Hi team,
My customer asks question how to select MOS FET for HVPACK+ especially in terms of VGS.
For BQ79731EVM, FQU2N100-D are used for HVPACK+, HV_FUSE+, etc for high voltage (400V) measurement, and Vgs would be 6V at maximum from resistor dividing ratio.
Could you check question in attached sheet related to adapting Power MOSFET?
Question_about_Power_MOSFET.xlsx
best regards,
Hi Nobuo,
Hope your day is well. I can't guarantee any values about the FQU2N100-D as its not our component, but I can still help.
Q1) Looking at the datasheet for the FQU2N100-D (https://www.onsemi.com/pdf/datasheet/fqu2n100-d.pdf), there is an Rds vs drain current graph. In general, Rds should increase as Vgs decreases, but I do not see any data in the FQU2N100-D datasheet on what Rds is below Vgs = 10V so I cannot claim how much it will change if at all:
Assuming the drain current stays at 200uA, the Rds should be 7.1 ohms as stated in the "ON CHARACTERISTICS":
The second important graph for Rds is how it varies over tempurature:
For the temperature and current conditions your application will be operating under, multiply the normalized value by the Rds value found on the previous graph (7.1 ohms) to get the estimated Rds value.
Q2) If you are referring to the 2Mohm resistor between the 400V and the drain voltage as the resistor divider ratio, you will need to double the resistance for 800V to sustain 200uA. If you still want each resistor to have the same power dissipation as before, then use use 8x 500kohms instead of 4x. Hope this helps! if you have any additional questions or follow ups, repost in the internal forum as this is a public forum.
Best,
David Ray
