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SN65LVPE502A: Unstable power supply

Tao_2199
Genius 5660 points
Part Number: SN65LVPE502A
Other Parts Discussed in Thread: TUSB522P

Hello,

 

Regarding to power supply on SN65LVPE502ARGER, my customer is asking some question.

They use USB protocol analyzer for observe USB signal.

When power supply(Vcc) is unstable, LFPS(U1 exit) for recover from U1 state is not observed on USB protocol analyzer

.( It isn't output from SN65LVPE502A.)

If power supply(Vcc) is changed to LDO for improve quality , above problem is not happened. (LFPS(U1 exit) is sent from USB device LSI.)

They confirmed handshake between HostPC and USB device LSI.

Please refer attached diagram.

 


 

 

(Question)

(1) When power supply is unstable (like a in this case), what is the impact on Rx/Tx blocks in SN65LVPE502ARGER?

 

(2) According to datasheet, power supply range is 3.3 V ±10%. (3 to 3.6V : page6)

And the swing of power supply is within power supply range in case of problem .

Why is problem happened at this case? What point do we need to pay attention except power supply range?

 

(3) According to datasheet,, it seems to support USB 3.0 power management modes (low frequency periodic signals (LFPS) ).

Does it manage U1 state?

 

If so, how about the possible about the following hypothesis?

The device can’t recover from U1 state and it will transfer to incorrect state then the problem is happened on Rx/Tx blocks.

 

Regards,

Tao_2199

Power supply on SN65LVPE502.xlsx

  • 0
    TI__Mastermind 23815 points
    Hi Tao,

    LVPE502 is no longer recommended for new designs, please refer your customer to TUSB522P.
    The customer just may need to add AC caps, ferrite beads to have a stable Vcc.

    Regards
  • 0 in reply to Moises Garcia
    Genius 5660 points

    Hello Moises ,

     

    Thank you for reply.

    Since before NRND announced, they have been used this device.

    They have faced the problem on their application and have found out Vcc problem on LVPE 502A.

    So if possible, could you please answer previous their question?

     

    About AC caps and ferrite beads for stable Vcc,

    Could you please tell me these details in detail if possible?

    For example,

    Recommendation the value of capacitance, ferrite beads or schematic

     

    Regards,

    Tao2199

  • 0 in reply to Tao_2199
    TI__Mastermind 36085 points

    Hello Tao,

        We do not have a specific recommendation for ferrite, but the best practice is to include one 10uF capacitor for  VCC, one 0.1uF per VCC pin and one optional  0.01uF capacitor for VCC (total of four capacitors if you include the optional one).

    Regards,

    Diego.