TPS61032: Dual power application

David Gustavson50

Part Number: TPS61032

I am designing a device that can be battery powered or USB powered. If I set the output of the TPS61032 to 4.8V and also connect +5volts from the USB cable to the same net, will something bad happen, like current flowing backward through the TPS61032 to try to charge the battery? In a non-synchronous boost converter, I know the diode would prevent backward current and the boost converter would stop switching because the output voltage would be higher than the 4.8 volts. But since this is a synchronous converter, I don't know what would happen. I would prefer to use this chip because of the higher efficiency, if it will work.

Thanks,

Dave G.

over 5 years ago

0 Zack Liu over 5 years ago

TI__Mastermind 34201 points

Hi David,

When connecting +5volts from the USB cable to the same net, will you shutdown the boost converter by setting the EN pin low?

0 David Gustavson50 over 5 years ago in reply to Zack Liu

Prodigy 170 points

Hi Zack,

Yes, the plan is to disable the converter. However, the only thing I can sense is the level of the +5 volts. There may be ( and I should plan for) situations where the USB power is lower than expected and my detector does not disable the converter.

Thanks,
Dave G.

0 Zack Liu over 5 years ago in reply to David Gustavson50

TI__Mastermind 34201 points

Hi David,

It would be find because if setting the converter in shutdown mode, the load is completely disconnected from the battery.

0 David Gustavson50 over 5 years ago in reply to Zack Liu

Prodigy 170 points

Thanks, Zack.

What would happen if the converter were left enabled? This normally wouldn't happen, but it is possible the circuit wouldn't detect that the USB cable had been plugged in if the USB +5 were on the low side.

Thanks,

Dave G.

0 Zack Liu over 5 years ago in reply to David Gustavson50

TI__Mastermind 34201 points

Hi Dave,

What do you mean USB+5 were on the low side? Does this USB +5V still connect to output of boost converter?

0 David Gustavson50 over 5 years ago in reply to Zack Liu

Prodigy 170 points

Hi Zack,

Yes, the USB+5 is connected to the TPS61032 output. What will happen if for any reason, I do NOT disable the TPS61032?

Obviously, it would be desirable to disable the TPS61032, but I can't guarantee an absolutely foolproof way of detecting when the USB cable has been plugged in. I need to know what will happen in this worst case scenario.

Thanks,
Dave G.

0 Jasper Li over 5 years ago in reply to David Gustavson50

TI__Mastermind 46905 points

David

The device will stop switching if its output is higher than its setting output voltage. but the power save mode must be enabled.

0 David Gustavson50 over 5 years ago in reply to Jasper Li

Prodigy 170 points

I have already provided all the details you need. I don't think anyone can or will find the information I need. I will have to run some experiments myself. No one has answered my basic question:
If I leave the converter enabled, will current flow backward to the battery or backward to ground, yes or no?

0 David Gustavson50 over 5 years ago in reply to David Gustavson50

Prodigy 170 points

OK, I ran my own experiment. I powered the TPS61032 from 2 AA batteries with an amp meter in series. I put a 20 ohm load on the output. The current from the AA batteries was about .5 amps. Then I connected a bench supply in parallel with the TPS61032 output. If I adjust the bench supply above 5V, the current from the AA batteries drops to 0. There is even a small range where the bench supply and the TPS61032 share and I can adjust how much current comes from the bench supply and how much from the TPS61032. If I adjust the bench supply to 5.25V, the battery current does not change from 0, i.e. the current from the bench supply does not flow backwards and try to charge the battery. The current from the bench supply measures .27A, indicating the TPS61032 is not drawing any current either.

0 Jasper Li over 5 years ago in reply to David Gustavson50

TI__Mastermind 46905 points

Hi David
thanks for the summary and sharing. I found my reply is not clear enough. what I tried to say is "the IC stop switching and no current back to input side". And as I mentioned, the power save mode must be enable in this application.

I closed the post as you had found the answer.

0 David Gustavson50 over 5 years ago in reply to Jasper Li

Prodigy 170 points

Hi Jasper,

I did understand your first response, but I needed to know what happened if you did NOT put the converter in sleep mode. My experiment showed that there is no current back to the input side, even if the converter is enabled (not in sleep mode).

Thanks,

Dave G.

0 Jasper Li over 5 years ago in reply to David Gustavson50

TI__Mastermind 46905 points

Hi David,
What do you mean "sleep mode"? EN pin connected to low ?
What i were talking is at EN to high condition.

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TPS61032: Dual power application