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TL431LI-Q1: Frequency response

Part Number: TL431LI-Q1
Other Parts Discussed in Thread: TL431, TL431LI

Hello TI Engineers,

I am using TL431LIBQ to design the feedback compensation network for single switch forward converter. I have two questions in this regard,

1. In the datasheet Fig. 6 there is the frequency response of TL431. Could you please explain what voltage gain does it refer to? And does this put some limit in the switching frequency of our power supply?

2. Also there is dynamic impedance vs frequency curve in Fig. 8 as below:

In datasheet dynamic impedance is mentioned to be around 0.3ohm to 0.75ohm but from Fig. 8 it seems this may vary with frequency. So do I need to take into consideration the switching frequency and then this impedance while biasing the TL431?

Thank you!

  • Hi Samir, 

    Before I explain your questions can you please tell me what is your switching frequency in your design? 

    Best Regards,

    Sila Atalar

  • Hi Sila,

    Thank you for your reply. It is at 300KHz. 

  • Hi Samir,

    This frequency response has been taken for VREF = VKA configuration. The flat band region shows that the device has good regulations capability and it will reject any noise coming in this region. The dynamic impedance plot also implies to similar thing.

    If there is any noise in the supply which is outside of the flat band region, TL431LI may not regulate it effectively in example the impedance will be more. You can think the dynamic impedance is equivalent to PSRR of a LDO. 

    Best Regars,

    Sila Atalar