WEBENCH® Tools/LMR14030: LMR14030 output voltage drops with current load

BlueBill

Part Number: LMR14030

Tool/software: WEBENCH® Design Tools

We've built an LMR14030 supply using the reference schematic below. Problem is the output voltage drops with current load

e.g.

0A 5.06V

1A 4.48V

1.5A 4.35V

Any suggestions on why this is happening?

over 5 years ago

0 Gavin Wang (Zejing) over 5 years ago

TI__Expert 3480 points

Hi BlueBill,

What is input voltage?

Gavin

0 BlueBill over 5 years ago in reply to Gavin Wang (Zejing)

Prodigy 40 points

Hello Gavin

It's being supplied by 23 VDC @ 3A (Lab supply)

It also has a pair of low ESR 1500µF caps on the output.

0 Gavin Wang (Zejing) over 5 years ago in reply to BlueBill

TI__Expert 3480 points

Hi BlueBill,

In the post , you said " We've built an LMR14030 supply using the reference schematic below". There is only 47uF for the output cap. Why "It also has a pair of low ESR 1500µF caps on the output."?

Gavin

0 Andy Chen over 5 years ago

TI__Mastermind 27045 points

Hi,

Did you measure input and output voltage on Input or output cap terminal? can you upload actual circuit?

0 BlueBill over 5 years ago in reply to Andy Chen

Prodigy 40 points

This is the actual circuit, I've bypassed D1 & F1 for testing.

Scope across D6 with a 1A load shows 3.71V across the output caps.

0 Andy Chen over 5 years ago in reply to BlueBill

TI__Mastermind 27045 points

Hi,

Pls make below changes on your circuit:

1. L1=6.8uH

2. remove C13

3. C12=47nF

4. Place one 0.22uF 50V ceramic cap close to VIN pin and D6 GND

Test the circuit with E-load to see if output stable.

0 BlueBill over 5 years ago in reply to Andy Chen

Prodigy 40 points

Andy Chen said:

Hi,

Pls make below changes on your circuit:

1. L1=6.8uH

2. remove C13

3. C12=47nF

4. Place one 0.22uF 50V ceramic cap close to VIN pin and D6 GND

Test the circuit with E-load to see if output stable.

Thanks

Turned out the solution was the 0.22uF across VIN & D6 (I used a pair of 0.1uF caps as I have plenty), also I had to beef up the power traces on the 5.2V line.

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WEBENCH® Tools/LMR14030: LMR14030 output voltage drops with current load