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LM74722-Q1: Schottky diode for absorbing the negative spikes

Vishwas H R
Prodigy 240 points
Part Number: LM74722-Q1
Other Parts Discussed in Thread: LM74800-Q1

Hello,

Actually i need output at Pin C and at VOUT. My absolute maximum rating of other IC is -0.3V.

What is your recommendation on choosing the schottky diode? Also, do i need to place one more schottky diode in parallel to Pin C?

How the negative spike is generated at output and what will be the path and maximum current?

  • 0
    TI__Guru 57737 points

    Hi Vishwas,

    The Schottky diode is only required is the output voltage swings negative. This can only happen when the  load current is interrupted (PD turn OFF) and there is inductance in the output path. If there is on inductance in the output path the schottky across the OUT to GND is not required. 

  • 0 in reply to Praveen GD
    Prodigy 240 points

    okay got it, if there is a inductance after the VOUT, then we need a schottky diode so that when Q2 is off the output inductance will cause a negative spike and reverse current shouldn't flow from source to drain of Q2 and also it shouldn't damage the Q2.

  • 0 in reply to Vishwas H R
    TI__Guru 57737 points

    Hi Vishwas,

    The inductance will cause the voltage at the output of LM74722-Q1 to negative. For LM74722-Q1 it is okay even if the output Swings negative as there is no connection between the output power path and the controller.

    But for other devices like LM74800-Q1 the output is connected to OUT pin of IC which is not rated for negative voltage. So, for devices like LM74800-Q1 a Schottky is definitely required when there is an inductance at the output.  

  • +1 in reply to Praveen GD
    Prodigy 240 points

    Hi Praveen,

    yeah since we have zener diode as recommendation for VGS protection for Q2, even i feel the schottky diode is not required for absorbing negative spikes across output for LM74722-Q1.