TPS54308: Load Transient Drop, Limited Source Current

Siddharth Gupta84

Intellectual 450 points

Part Number: TPS54308
Other Parts Discussed in Thread: TPS54302

Hi ,

My application is to generate GSM Supply of 4V from 24V.

Load Transient- 0 to 1.6 A

Duration: 577us

Limitation: Maximum Source Current Available: 200mA

Solution Required for: How to reduce drop @ position 3 (Refer Image attached) , Presently drop is 0.4V.

Changes Made:

Increased Inductor size from 15uH to 22uH.
Added feedback Capacitor 68uF to improve response.

Problem Faced: If voltage drop increases further (it drops to 3.76, if it drops below 3.6), the GSM IC restarts, and communication drops.

Regards,

Siddharth Gupta

over 7 years ago

0 Neal Zhang over 7 years ago

TI__Expert 4720 points

Hi,
here is some method you can try
1. increase the output cap from 22 uF to 47 uF or higher. This is the most easy way.
2. decrease Inductor value. Such as 15 uH or 10 uH.
3. the feedforward Capacitor 68pF is good.

0 Siddharth Gupta84 over 7 years ago in reply to Neal Zhang

Intellectual 450 points

Capacitors
22uF x 3 = 66 uF at present, Tested with six caps 132uF but not much of a difference in voltage drop.

Inductor earlier was 15 uF, changed it to 22uF to reduce ripple, didnot understand how reducing inductor size will reduce drop, as source is also limited to 200mA.
Pls explain.

Pls suggest should I further increase caps, presently using ceramics,will electrolutic help, or ny other change that could help to reduce voltage drop.

Regards,
Siddharth Gupta

0 Andy Chen over 7 years ago in reply to Siddharth Gupta84

TI__Mastermind 34775 points

Hi,

TPS54308 switching freq is only 350KHz, can you try higher freq part for better load transient performance?

0 Siddharth Gupta84 over 7 years ago in reply to Andy Chen

Intellectual 450 points

I have option of TPS54302 with 500KHz. Would that make a difference?

0 Neal Zhang over 7 years ago in reply to Siddharth Gupta84

TI__Expert 4720 points

Hi,
At first I think it's a load transient problem. So decrease inductor value and increase output cap value should help.
But since it doesn't help, maybe it's a steady state problem because of bad PCB layout. Could you help me do an experiment? Set Iout to be constant 1.6A, measure position 3. Then compare the voltage to see if it still has 0.4V drop.

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TPS54308: Load Transient Drop, Limited Source Current