LMZ31710 Vin/PVin 12V Vout 5v, mulfunction

Bin Sun

Intellectual 360 points

Other Parts Discussed in Thread: LMZ31710

I used the circuit as the picture 1 which was proved by WEBENCH® Designer. But the output is like picture 2.

Power: 12V 2mA when no load. The output is between 2V and 4V, which should be 5V. The power good pin is pulled low.

Schematic

Output

The circuit board

over 8 years ago

0 Ulrich Goerke over 8 years ago

TI__Mastermind 40400 points

Hello Bin Sun,
Your questions should be posted in the Simple-Switcher Forum. I have referred your question to that group.
Regards,
Ulrich

0 Bin Sun over 8 years ago in reply to Ulrich Goerke

Intellectual 360 points

Thanks!

0 JohnTucker over 8 years ago in reply to Bin Sun

TI__Guru**** 191445 points

Moving to the Simple Switcher forum...but I can tell you that you are unlikely to get proper operation using that circuit board. You will most likely need a real pcb with copper pours and a ground plane. See the layout gudelines on page 26 of the datasheet.

0 J Arrigo over 8 years ago

TI__Mastermind 28020 points

Wiring the IC upside down on a bread board can lead to bad or missed connections. It is strongly recommended to mount to a PCB with the required footprint or evaluate with a web orderable EVM.

I did notice that pin 10 (PH) is not connected to the other PH pins. This connection is required and may help in your case.

0 Bin Sun over 8 years ago in reply to JohnTucker

Intellectual 360 points

Thanks, men.

0 Bin Sun over 8 years ago in reply to J Arrigo

Intellectual 360 points

According to the data sheet, the PH pins are for thermal relief. I didn't see why I must connect it.

I couldn't find a break board to solder on it. I am pretty sure I linked the pins and didn't miss any pin.

Any other idea?

Thanks men.

0 JohnTucker over 8 years ago in reply to Bin Sun

TI__Guru**** 191445 points

I do not support LMZ31710 directly, but this topic crops up from time to time. Switch mode power supplies require very specific PCB layout for proper operation. You may get poor or even non-operational performance even when using a real multi layer PCB if it is not designed correctly. I would be very surprised if you can get that to work with point to point wiring. I would suggest that you acquire an EVM to modify for testing your circuit if you do not want to design your own. You can locate it here:

www.ti.com/.../lmz31710evm-001

0 J Arrigo over 8 years ago in reply to Bin Sun

TI__Mastermind 28020 points

Pin 10 needs to be connected to the other PH pins on the PCB. This external connection must be made.

0 Bin Sun over 8 years ago in reply to J Arrigo

Intellectual 360 points

Get it.

Power management

Power management forum

LMZ31710 Vin/PVin 12V Vout 5v, mulfunction