LMR23625: Could you check the Inverting power supply schematic?

teritama

Expert 1700 points

Part Number: LMR23625

Hi team,

Our customer design an Inverting power supply with LMR23625C.

When the load current is over about 100mA, the current consumption is over 1A.

We share the schematic in the follow figure. Could you check the schematic and comment concerned this issue?

design condition

Vin: 15V ＠ Regulated power supply
Vout: -10V
Iout: 700mA

note: When this issue occurred, we observed the Vout is -10V. And When there is no load, the device package become hot about 50-60℃.

If the Thermal PAD is not connected to PGND and AGND enough, is it possible the current flow the PAD or other root?

Best regards,

teritama

over 3 years ago

0 Andy Chen over 3 years ago

TI__Mastermind 27045 points

Hi Teritama

Pls try below:

Inductor L2=10uH

C148=50V rating, also parallel 0.1uF 50V

C150, 151,152=25V or higher rating

Pls upload PCB layout if problem still existing

B R

Andy

0 teritama over 3 years ago in reply to Andy Chen

Expert 1700 points

Hi Andy,

Thank you for reply.

I told to the customer to try to replace components and share the PCB layout and switching waveforms.

Please wait the result. We will let you know when we receive the result.

Best regards,

teritama

0 teritama over 3 years ago in reply to teritama

Expert 1700 points

Hi Andy,

First, we changed the available parts, L2 = 8.2uF and C148 to 50V rating. But the problem didn't solved. As soon as it become to be available, we try to change another parts.

And we share the PCB layout follow, it can seem the GND1 and GND2 are connected through via. Is this no problem for thermal characteristic?

Please some comment.

Best regards,

teritama

0 Andy Chen over 3 years ago in reply to teritama

TI__Mastermind 27045 points

Hi Teritama

The layout is not good enough:

1. C148--VIN--SW--PGND loop area is not small enough, try to add 5--10 ohm in series with C147 if problem still exist by moving C153 position

2, VCC cap I snot placed close to VCC pin

Pls solder C153 1uF as below

B R

Andy

0 teritama over 3 years ago in reply to Andy Chen

Expert 1700 points

Hi Andy,

Thank you for comments.

> try to add 5--10 ohm in series with C147
⇒Does this means add 5-10 ohm register between D52 cathode and C147?

>2, VCC cap I snot placed close to VCC pin
⇒In your figure, it seems that C154 is moved close to Vcc. Should we move C153 close to Vcc and keep C154?

Best regards,

teritama

0 Andy Chen over 3 years ago in reply to teritama

TI__Mastermind 27045 points

Hi Teritama

1. move either C154 or C153 to new place I as stated.

2. If problem still existing after re-place VCC cap, then try to add 5.1---10 ohm between C147 and D52 cathode (same node as IC Pin1 SW).

B R

Andy

0 teritama over 3 years ago in reply to Andy Chen

Expert 1700 points

Hi Andy,

I see. I'll tell the customer to try to replace the parts.

May I ask one question to understand?

Is adding the resistance 5-10 ohm to make some filter at SW node? I couldn't understand why add the resistance for large loop area and why resolve this problem by resistance.

Best regards,

teritama

0 Andy Chen over 3 years ago in reply to teritama

TI__Mastermind 27045 points

Hi Teritama

The Rboot resistor 5-10 ohm will limit the switch turn-on speed to reduce the ringing caused by improper PCB layout, this may helps the circuit to work stably with not so good layout design.

B R

Andy

0 teritama over 3 years ago in reply to Andy Chen

Expert 1700 points

Hi Andy,

Thank you for the answer.

I could understand Rboot resistor is for reduce the ringing.

I told the customer to try to replace. Please wait the result come.

Best regards,

teritama

0 Andy Chen over 3 years ago in reply to teritama

TI__Mastermind 27045 points

Ok, Let's wait customer update...

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LMR23625: Could you check the Inverting power supply schematic?