LM5175EVM: LM5175 not turning on with 4.3V to 3.7V input

Ali Tatari38

Part Number: LM5175EVM
Other Parts Discussed in Thread: LM5175, LM2775

Hi ,

I am using LM5175 EVM SV601130B - My input voltage range is 3.7V to 4.3V. I have changed the enable resistor divider resistor R16 to 143K and R13 is 249K - this should allow EVM to start at minimum input of 3V .

The problem I am seeing is that it doesn't turn on till the voltage is at 4.35V - why is that happening?

over 5 years ago

0 Youhao Xi over 5 years ago

TI__Guru 68495 points

Hi Ali,

Thank you for using the LM5175. Please also read the datasheet: the min voltage at the VIN pin should be 3.5V. The EVM has an series diode at the VIN pin and that will reduce the voltage see by the VIN pin.

If you short this diode (D3), and at the same time Remove R28 from the EVM, you should start up at 3.5V. For 3V input, it is not guaranteed to startup because it is below the datasheet specifications.

Since your input voltage is low, you may consider to use charge pump device like the LM2775 to produce 5V and feed the 5V to the VIN pin, and the circuit should operate for your input range. For the EVM, you need to disconnect D3 and R28, and connect the LM2775's output to the VIN pin, and also connect the GND of the two circuits together.

Thanks,
Youhao Xi, Applications Engineering

0 Ali Tatari38 over 5 years ago in reply to Youhao Xi

Intellectual 470 points

Hi Youhao,
It reaches 9V when voltage at input pin is at 4V but when voltage at input pin between 3.5V and 4V it outputs max 5V. I have changed the enable R16 to 200K . R28 is removed , R34 is removed and R33 in feedback is 10.2K for 9V output

0 Ali Tatari38 over 5 years ago in reply to Ali Tatari38

Intellectual 470 points

What can we do to get 9V output when input is applied from 3.7V to 4.3V

0 Ali Tatari38 over 5 years ago in reply to Ali Tatari38

Intellectual 470 points

Actually at 3.5V at input pin then the output voltage is at 187mV

0 Youhao Xi over 5 years ago in reply to Ali Tatari38

TI__Guru 68495 points

Did you short he diode D3? It decreases the voltage at the VIN pin. Short it to make VIN pin see your 3.5V.

0 Youhao Xi over 5 years ago in reply to Youhao Xi

TI__Guru 68495 points

Hi Ali,

Any update? Can I assume the issue is resolved? We are required to close the thread if no activity for a few days. You can always reopen it by a new post.

Thanks,
Youhao

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LM5175EVM: LM5175 not turning on with 4.3V to 3.7V input