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TPS61220 Startup Issue

Mark Ackerson
Genius 10190 points
Other Parts Discussed in Thread: TPS61220

When powering TPS61220 from a bench supply or a battery simulator it often will not start correctly. There will be a high input current (20-50mA) and a 1V output (the design is for 2V out).

Using a zinc-air battery works, and connecting to a live supply mostly works.

Any ideas? We are thinking about adding a small series R on the input.  Schematic and scope plots below.

Bad Start Scope Plot

Good Start Scope Plot

  • 0
    TI__Mastermind 18285 points

    Mark,

    I'm moving your post to the correct forum. It looks like it belongs in the Non-Isolated DC/DC forum.

  • 0
    TI__Mastermind 46905 points
    the input voltage is too low in the "bad startup" scope. could you try
    1. other stronger power supply
    2. disconnect the 2V output with its load.
  • 0 in reply to Jasper Li
    TI__Genius 10190 points
    Hi Jasper,

    Both images are from the same supply. The first one is turning the output on with a switch, and has a slow rise time. You can see it takes 5mS to 500mV. The other one is fast, and would be similar to inserting a battery.

    Which means I shouldn't add a series R, as that would slow things down.

    Regards,
    Mark
  • 0 in reply to Mark Ackerson
    TI__Mastermind 46905 points
    the VIN (yellow line)of the first picture is much lower than the other one. i thinks this should be the root cause. the ramp up time should be not importance.

    what is the load condition in you measurement?
  • 0 in reply to Jasper Li
    Prodigy 30 points
    The load is minimal -- less than 1mA.

    Both setups are the same, bench supply set at:
    1.3V
    1A current limit
    6.8 ohm series R (to simulate zinc-air)

    The low voltage is due to the drop across the series R, and is in both images. It lasts longer in the first one as the supply fails to start, and the input current is sustained for a longer time.

    Curt
  • 0 in reply to Jasper Li
    Prodigy 30 points
    The load is <1mA

    Both setups are the same: 1.3V out, 1A current limit, 6.8 ohms series R to simulate zinc-air
  • 0 in reply to Jasper Li
    TI__Genius 10190 points
    Both were exactly the same setup for the supply:
    1.3V out, 1A current limit, series 6.8 ohm resistor to simulate zinc-air

    The lower voltage is due to the drop across the series R.

    The successful start-up has a fast rise time, since I plug in a connector to a live supply. You see that same drop, it just happens for a shorter period.

    The slow rise time is switching the supply output on from the front panel. It wouldn't be a concern, however we have other battery simulators that are showing the same symptom.
  • 0 in reply to Mark Ackerson
    TI__Mastermind 46905 points
    Mark
    i think the reason is that the EN has some delay.
    if device is connected to a live power supply, the CIN and COUT is charged to a higher voltage before device start to switching.
    if the device is powered on by switching the supply from the front panel, the device may start to switching at low input voltage condition.

    you can try to disable the device firstly, then enable the device after the input voltage is stable (VIN reach 1.3V). the device would startup more smoothly.
  • 0 in reply to Jasper Li
    Prodigy 30 points

    How do you recommend creating a delayed enable? We have tried a simple RC which works fine first time. However if we disconnect and then connect the input voltage again, the RC may not have fully discharged and then the power supply won't start correctly. 

  • 0 in reply to Curt McNamara
    TI__Mastermind 46905 points
    Hello Curt McNamara
    could you start a new post with the part number and the problem description? please detail the input/output condition. we can discuss the solution in the new post.