LMZ12008: Load regulation problem

Hi Dhiman,

It will be fairly difficult to design the LMZ12008 to have such a tight regulation of 0.1%. The transient response shown in Figure 39 matches your application of Vin=12V, Vout = 5V with a delta_I transient of 7A. Even at this application, the regulation shows approximately ~180mV of output voltage deviation.

I'm curious to know what the application you are using the LMZ12008 in your system is for it to require such a tight regulation.

 Generally placement of your ceramic output bulk capacitor and high frequency output capacitor will help improve regulation. Output bulks should be placed close to the regulator while high frequency capacitor should be placed closer to the load to minimize trace inductance. Let me look into the module portfolio to see if there is anything that can meet your tight regulation. 

Regards,

Jimmy 

Hi Jimmy

The figure you have posted shows the transient response, I am considering the steady state response of load regulation of 0.1% as mentioned in the datasheet.

I am using the converter in power supply of automotive sensors where such tight load regulation (at steady state) is required. Please suggest any other product if LMZ12008 is not able to such regulation at 5A load.

Hi Dhiman,

Just to clarify you want a voltage ripple of no more than 5mV? Using WEBENCH Designer I simulated the Vin=12V, Vout=5V, Iout=5A steady state condition which results in a deltaV of 20mV. This simulation takes into account output voltage ripple and load regulation.  Is this also what you saw when you simulated the design? If you are reading a deltaV of around 100mV it might be because of PCB layout. 

 

The datasheet provides several Layout Guidelines (Section 10.1) that will help in PCB Design that will help with load ripple. Like you said previously, you can put post filter(LC) at the output of the module to improve voltage regulation. 

Regards,

Jimmy 

Hi Jimmy

1. Let me clarify about Load regulation at steady state not the voltage ripple. Load regulation is the load transient performance. Vout @ No Load - Vout@Full Load(5A) = 5mV at steady state.

More simplified way I want Vout=5V at no Load and Vout=4.995V at 5A Load condition at steady state.

2. In datasheet load regulation is mentioned as 1mV/A. In WEBENCH I have done the transient analysis but that does not give me my desired result.

3. I will try with post LC filter, If there is any design guideline for post LC filter design please provide. You can suggest me some other product portfolio for such specifications. 

Thanks

Dhiman

I want Vout=5V at no Load and Vout=4.995V at 5A Load condition at steady state.
In datasheet load regulation is mentioned as 1mV/A. In WEBENCH I have done the transient analysis but that does not give me my desired result. If there is any design guideline for post LC filter design please provide. You can suggest me some other product portfolio for such specifications.

Hi Dhiman,

I'd like to take this offline. Can you please provide your email so we can continue this dicussion?

Regards,
Jimmy

Hi Jimmy
Please communicate on following
Dhiman.Das@ee.iitd.ac.in
Thanks
Dhiman