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UCC23513: current capacity for output stage NMOS body diode

Emma Wang
Expert 4710 points
Part Number: UCC23513
Other Parts Discussed in Thread: UCC21551,

Tool/software:

Hi team,

please kindly help to check the current capacity for output stage NMOS body diode, My customer want to know that.

Beside, there is a ESD structure for the output pin, if there is a positive voltage on VEE-VOUT, Will the ESD take over the current first? And the VOUT pin spec, min value is VEE-0.3V, if it is violated? The ESD diode will have the risk to broke? 

BR

Emma

  • 0
    TI__Genius 15856 points

    Hi Emma,

    There are only two output states: LOW and HIGH

    In the output LOW state, the NMOS is closed, and the the body diode is shorted out. The output saturation current is +/- 5.3A. If the output dV/dt is fast enough, and there is a long Vgs to gate driver loop, you might observe some high frequency LC resonance and undershoot across the parasitic inductance through the Vee and Vout pins.(Usually this is only possible with a faster rise time device like UCC21551, not UCC23513). However the internal V(Out) -V(vee) on the die stays at 0V, and there is not risk of damage to the low-side NMOS. However, you might start to create overvoltage across the high-side devices if the undershoot is low enough.   

    In the output HIGH state, the low-side NMOS body diode is reversed biased, and only conducts only a small leakage current. The path of least resistance to the output is through the high-side PMOS, and the Roh is 9.5 Ohms.

    If your customer is nervous, it is always helpful to have a TVS diode across the gate driver supplies to prevent overvoltage, since this is the most common cause of damage. 

    Best regards,

    Sean

  • 0 in reply to Sean Cashin
    TI__Expert 4710 points

    Sean,

    My customer add an diode on Vout to VEE, but they found the diode will always broken(short)

    https://www.semiee.com/file/backup/LRC-LRB501V-40T1.pdf, it is a 100mA diode? do you think it is normally enough?

    and how about UCC23513 internal ESD diode continuous forward current level?

    do we have a recommend diode for VOUT to VEE?

    I will also support customer to identify the negative voltage waveform and help them to eliminate it.

    BR

    Emma

  • 0 in reply to Emma Wang
    TI__Genius 15856 points

    Hi Emma,

    That is concerning if the external diode is damaged. An internal integrated diode can absorb less power than a discrete diode.

    The integrated ESD diode current rating here is 20mA DC, but I have tested up to 60mA before damage. This of course translates to a much higher transient current. Please see my measured IV characteristic below. 

    BAT54 is usually my ESD diode of choice, but 30Vr might not be high enough voltage in this case. What are their supply rails?

    What is going on here? Do you have any Vout waveforms?  First we should figure out if the diode is failing due to overcurrent or overvoltage. If it's voltage, we might benefit from filtering the EOS with a parallel capacitor more than changing the diode. If overcurrent, we need to look at their high-voltage switching behavior and try to eliminate sources of resonance.

    Best regards,

    Sean