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TPS61178: Maximum steady-state current for thermal stability

Joel Cottrell
Prodigy 50 points
Part Number: TPS61178

Hi TI staff, 

I have a 12-15V voltage booster PCB which uses the TPS61178 part. This works very well at low current, but is overheating in high load conditions.

The documentation seems to indicate that the current limits can be up to 10A, but I'm having trouble drawing more than 3A for any length of time, because the IC gets to 120+°C and cuts out. I can get it up to 5A if I improvise a small heatsink on top of the component, but it still doesn't get to the 7.5A that we require.

Is it possible that apart from the electrical limitations which set the max peak current, there is a maximum steady-state current that can be expected, due to thermal dissipation limitations? We would like to know whether we can ever expect this device to operate and keep cool at > 5A, or if we need to substitute a different part.

I do notice that your eval board is only set up for 2A, which makes me wonder whether I'm expecting too much from the small IC.

Many thanks,
Joel

  • 0
    TI__Mastermind 46905 points
    The 10A is the peak input current, not the output current. for a boost converter, the output current will be VIN*IIN*eff/VOUT. as the output voltage is higher than input voltage, the output current is lower than the input current. that is why the EVM is only setup to IOUT=2A.
  • 0 in reply to Jasper Li
    Prodigy 50 points
    Thank you Jasper for your reply. This is useful information; using that equation, our (15V) output will be limited to about 7.2A, (assuming 12V input and 90% efficiency).

    However, this doesn't really answer my question about thermals. Should it be possible for us to run the switcher at > 3A continuously without overheating, or can it only handle high current for very short durations?
  • 0 in reply to Joel Cottrell
    TI__Mastermind 46905 points
    the thermal performance depends on the PCB layout. if using four layer PCB and has GND panel helping the thermal dissipation, the device can support 6A average input current. the temperature rising in the EVM is approximately 40oC at 6A input current.
  • 0 in reply to Jasper Li
    Prodigy 50 points

    Our PCB does have 2oz copper GND planes on top and bottom, with via stitching as per datasheet instructions. There are two internal layers with planes, but they are connected to the Vin net, not GND. There may be a few small improvements that we could make, but I think the layout has been done quite well.

    In our application, your suggested limit of 6A input current would correspond to ~4A output, which approximately agrees with our experimentation. So this won't be sufficient if we need > 4A continuous output.

    Thank you for your assistance.