TPS62175: Fail to output 5V

Datïan

Other Parts Discussed in Thread: TPS62175

Hi,

I use TPS62175DQCR converting 24V DC to 5V DC to power the RS-485 signal chain block with reference to TIDM-1005 REV E1. It doesn't work. I measured voltages at different pins. The voltages at pins of VIN and EN are 24.35V. The voltages at pins of VOS and SLEEP are 0.08V. I can not find the reason. Please help me to find out something wrong or missing in my design.

My schematic chart and pcb layout are shown as below.

best regards

Datïan

over 4 years ago

0 JohnTucker over 4 years ago

TI__Guru**** 191445 points

Datian,

The layout is not sufficient for a switching power supply. It will need to be re-done. Please see the layout guidelines and example in the datasheet.

0 Datïan over 4 years ago in reply to JohnTucker

Expert 1295 points

Hi John,

Many thanks for your help. I'm a newbie to this work. Do you mean I need to make my layout as identical as possible to the recommend example illustrated as figure 62 in datasheet of shown as below? And do you think my schematic is correct, especially the resistors connected to pin of FB ? The value of resistors are 787K and 150K ohm in section 9.3.3.1 of data-sheet. However, the respective value of resistors are 2M and 383K ohm in schematic of TIDM-1005 REV E1.

kind regards

Datïan

0 JohnTucker over 4 years ago in reply to Datïan

TI__Guru**** 191445 points

Datian,

Yes you should follow those layout guidelines. Switching converters require a specific layout technique of both component placement and routing of traces and copper pour areas. In addition to the above picture, you should also include a dedicated ground plane on an internal or bottom side layer. Make sure to include some thermal bias for the thermal pad to connect to this GND plane. Please see the EVM users guide for more details www.ti.com/.../SLVU743. Your schematic looks ok.

0 Datïan over 4 years ago in reply to JohnTucker

Expert 1295 points

John,

Thank you very much. I'll redo it.

Warm Regards

Datïan

0 Datïan over 4 years ago in reply to JohnTucker

Expert 1295 points

Hi John,

I'v redone my layout for a small part of TPS62175 in my original design. Would you mind to have a glance at my layout ?

Regards

Datïan

0 JohnTucker over 4 years ago in reply to Datïan

TI__Guru**** 191445 points

Data,

It is probably much better, but it is difficult to tell from the individual pictures. Can you stack them?

0 Datïan over 4 years ago in reply to JohnTucker

Expert 1295 points

John,

Thank you very much. Do you think it is necessary to enlarge the area of copper on top layer ? The size of this two-layer board is 6cm * 6cm. The thickness of copper is 1 oz.

Best Regards

Datïan

0 JohnTucker over 4 years ago in reply to Datïan

TI__Guru**** 191445 points

Datian,

I think that all looks ok. Let me know how it works when you get it built.

0 Datïan over 4 years ago in reply to JohnTucker

Expert 1295 points

John,

Sure, I will. Looks like weekend can not stop you from work as me :p

Best Regards

Datïan

0 Datïan over 3 years ago in reply to JohnTucker

Expert 1295 points

Hi John,

It works. The leds are lighted by 5V. Thank you very much for your powerful help. Do you think it is possible to reduce the area of copper if I choose 2oz as thickness of copper ?

0 JohnTucker over 3 years ago in reply to Datïan

TI__Guru**** 191445 points

Data,

In general you can reduce the area if you increase copper thickness. It is always a trade of of area vs thermal performance. Make sure there is enough copper in the current carrying traces to not cause too large I*R losses.

0 Datïan over 3 years ago in reply to JohnTucker

Expert 1295 points

John,

I got it. You rock.

Best Regards

Datïan

Power management

Power management forum

TPS62175: Fail to output 5V