LM3677: Output voltage

li darren

Part Number: LM3677
Other Parts Discussed in Thread: LM3671, TPS82671

Hi,

I used LM3677 to design power module, there is only LM3677 in PCB, schematic is the same as datasheet, and test data as bleow.

over 100mA, device goto PWM mode, but the output voltage follows the current increase and decrease, 1.797@100mA, 1.767 @300mA, 1.742 @ 600mA, what is the reason for thar and what I can do?

Thanks for your help.

over 6 years ago

0 Ivo over 6 years ago

TI__Intellectual 880 points

Hello,

can you please check your measurement setup: please make sure that your voltage meter is not measuring a voltage drop on the PCB due to the load current.
Best regards,
Ivo

Texas Instruments

0 li darren over 6 years ago in reply to Ivo

Intellectual 520 points

Hi,

measured the voltage on output capacitance by multimeter。

0 Chris Glaser over 6 years ago in reply to li darren

TI__Guru*** 145550 points

Hi Li,

Can you post your PCB layout and identify where you measured the voltage?

0 li darren over 6 years ago in reply to Chris Glaser

Intellectual 520 points

Hi,

Mark on picture with black.

0 Chris Glaser over 6 years ago in reply to li darren

TI__Guru*** 145550 points

Thanks for sharing. Compared to the layout recommendation in the D/S, the output cap GND is far from the IC GND. You can order the LM3671 EVM and replace the IC and inductor to see what the load regulation is with a known good layout.

Also, do you see this behavior on 1 PCB or all?

0 Chris Glaser over 6 years ago in reply to Chris Glaser

TI__Guru*** 145550 points

As well, would the TPS82671 power module be a better fit for your application requirements?

Power management

Power management forum

LM3677: Output voltage