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[ ATL432B ] questions observed about the evaluation for comparator mode operation

Other Parts Discussed in Thread: ATL432

Hi Team

could you reply to my questions below about ATL432B's comparator mode operation ?

[1]  at Vref = 2.4V applied, I observed Ika = 11 uA.

      Ika = 11 uA is flowing because Imin(min cathode current for regulation) = Max 35uA spec ?

 

[2] I applied 10V for Cathode voltage. if I set Vref = 2.8V, I observed Vout was around 2V.

     if I reduce the current flowing into REF pin below 2 uA at Vref = 2.8V fixed,  Vout was increased to 10V.

     may I know why the current flowing into REF pin can affect ATL432B's comparator mode operation ?

     and what is the min current flowing into REF pin for ATL432B's best normal operation for ATL432B's comparator mode ?

 

[3]  I applied 10V for Cathode voltage. if I set Vref = 4V, I observed Vout was around 2V.

      at that time, I observed REF pin voltage around 2.6V ~ 2.7V.

      may I know why REF pin voltage was around 2.6V ~ 2.7V measured even if I supplied 4V ?      

 

  • Hello Paul,

    1. The current flowing into the cathode in comparator mode will be closely approximated by the curve Figure 5 from the datasheet. While the internal error amplifier isn't completely turning on the internal switch because Vref is not higher than the internal reference voltage, there will be some leakage into the cathode of the device.

    2. It is expected that the lowest voltage for this device in comparator mode will be close to 2V and not lower.
    I would expect that even a current of 2uA should properly bias the error amplifier to turn on the switch, I will have to set this up on the bench to test further to give a better estimate of the expected minimum cathode current as well as good margin to recommend that it be biased at.

    3. Are you using an Rin resistor? What value are you using?

    Best,
    Michael
  • Hi Michael

    for No 2 question, my test environment was as below.

        (experiment-1) under Vsup = 12V/Vin = 55V fixed/R1 = 14.4 Mohm/R2 = 710 Kohm, Vcathode was around 2V.

        (experiment-2) under Vsup = 12V/Vin = 55V ~ 76 V swing/R1 = 28.8 Mohm/R2 = 1.38 Mohm, Vcathode was around 12V.

                                at experiment-2, even if I increased VIn up to 76V, still Vcathode was 12V. I need to know why total resistor value affact ATL432 switch on

                                behavior.

    for No3 question, please also refer to below for set up.

    let me expect your swift reply. thanks.

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