LM5145: CV, CC control loop stability

user5069983

Part Number: LM5145
Other Parts Discussed in Thread: LM5117

Hello,

I am trying to design an CV, CC regulated battery charger with adjustable current level with LM5145. I have some troubles to get stable current regulation in my circuit, the current control loop is oscillating.

What has to be considered to get stable CC regulation (see the simplified schematic of my circuit)?

Are there any basic problems with the circuit?

Do I have to add a compensator zero in my CC control loop?

Design parameters:

switching frequency: 230 kHz

Vout max.=42 V

Iout: adjustable from 1A to 6A by microcontroller

Best regards

Florian

over 4 years ago

0 Timothy Hegarty over 4 years ago

TI__Guru 72622 points

Hi Florian,

Please see app note SNVA829 for more detail: https://www.ti.com/lit/an/snva829/snva829.pdf

Note that the LM5117 may be a more suitable controller as it enables a simple CC/CV circuit with its CM (current monitor) pin.

Regards,

Tim

0 user5069983 over 4 years ago in reply to Timothy Hegarty

Prodigy 60 points

Hi Timothy,

we already had contact in this case on Jan 12, 2021. I know the SNVA829 but the LM5117 is not suitable for my application (high duty cycle).

We have already chosen the LM5145 for the application. In the meantime I manged to get stability in my current control loop.

See circuit.

Maybe it can help someone.

I have absolutly no idea about the mathematics behind this circuit. Is there a way to get a statement about stability by measurement?

Is there someone who can derive the according rules of stability.

+1 Timothy Hegarty over 4 years ago in reply to user5069983

TI__Guru 72622 points

The easiest option for stability analysis here is with simulation. The LM5145 PSPICE transient model is available in the product folder: https://www.ti.com/product/LM5145#design-development##design-tools-simulation

From a practical standpoint, check the response with a load step and ensure it is well damped.

Regards,

Tim

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LM5145: CV, CC control loop stability