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TLV61220: About input with super capacitor

Tao_2199
Genius 5770 points
Part Number: TLV61220
Other Parts Discussed in Thread: TL7770-5

Hello,

Regarding to input on TLV61220, my customer is asking some question.
Two super capacitor(2.2nFx2) are placed to input side of TLV61220.
These capacitor are used for backup at main power off
・Input: 4.2V, output: 5V
Please refer below schematics.


(Question)
In this case, the output is unstable for a while, and after that it is stable.
When output is set as 4.7V, this behavior is not happened.
(Please refer below.)



Could you please tell me possible reason about this behavior, if possible?
I think that it will be affected by two super capacitor.
Could you please give me some comment or advice?

Regards,
Tao2199

  • 0
    TI__Mastermind 46905 points
    what is green line in the waveform image? could you also share the layout and the inductor part number?
  • 0 in reply to Jasper Li
    Genius 5770 points

    Hello Jasper,

     

    I’m asking about PCB layout and the inductor part number to my customer..

    (1) The green line in waveform image means reset output.(TL7770-5, 2RESET)

    TLV61220 output is connected to input voltage (2VSU/2VSO) on TL7770-5.

    (Please refer below.)

    (2) The rate of problem on their boards :

    It's happened on 46 boards in total 53 boards.

    (3) Output current is approximately 220mA.

    Also I’m asking about waveform on FB,SW pin to them.

     

    Regards,

    Tao2199

  • 0 in reply to Tao_2199
    TI__Mastermind 46905 points
    please measure the VBAT, SW and VOUT waveform of the TLV61220. also zoom in the waveform so we can analysis what really happen.
  • 0 in reply to Jasper Li
    Genius 5770 points

    Hello Jasper,

     

    I have received some waveform captures and PCB layout form my customer.

    TLV61220_Vout.xlsxTLV61220_Vout_Probing.xlsxTLV6122_PCB_Layout.pdf

    (1)Waveform captures

    Please refer attached excel sheet. (TLV61220_Vout.xlsx)

    ･They have confirm that some switching noise is happened on signals depending on SW signal(Green) probing.

    Please refer attached excel sheet. (TLV61220_Vout_Probing.xlsx)

     

    (2)PCB layout

    Please refer attached diagram. (PCB_Layout.pdf)

    (3)Inductor（L1,4.7uH）information:

    Coilcraft EPL3015-472MLB

     

    (4) Additional information

    ･Vin=5V @ Supply voltage power on (from CN7 connecter.)

    ･This problem is happened both power on (from CN7 Vin=5V) and super capacitor input.

     

    Regards,

    Tao2199

  • 0 in reply to Tao_2199
    TI__Mastermind 46905 points
    hi Tao
    The schematic
    could you also try to increase the output capacitance? and also try to reduce the package size of the output capacitor to 0603.
    it seem unstable.
    please also note that the TLV61220 can't support 220mA output current, which is much higher than the capability of this device.
  • 0 in reply to Jasper Li
    Genius 5770 points
    Hello Jasper ,

    I informed to my customer your advice .
    Many thanks!

    Regards,
    Tao 2199