BUF634A: Capacitive load and TINA TI SPICE MODEL

Info WAPTEL

Part Number: BUF634A
Other Parts Discussed in Thread: LMH6321, , BUF634, TINA-TI

Hello,

We have compared the performance of two IC buffers: BUF634A and LMH6321 to drive a large capacitive load (e.g., 1nF) using a very simple circuit. Simulation results based on the free Tina TI software indicate that LMH6321 shows a better transient response than BUF634A. Is the free TINA-TI using the right BUF634 spice model? From older posts, it seems that the model implements the wide-bandwidth mode.

Thanks,

Enrique

PS: Test circuit consists of the source (square wave) directly connected to the buffer. The ouput of the buffer is connected to the capacitive load.

over 3 years ago

+1 Sam Burnett over 3 years ago

TI__Expert 3620 points

Hi Enrique,

Make sure you have the model for the BUF634A. The old BUF634 model from 1995 probably still shows up in the buffer list of TINA macro-models, but the new model for the BUF634A is available on the product page BUF634A data sheet, product information and support | TI.com

Best,

Sam

0 Info WAPTEL over 3 years ago in reply to Sam Burnett

Prodigy 30 points

Thank you very much. Yes, this is the case. We have added the new model, which seems to work despite several warnings ("...Pin 3 of Current-Ctld. Switch ... is floating (This node will be grounded)").

Do you recommend to use the BUF634A in a composite amplifier arrangement for a high frequency application driving a large capacitive load? We have observed some ringing at the output of the first high-frequency op. amplifier (from simulation results). In the case of cascaded amplifiers, signals seem more stable for both amplifiers.

And the last question, since internal circuitry is limiting output current to approximately 350mA, can practical slew rate be affected by this parameter?

Regards,

Enrique

0 Sam Burnett over 3 years ago in reply to Info WAPTEL

TI__Expert 3620 points

Hi Enrique,

350mA is the approximate short circuit limit. Are you designing for a purely capacitive load? The appropriateness of a composite loop will depend on your application. Could you share a schematic?

Best,

Sam

0 kai klaas69 over 3 years ago in reply to Info WAPTEL

Guru 140200 points

Hi Enrique,

this thread may interest you:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1070070/buf634a-design-review-request-amplifier-driving-dc-voltage-onto-twisted-pair

Up to now we don't know the frequency range of your application. So please give more details.

Kai

0 Info WAPTEL over 3 years ago in reply to Sam Burnett

Prodigy 30 points

Thank you, Sam. It is not a purely capacitive load. The series resistance is small, and we should not add a resistor with a high value to avoid problems with the frequency response. Note that the peak current may reach Vload/Rseries (Cload is initially at 0V). This value will be eventually higher than 350mA at the beginning of the transient.

Best,

Enrique

0 Info WAPTEL over 3 years ago in reply to kai klaas69

Prodigy 30 points

Thank you, Kai. I will have a look at this thread. The frequency range covers from DC to about 10MHz.

Regards,

Enrique

0 Sam Burnett over 3 years ago in reply to Info WAPTEL

TI__Expert 3620 points

Would you like some assistance with the analysis? I can reach out to the design team regarding the slew behavior at short condition but more detail regarding the desired performance specs would be helpful.

Best,
Sam

0 Info WAPTEL over 3 years ago in reply to Sam Burnett

Prodigy 30 points

Thank you very much, Sam. I think we can handle the design with the current support.

Best regards,

Enrique

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BUF634A: Capacitive load and TINA TI SPICE MODEL