TPS55289: Iout-Limit is not working (as expected)

Michael Eichhorn

Part Number: TPS55289

Tool/software:

Hi there.

I'm trying to use the device for charging 12V Batteries from a 12V to 9V Source. The Device is controlled with a ATMega32U4 which is powered from the Vcc-LDO-Pin of the TPS55289. I'm going to limit the charging current to 1A by using a 10mOhm shunt and setting the register 0x02h to the value 0x94h, but the device is charging with 6A and runs into thermal shutdown after 10 seconds. I also tried to set the register 0x02h to 0x84h which should be 100mA but the current is still at 6A. The setting of the voltage is 12.9V at my test setup and it was stable with no load and also with a 100 Ohm resistive load. And of cause it fall down to battery voltage during charging condition.

Did I misunderstood the Iout-Limit function and it is not reducing voltage until current fits the limit register setting?

Or is the Internal LDO not capable for driving external load (like microcontrollers)? The datasheet told about 50mA load at the pin.

Hope you can help me.

Thanks and best regards

10 months ago

0 Mulin Yuan 10 months ago

TI__Genius 14950 points

Hi Michael,

Thank you for reaching out.

Do you mean TPS55289 is controlled by ATMega32U4, while ATMega32U4 is powered by TPS55289 VCC pin? TPS55289 VCC pin cannot be uesd to power external components.

When output current reaches the set limit value, the output voltage will start to reduce and output current is limited to the set value.

You can read the register value after you write it and check if it is correctly written.

Also, I please notice the current limit accuracy and evaluate if it is suitable for charger application.

Regards,

Mulin

0 Michael Eichhorn 9 months ago in reply to Mulin Yuan

Prodigy 40 points

Hi Mulin,

yes the ATMega is powered by the TPS55289 VCC-Pin. I expected this to be ment this way because of the 50mA specification.

I did read back the setting and the value is written correct into the register, but still ignored. Current is 6A in both tested settings (1A and 100mA).

0 Bryce Xun 9 months ago in reply to Michael Eichhorn

TI__Mastermind 27750 points

Hi Michael,

Thanks for feedback, we will look into this and reply to you later.

BRs,

Bryce

0 Mulin Yuan 9 months ago in reply to Michael Eichhorn

TI__Genius 14950 points

Hi Michael,

VCC current is used to power internal circuit. Don't use TPS55289 VCC to power MCU. There is risk that device cannot work normally.

Can you share schematic and read register value? I will check the design problem

Regards,

Mulin

0 Peter Kahn 9 months ago

Prodigy 40 points

In my experience, the TPS55289 doesn't support CC mode anyway. It just turns the output off when the configured output current limit is exceeded.

0 Mulin Yuan 9 months ago in reply to Peter Kahn

TI__Genius 14950 points

Hi Peter,

TPS55289 supports CC mode. It will reduce output voltage if output current limit is reached. Please refer to below figure.

Regards,

Mulin

0 Peter Kahn 9 months ago in reply to Mulin Yuan

Prodigy 40 points

Oops, yes, I tried again and CC mode works indeed. No idea what mistake I made when I tested that months ago.

0 Mulin Yuan 9 months ago in reply to Peter Kahn

TI__Genius 14950 points

Hi Peter,

I am glad that your issue is solved. I doubt that there is some misuse because theoretically CC function should work. I will close this thread. If you have any questions, feel free to reply and it will open again.

Regards,

Mulin

0 Michael Eichhorn 9 months ago in reply to Mulin Yuan

Prodigy 40 points

Hi Mulin,

I'm still working on it. Please wait.

0 Mulin Yuan 9 months ago in reply to Michael Eichhorn

TI__Genius 14950 points

Hi Michael,

No problem.

Regards,

Mulin

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TPS55289: Iout-Limit is not working (as expected)