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[TPS61029] the time from power on to PWM behavior

Takao Yamamoto
Genius 4135 points
Other Parts Discussed in Thread: TPS61251, TPS61252

Dear all,

Please help me, and teach me how long soft start time does this device have.

We hope this device to do PWM within 200ms after power on.

At attached file, Slide 1: our design circuit / Slide 2: Indications (transient behavior shortly after inserting battery) /

Slide 3: Unmount the buck up capacitor from board.

Question 1, Some items transit PWM behavior shortly after power on, but some items don't so.

                      What does raise this difference?

Question 2, Is there difference soft start time from item to item?

                      How different soft start from item to item?

Question 3, At slide 2 left side, why does PWM not start regardless of VOUT coming to near VIN?

Question 4, At our circuit, how long should we wait from power on to starting PWM behavior?

Best regards,

question.pdf

  • 0
    TI__Mastermind 46905 points
    please refer to the figure 12 of the datasheet's page 11, the device has limit pre-charge current during startup. the output current much be lower than the pre-charge current before the the device start to switching. in your application, the current to charge the bulk capacitor is large so the device delay switching.

    you can increase the current limit resistor (the 33ohm resistor) or change to larger pre-charge current device, like TPS61251 or TPS61252.
  • 0 in reply to Jasper Li
    Genius 4135 points
    Dear Jasper Li,

    Thank you for your reply and suggestion. I will try it.
    However I have three points to be checked.

    CHECK 1; Will this device start switching after VOUT coming up to about VIN? isn't it?
    However some of them will not start switching shortly after this. Why?

    CHECK 2; I cannot change this circuit design.
    So I would like to know how much pre-charge current variations this device have is.

    CHECK 3; Could you teach me the clear conditions to transit to switching?
    I set VIN = 4[V] and VOUT = 5.045[V].

    ***If you cannot reply something answer soon, please notice me the deadline you can suggest answer at first.

    Best regards,
  • 0 in reply to Takao Yamamoto
    TI__Mastermind 46905 points
    CHECK 1: I guess the device doesn't switching because the VOUT is not closed to VIN enough for some devices. as the voltage of the bulk capacitor increases, the VOUT will close to VIN enough, then the device start switching.

    CHECK 2: sorry, but We don't have test data of the pre-charge current variations.

    CHECK 3: the VOUT closed to VIN and output current is much lower than pre-charge current. ( or disconnect the bulk capacitor until the device start switching.)
  • 0 in reply to Jasper Li
    Genius 4135 points
    Dear Jasper Li,

    Thank you for your reply.

    However, I would like to know more details.

    Question 1;
    You said 'the VOUT closed to VIN', but could you teach me clearly condition?
    How value does VOUT come up to VIN?
    Could you teach me the worst condition of VOUT voltage to start switching?
    *For example, switching will start at minimum ○○ [V] of VOUT.

    Question 2;
    Could you teach me how long should we wait to start the latter system?
    At our circuit, we must decide the time to start of the latter system.
    Now, we design circuit to start within 250 [ms].
    However some devices don't start within 250 [ms], so the latter system can not wake up.
    I would like to know how long should the latter system wait to wake up in this circuit.

    Best regards,
  • 0 in reply to Takao Yamamoto
    TI__Mastermind 46905 points
    The device start to switching when diffenrence of VIN and VOUT is not higher than typical 150mV.

    had you tried to increase the resistor? does it work?
  • 0 in reply to Jasper Li
    Genius 4135 points

    Dear Jasper Li,

    Thank you for your reply.

    And I and my colleague would like to communicate with you by e-mail.

    I sent you direct message by E2E's friend request.

    I am looking forward  from hearing from you.

    Best regards,

  • 0 in reply to Takao Yamamoto
    TI__Mastermind 46905 points
    i had send you my email address through private message.