BUF602: BUF602 as capacitive gate load driver?

Doug Widney

Part Number: BUF602
Other Parts Discussed in Thread: BUF634, TINA-TI

I'm looking at using a BUF602 in a closed servo loop, driving a single mosfet with gate capacitance in the 400pF-800pF range. This is in an analog pulse application. Mosfet is common source mode and will be subject to Miller effect multiplication before/during mosfet turn on, but not appreciably during the pulse on time. tLoop BW will be in the 1-2MHz range. BUF602 will be driven by an OP2727 output. Single 9V rail.

Anybody have a reassurance that the BUF602 will be OK with this? It has a closed loop of its own internally. There isn't specific mention of capacitive gate drive in the datasheet header. However, the datasheet does show one graph of capacitive load up to 1nF versus "Rs", which I take to be a series resistor placed in the BUF602 output. It shows about 1 ohm at 1nF--fast but startlingly low resistance.

I could use BUF634 (/A), open loop, no such worries--but it would need a negative rail which is awkward in this system.

Anybody done this or have a take on it?

rgds.,

Doug Widney

Doug Widney EnerDesign

Corte Madera CA

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Doug,

I would run a phase stability analysis in TINA-TI. There's a BUF602 TINA-TI reference design which you could use as a start. You will find it here:

www.ti.com/.../toolssoftware

See also the TI's stability training videos:

training.ti.com/ti-precision-labs-op-amps-stability-3

Kai

0 Michael Steffes over 5 years ago in reply to kai klaas69

Guru 48395 points

Hey Doug,

Yes, the BUF602 is internally closed loop - you cannot run the typical LG phase margin tests as you would have to go inside the netlist to open the loop. The required external R to improve phase margin will go down with cap load. The model should help you find the right R value into your cap load. From the response peaking at the output pin (before the isolating R) you can estimate phase margin using the plots at the beginning of this article.

www.planetanalog.com/author.asp

0 Alec Saebeler over 5 years ago

TI__Genius 16401 points

Hi Doug,

Are you still looking for more information on the use of a BUF602 as a capacitive gate load driver?

I saw Michael and Kai both had good comments, I would concur to start with those approaches and references. I wanted to follow up and see if you were able to find the information/data for which you had been looking, and touch base if you still had questions.

Thanks,

Alec

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BUF602: BUF602 as capacitive gate load driver?