DRV2700EVM-HV500: DRV2700EVM-HV500 mosfet selection

Lesdey

Hello,

In the DRV2700EVM-HV500 you have choosen the mosfet BSS127 H6327XTSA2, could you please suggest to me an appropriate mosfet for a 800V application (I_out= 10mA).

Thank you for your support.

25 days ago

0 Ivan Salazar 25 days ago

TI__Guru** 113445 points

Hi,

Our team will take a look at your questions and get back with further comments this week after the holiday on Monday.

Best regards,
-Ivan Salazar
Applications Engineer

0 Lesdey 24 days ago in reply to Ivan Salazar

Prodigy 40 points

Hi,

Yes thank you. Could you please also explain to me how you did the calculation of Rd drain res and Rs source res (in the EVM is Rd=R27+R22 and Rs= R4)

Thank you for your support.

0 Hailong Chen 23 days ago in reply to Lesdey

TI__Expert 5280 points

Lesdey,

Usually we don't recommend other parties' components, but I do some quick search and some examples can be IXYS IXTA08N100D2 or STMicroelectronics STB10N95K3.

The source resistor Rs sets the current for the transistor that interacts with feedback pin. For a 3.3V or 5V input, a value of 2kohm to 10 kohm is common. You can keep the similar value to the EVM.

The drain resistors Rd limit the current through the MOSFET and define the gain of the modulation on the feedback pin. For 800V, you must increase these values relative to the 500V EVM to keep the current roughly the same. Increase value by ~60% vs 500V design.Ensure your resistors Rd are rated for the high voltage (800V). Standard 0805 resistors often only have a 150V-200V rating; you may need to use multiple resistors in series or specific high-voltage rated components.

0 Lesdey 23 days ago in reply to Hailong Chen

Prodigy 40 points

Thank you for your answer.
From my side I used IPN95R3K7P7ATMA1 with the appropriate feedback net resistor calculation for 800 V, but my circuit couldn't exceed 600V, is it normal ?

0 Hailong Chen 23 days ago in reply to Lesdey

TI__Expert 5280 points

It is normal for your circuit to be limited to a lower output voltage (600V instead of 800V), likely due to the voltage ratings of other components in the feedback or output stage, not the primary MOSFET itself. The IPN95R3K7P7ATMA1 MOSFET has a Drain-Source Voltage (Vdss) rating of 950V, so it is capable of handling an 800V output.

The limitation likely comes from other components in the feedback or rectification path:

Output Diode Voltage Rating: The secondary rectifier diode (labeled D2/RFUH25TB3S in the image context, though not clearly visible in the schematic) needs to handle a reverse voltage greater than the final output voltage (800V in your design). If this diode is only rated for, for example, 600V or 350V, it will break down and clamp the output voltage.
Feedback Circuit Component Limits: The operational amplifier (OPA2376AIYZDR) is only rated for a maximum supply voltage of 5.5V. The high-voltage divider resistors connecting to it must be carefully selected not only for the correct ratio but also for their individual maximum working voltage ratings. Standard small surface-mount (SMD) resistors often have very low maximum voltage ratings (e.g., 50V to 100V per component) which can easily be exceeded in high-voltage designs, causing them to fail or behave non-linearly.
Transformer Saturation/Design: Flyback converters store energy in the transformer core, and the power transfer is limited by the core's saturation and physical size. If the transformer wasn't designed to handle the required power/energy transfer for a full 800V output under your specific load conditions, it could saturate and limit the voltage.

To reach 800V, you should verify the maximum voltage rating of your output diode and the individual working voltage ratings of all resistors in your feedback network, replacing any components that are not rated for the higher voltages they encounter.

0 Lesdey 9 days ago in reply to Hailong Chen

Prodigy 40 points

Hello,

I tried to change the diode but the output voltage is still the same, I observed that SW voltage can’t exceed 50V even I changed feedback net resistors !

Do you have already a reference design for 800V or 1000V output ?

Thank you very much for your support.

0 Hailong Chen 8 days ago in reply to Lesdey

TI__Expert 5280 points

Lesdey, we don't have a reference design for 800V or 1000V output unfortunately.

0 Lesdey 8 days ago in reply to Hailong Chen

Prodigy 40 points

So what is the next step to verify if you could help me please !

thank you for your support.

0 Hailong Chen 8 days ago in reply to Lesdey

TI__Expert 5280 points

Please refer to the following two threads and see if they can help: e2e1, e2e2

0 Lesdey 2 days ago in reply to Hailong Chen

Prodigy 40 points

Hello, following different threads, I was able to reach 800 V, but only very briefly. As you can see in the image, Vout (pink) reaches 800 V only at the beginning, then it drops to 600–500 V. Similarly, Vfb (blue) is 1.3 V at the beginning, but it decreases afterward, and the driver cannot provide more energy to bring it back to 1.3 V (as I understand it).

I already tried changing Rext to 7.5 kΩ, and I also tried tying the GAIN1 and GAIN2 pins to logic 1 instead of 0 (GND).