UCC28700: DRV Pin Behavior

Michael Black2

Part Number: UCC28700

Hello,

I am trying to understand the behavior of the DRV pin for the UCC28700 flyback controller. The data sheet says the DRV pin is self-limited in both the amount of voltage it can supply and the amount of current it can supply. Does that mean it will attempt to operate at either the maximum voltage (14V), or the maximum current (25mA) at all times, and then self limit accordingly?

Perhaps the following example will help:

When the DRV pin goes high, what is the voltage, and how much current is being supplied?

Best,

over 3 years ago

0 Benjamin Lough over 3 years ago

TI__Mastermind 26225 points

Hi Michael,

The voltage can be as high as 14V (this is when the clamp turns on) or it will follow VDD if VDD is less than the 14V clamp. The sourcing current is limited to 25mA. The moment, the gate turns on, the pin will souce 25mA. This current charges up the Cgs of the mosfet. Once the gate voltage has reached 14V (assuming VDD is >14V) then current current out of the DRV pin will decrease. The DRV pin will limit the max sourcing current and the max voltage on the pin.

Best Regards,

Ben Lough

0 Michael Black2 over 3 years ago in reply to Benjamin Lough

Intellectual 340 points

So if I am understanding correctly,

without the current-limiting feature, we would otherwise see a huge current spike while the Cgs charged to 14V?

0 Benjamin Lough over 3 years ago in reply to Michael Black2

TI__Mastermind 26225 points

Hi Michael,

The spike would be limited by the internal impedance but yes, the current would be much higher without the current limiting feature.

Best Regards,

Ben Lough

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UCC28700: DRV Pin Behavior