LMZ14203: Seeing sawtooth at output of Device

Dante Fasano

Part Number: LMZ14203

I have a design using a LMZ14203. The input is 24V, the output should be 5.5V. The simulation works fine. When I scope the output I see a 400mVpp sawtooth at about 5KHz.

The nominal DC value is 6V, not the set value of 5.5V. The 400mVpp sawtooth is riding ontop of the DC.

The FB node is incorrect too, at that same 5KHz frequency it spikes to 1V then settle back to the correct 0.8V.

Any ideas, it seems the control loop is not working

over 4 years ago

0 Jimmy Hua over 4 years ago

TI__Guru 50120 points

Hi Dante,

Can you provide the schematic for your design with the LMZ14203? 400mVp-p is considerably high for this device. Even for a 24Vin/3Vout at 3A operation, the output ripple should only be roughly 30mVp-p.

Regards,

Jimmy

0 Jimmy Hua over 4 years ago in reply to Jimmy Hua

TI__Guru 50120 points

Hi Dante,

May I get an update on this?

Regards,

Jimmy

0 Dante Fasano over 4 years ago in reply to Jimmy Hua

Prodigy 250 points

I found I had the Ron resistor connected to Gnd instead of Vin.

After fixing, the sawtooth is more like 35 mVpp.

0 Jimmy Hua over 4 years ago in reply to Dante Fasano

TI__Guru 50120 points

Hi Dante,

Thank you for the update and good to hear that the output ripple is closer to the expected 30mVp-p.

Did that solve your issue or do you still have any question regarding this part?

Regards,
Jimmy

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LMZ14203: Seeing sawtooth at output of Device