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TL431-Q1: Oscillation threashold

Shoo Saga
Expert 3566 points

Part Number: TL431-Q1
Other Parts Discussed in Thread: TL431LI-Q1, TPS3842-Q1

Tool/software:

Hi Team,

My customer has questions about TL431A=Q!. They need to report the OEM . Can we get the answer by EOD?

1.If violate the below minimum cathode current spec, the device will be unstable and oscillated?

2.Does the minimum cathode current spec comes from linear region in the image below?

3. What factor drives stability boundary below?

4. Can we simulate the open loop spec in case of the below cathode current spec? If can, Could you simulate it in IKa=0.3mA and 0.7mA? I cannot access my laptop.

Best,

Shoo

  • 0
    TI__Genius 13060 points

    Hi Shoo, 

    Thanks for your question! I have responded a similar question for TL431LI-Q1 earlier. Please refer to E2E for more information.

    1. A shunt reference is functionally similar to a Zener diode, where the voltage drop across the device is constant after the device reaches a minimum operating current. When the device is not getting the minimum cathode current, the output voltage will not be regulated.

    2. It's come from internal characteristics. When you think Zener diode, the device needs to be in it's reverse breakdown region. 

    3. If they want to add external output capacitor between the cathode and anode, they need to pick the correct value. The stability boundary graph helps them to find the correct values.  

    4. The minimum cathode current is 1 mA. Please find the alternative shunt references in below. 

    This table can be found in  Using the TL431 for Undervoltage and Overvoltage Detection. Since your customer is planning to use the device in open loop, the device is typically used as a comparator. 

    And please let me highlight if your customer needs cost efficient OV/UV monitoring, please check TPS3842-Q1. It's a Wide-Vin supervisor, and very popular device for it's simplicity.

    Best,

    Sila