[ADuM7223]How to design High-Side voltage when MOSFET gated 200V?

Hello,

I would like to know about H-Bridge driver circuit with using ADuM7223.

According to

https://ez.analog.com/message/129916#129916

I understood VDDA and VDDB should be separate supply, but I cannot find any reference circuit.

I also refer to

http://www.analog.com/static/imported-files/tech_articles/Inside_iCoupler_Technology_Driving_an_H_Bridge.pdf

Is there any information how to VDDA supply when Vbridge voltage max 200V? (This apps note Vbridge is about 16V.)

Actually, one customer had designed with following above pdf Fig.1 with using ADuM7223 instead of ADuM7234 and Vbridge is 200V.

But High-side voltage output is only about 5V instead of 200V.

Thank you for your help in advance.

Best regards,

Sofy

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  • 0
    •  Analog Employees 
    on Oct 18, 2017 11:44 PM

    Hello,

    Yes, the Vgs voltage relative to the source node can be run negative since GNDa is floating. This is one of the advantages of digitally isolated gate drivers as compared to high-voltage level shifters. The VDDA/VOA/GNDA pins are on one silicon die, and the VDDB/VOB/GNDB pins are on a totally separate silicon die. If you wanted, the B region could be used as a high side, as there is no differentiation between the A and B with respect to what needs to be at a lower potential.

    The ADuM7234 has a recommended VDDA/B range that goes to 18 V, so +15, -5 is too much for it (since this is 20 V total). Parts that will work with this range are the ADuM4120, ADuM4121, ADuM4135, and ADuM4136.

    One nifty way to obtain the negative rail is to supply a 20 V source for the gate driver secondary side, but split it into two effective rails using a Zener diode. Here is a a figure to help the discussion:

    We can see here that the VDD to GND voltage is V1 + V2. The Q1 gate to source (Vgs) will swing from V1 to negative V2. From the gate driver's perspective, it only sees a unipolar supply (V1 +V2), but the gate voltage delivered to Q1 sees a bipolar supply!

    Here is the same circuit shown with one possible zener diode configuration:

    Dz in this example would be a 15 V Zener. Rz should be chosen such that there is enough current to sustain the switching gate drive current. V3 in this example would be 20 V to support the +15 V, -5 V target you mention. You could also swap the placement of Dz and Rz, using a 5 V Zener to create the negative rail as well. The main cost of this implementation is added quiescent current draw on the isolated power supply.

    For SiC, I would recommend the ADuM4121. It has an integrated Miller clamp, and a wide output voltage range that is compliant with most SiC requirements. Additionally, its CMTI rating is very high, at 150 kV/µs, which is sufficient for almost all SiC devices on the market today. My second choice would be the ADuM4120. It is a 6 pin gate driver, and has the same high CMTI rating as the ADuM4121, but no Miller clamp. Since one of the main reasons to drive a gate negative is to avoid accidental Miller induced turn on, using a part without a Miller clamp is a viable option. Single channel devices allow for easier layout, which is very important for the wide bandgap devices today.

    One thing to note is that if you are making a bipolar operation from a unipolar supply, bootstrapping becomes interesting to say the least. Since the lowside switch is used to ground the highside, we only really get to charge the positive voltage of the highside. Due to the complexity of describing how to setup a bipolar bootstrap, right now I'd recommend using an isolated DC/DC converter for the +20 V supply. That also frees you up from duty cycle and frequency minimums forced upon a bootstrap design.

    RSchnell

Reply
  • 0
    •  Analog Employees 
    on Oct 18, 2017 11:44 PM

    Hello,

    Yes, the Vgs voltage relative to the source node can be run negative since GNDa is floating. This is one of the advantages of digitally isolated gate drivers as compared to high-voltage level shifters. The VDDA/VOA/GNDA pins are on one silicon die, and the VDDB/VOB/GNDB pins are on a totally separate silicon die. If you wanted, the B region could be used as a high side, as there is no differentiation between the A and B with respect to what needs to be at a lower potential.

    The ADuM7234 has a recommended VDDA/B range that goes to 18 V, so +15, -5 is too much for it (since this is 20 V total). Parts that will work with this range are the ADuM4120, ADuM4121, ADuM4135, and ADuM4136.

    One nifty way to obtain the negative rail is to supply a 20 V source for the gate driver secondary side, but split it into two effective rails using a Zener diode. Here is a a figure to help the discussion:

    We can see here that the VDD to GND voltage is V1 + V2. The Q1 gate to source (Vgs) will swing from V1 to negative V2. From the gate driver's perspective, it only sees a unipolar supply (V1 +V2), but the gate voltage delivered to Q1 sees a bipolar supply!

    Here is the same circuit shown with one possible zener diode configuration:

    Dz in this example would be a 15 V Zener. Rz should be chosen such that there is enough current to sustain the switching gate drive current. V3 in this example would be 20 V to support the +15 V, -5 V target you mention. You could also swap the placement of Dz and Rz, using a 5 V Zener to create the negative rail as well. The main cost of this implementation is added quiescent current draw on the isolated power supply.

    For SiC, I would recommend the ADuM4121. It has an integrated Miller clamp, and a wide output voltage range that is compliant with most SiC requirements. Additionally, its CMTI rating is very high, at 150 kV/µs, which is sufficient for almost all SiC devices on the market today. My second choice would be the ADuM4120. It is a 6 pin gate driver, and has the same high CMTI rating as the ADuM4121, but no Miller clamp. Since one of the main reasons to drive a gate negative is to avoid accidental Miller induced turn on, using a part without a Miller clamp is a viable option. Single channel devices allow for easier layout, which is very important for the wide bandgap devices today.

    One thing to note is that if you are making a bipolar operation from a unipolar supply, bootstrapping becomes interesting to say the least. Since the lowside switch is used to ground the highside, we only really get to charge the positive voltage of the highside. Due to the complexity of describing how to setup a bipolar bootstrap, right now I'd recommend using an isolated DC/DC converter for the +20 V supply. That also frees you up from duty cycle and frequency minimums forced upon a bootstrap design.

    RSchnell

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