Reverse diode current problem

[Md Mubdiul Hasan]

Hello there,

Take a look the schematic, I have observed this circuit in maximum and minimum temperature, the problems are

The gate of Q3 will be turned on at maximum temperature, while MAIN_PWR_EN is 0(disable).
1. D7 shows reverse diode current.
2. Q10 is also malfunctioning.

       
According to datasheet, torexsemi.com/file/xbs053v13r/XBS053V13R.pdf, the reverse current at 20V reverse volatge is 100u A. We are expecting a unidirectional current path towards R41 and R68 junction. Somehow in this circuit, current is producing,,,,

       
The parameters from datasheet of Q3 (onsemi.com/pub/Collateral/NTR2101P-D.PDF) says, if you calculate the gate current,Ig = Qg/(td(on)+tr); (Total Gate Charge) / (Turn-on delay time + rise time of MOSFET) it will about 0.37 A. (at VGS = ?4.5 V, VDD = ?4.0 V, ID = ?1.2 A, RG = 6.0 ohm) Reverse leakage might be temperature dependent, if you can see the circuit, a voltage difference between VIN(4.2v) and V_3V3 if Q3 is turned on that could make reverse path for diode conduction.

[danadak]

Downsides of schottky diodes are precisely what you observe,
high reverse leakage.

You might look around for a better part, 100 uA does seem a tad high.


Regards, Dana.

[RobK_NL]

I agree with Dana that that 100µA spec is pretty high. And that's at 25°C!

By comparison, the RB168LAM-30 (https://www.digikey.nl/product-detail/en/rohm-semiconductor/RB168LAM-30TR/RB168LAM-30CT-ND/7243343) is spec'd for 0.6µA max at 30V Vr.

[Md Mubdiul Hasan]

Downsides of schottky diodes are precisely what you observe,
high reverse leakage.

Do you mean downside diode D7?

You might look around for a better part, 100 uA does seem a tad high.

Can you compare my calculated gate current in actual case?

[Md Mubdiul Hasan]

By comparison, the RB168LAM-30 (https://www.digikey.nl/product-detail/en/rohm-semiconductor/RB168LAM-30TR/RB168LAM-30CT-ND/7243343) is spec'd for 0.6µA max at 30V Vr.

My company wish to replace, http://www.mouser.com/ds/2/348/rb520s-30-209876.pdf and I wanna do heat chamber test  again.
Do you agree with this part?

[danadak]

Yes on question D7, it is D7 being discussed.

Your Mouser replacement shows no high temp leakage performance.
You could contact vendor and ask for characterization data at high
temp.

I would sim this design to get at peak gate drive current. You could
use LTCspice, Tina TI spice, many vendors have simulators that would
handle this.

http://www.ti.com/lit/ml/slua618/slua618.pdf

https://www.semikron.com/dl/service-support/downloads/download/semikron-application-note-igbt-driver-calculation-en-2007-10-31-rev-00/

https://www.infineon.com/dgdl/an-944.pdf?fileId=5546d462533600a40153559eb9841190



Regards,. Dana.

[Md Mubdiul Hasan]

Thank you sir Danadak,

Your Mouser replacement shows no high temp leakage performance.
You could contact vendor and ask for characterization data at high
temp.

I will talk to them, but already the circuit is ready for production repair department.
I think, the suitable diode what RobK_NL has said is OK.

I would sim this design to get at peak gate drive current. You could
use LTCspice, Tina TI spice, many vendors have simulators that would
handle this.

Well said, I have been used those tool.
But, if you see the circuit we need to generate some shots of signal like MAIN_PWR_EN, PWR_HOLD, PWR_IND signal.
As this device is OS related firmware, we can just make signal conditioning  by the circuit.

Can you suggest which tool I need to apply here?
Any OR, AND, NOR, gate signal?