LMR16006: Why the chip re-startup when power off

user4681972

Part Number: LMR16006
Other Parts Discussed in Thread: TPS54360B,

Hello

I am using two LMR16006Xs to generate 5V 250mA and 12V 100mA. The input voltage is 36V. I am also using TPS54360B to generate 24V 0.8A. The figure below shows the shunt down waveform of 5V, 12V and 24V.

The yellow is 5V, green is 24V and red is 12V. blue is input voltage 36V. You can see the two LMR16006s are trying to re-start when power off and TPS54360B looks good. Take a look at the input, it was appeared when the input voltage drop below 3.8V where is close to the UVLO rising threshold. How to prevent the re-start? I attached the circuit.

Thanks

Chenyi Jiang

over 6 years ago

0 Samuel Jaffe over 6 years ago

TI__Mastermind 25590 points

Chenyi Jiang,

LMR16006 should not be able to try to start again if the input voltage is 0V. Please probe the input at the input of the LMR16006 and see if the input voltage is actually still present during these restarts.

-Sam

0 user4681972 over 6 years ago in reply to Samuel Jaffe

Prodigy 90 points

Sam,

I know LMR16006 will not re-start if the input voltage is 0V, but the actually input voltage will not fall to 0V quickly. It should fall slowly due to the capacitors, See the figure below, the green one is input of LMR16006, the yellow is +12V which restarts when the input is falling. And I measured the input voltage at +12V restart, it is around 3.5V.

Thanks

Chenyi Jiang

0 Samuel Jaffe over 6 years ago in reply to user4681972

TI__Mastermind 25590 points

Chenyi Jiang,

My mistake, I misunderstood the original blue waveform to be going to GND but it goes to 3.5V.

Yes, you can prevent this by utilizing the SHDN pin as UVLO. Connect a resistor divider from VIN to GND with SHDN connected to the node between the resistors. Check the datasheet table 7.5 under SHDN for the specs to calculate these values.

-Sam

0 user4681972 over 6 years ago in reply to Samuel Jaffe

Prodigy 90 points

Thanks Sam. It works.

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LMR16006: Why the chip re-startup when power off