UCD3138: How to design an antialiasinfg filter

Hi Noureddine Traiba,

Thank you for your interest in UCD3138. I have asked an applications engineer to take a look at your request.

Best Regards,
Ben Lough

Hi Ben Lough
I have a question about the requirement on the input signal at the ADC of UC31381
the background of question is : I need to design the filter for current and voltage sensing an to avoid the aliasing phenomena , but this features of this filter it depend on the sampling frequency ,ADC acquisition time, also the design of the closed loop control..... the idea is to have a LPF Sellen key, with RC filter for anti -aliasing
What the topology are used in TI for LLC Converter also for PFC converter using UCD3138 to avoid anti aliasing ?
thank you
Noureddine

Hi Noureddine Tariba,

An RC network should be sufficient for the ADC input. The bandwidth of the filter depends on how fast the response time needs to be for your design.

For reference, take a look at the UCD3138 LLC EVM (page 8)

for PFC, reference UCD3138 PFC EVM. You can see the filter on the control card schematic (page 4)

.

PMP20873 PFC reference design also might be useful to you.

Best Regards,

Ben Lough

Thank you Ben Lough

 In the refrence http://www.ti.com/lit/ug/sluu979a/sluu979a.pdf 

Thank you Ben Lough

In the refrence www.ti.com/.../sluu979a.pdf , why there are two RC filter one with high cut off frequency 1.592Mhz (R=100 Ohm , C=1000pF). and the other with low cut off frequency 79.58kHz (R=2KOhm, C=1000pF).
Could you please send me more details about the design of this filter and with paramaters are considered

thank you in advance
N.TARIBA

Hi Noureddine,

Apologies for the late response. It really depends on what you want to use ADC12 for. ADC12 is typically not used for loop compensation but for monitoring signals such as voltage, current, temperature, faults, etc. You want to consider the frequency of the signal you are sensing, how quickly you want the device to respond as well as what channel you are using. For example, a higher RC filter bandwidth is desired for the ADC channels connected to comparators. (reference page 3 of the datasheet:www.ti.com/.../ucd3138.pdf).

Best Regards,
Ben Lough