than the allowable voltage. I need to know the possible reason for the fluctuation even after adopting the EVM.

    Thank you.

  • 0 in reply to N.Z
    TI__Guru* 79181 points

    Hi Norisha,

    Just to confirm,

    1. You are giving external signal to EN pin of TPS2594 device?

    2. Have you shorted VIN1 and VIN 2 on EVM?

    3. Where are you seeing spike efuse VIN or VOUT.

    4. You turn on PSU and then power comes to EVM from motherboard, at that time you probe?

    As I said please share proper waveform that probes VIN,VOUT,EN and current through efuse to understand. The waveform you shared can you tell what each signal represent?

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Hi Kunal,

    1. Yes

    2. No

    3. It was at least after 3s after the disk was fully spinning.

    4. Yes, we have previous issue with inrush current appeared when the disk is spinning, not during hot swap.

    Also, another question, could you tell me the function of these diodes on channel 2 of the EVM?

    I thought diodes were already integrated into the eFuse?

    Thank you.

  • +1 in reply to N.Z
    TI__Guru* 79181 points

    Hi Norisha  ,

    1. This voltage line on which spike come it is channel1 or channel 2?

    2. This device can be  used at USB ports. So some one can accidentally apply USB at device output , so to limit VOUT to VIN voltage below abs max rating of device these diodes are used.