LM5163: LM5163 load response is terrible

David Gibbs

Prodigy 180 points

Part Number: LM5163

The circuit was designed in Webench Power Designer with the following specs:

Input:DC 7 V - 60 V

Output:5 V at 0.2 A

The circuit is attached.

Note that Vin is capacitively coupled (2200pF) from a wireless power transfer receiving coil and rectified, yielding about 13VDC unloaded (see scope shot below). The empirical inductance of my coil is about 25uH.

The first arrow on my scope shot corresponds to charging a battery at 50mA. The second arrow indicates charging at 100mA.

I'm at a loss as to why my transient response is so bad.

My scope shot:

Datasheet scope shot is below: note the nice transient response.

10 months ago

0 David Gibbs 10 months ago

Prodigy 180 points

I neglected to mention:

Pink trace = Vin

Blue trace = Vout

0 David Gibbs 10 months ago

Prodigy 180 points

Correction - coupling capacitor is 22,000pF not 2200.

0 Andrew Kutzler 10 months ago in reply to David Gibbs

TI__Genius 15380 points

Hi David,

Given that Vin is dipping that hard, there might be insufficient Cin. Also you probably want to add the 100nF high frequency bypass capacitor. Could you add those and report back.

Thanks,
Andrew

0 David Gibbs 10 months ago in reply to Andrew Kutzler

Prodigy 180 points

Hi Andrew,

I bumped Cin to 10u and added the 100nF. Vin looks like maybe 1V less delta at the 100mA charge point. I also have a bulk 47u AL cap on Vin. Should I try removing that due to the higher ESR that it must have?

Thanks,

David

0 Andrew Kutzler 10 months ago in reply to David Gibbs

TI__Genius 15380 points

Hi David,

Hmm. Generally high ESR Aluminum type bulk capacitors are recommended with these types of circuits. Definitely shouldn't cause a problem.

What happens if you just load Vin with a resistor? Is the circuit feeding our device stable? Does it feed enough power to the auxiliary circuit?

Also, what happens if you just have VIN replaced with 12V from a regular power supply?

Thanks,

Andrew

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LM5163: LM5163 load response is terrible