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# OPA356-Q1: Cable driver

Part Number: OPA356-Q1

Hi

Our customer are considering that this device can drive coaxial cable at the following input conditions.

- Fin=125MHz,

- Vin_pp=1Vpp @Vdd=3.3V

- Vcm=+1.5V (+/-0.5V=1Vpp)

If it is not possible to use this device at the above condition for cable driver, please give us some other device that you recommend.

(We are considering OPA355 and OPA354 as well.)

Regards,

Koji Hamamoto

• Hi Koji,

I would also try the LMH6611 for its higher bandwidth.

Best regards,

Sean
• In reply to Sean Cashin:

Hi

I would like a automotive device. Are there any other device what you recommend for this requirements?

- Fin=125MHz,

- Vin_pp=1Vpp @Vdd=3.3V

- Vcm=+1.5V (+/-0.5V=1Vpp)

Regards,
Koji Hamamoto

Hi Sean,

I have one more concerns.
Our customer would like to use this device for a coaxial cable driver. Is that possible?
Because the output current for coaxial cable (50ohm) is certain current.

Also common-mode range concerns.

Regards,
Koji Hamamoto

Hi Koji,

Unfortunately, we don't seem to have any automotive rated parts that can buffer a 125MHz 1Vpp signal. The parts you have found are the closest we currently have.

Best regards,

Sean
• In reply to Sean Cashin:

Hi Sean,

For those devices what we found, do you think the slew rate is enough at the following condition?

- Fsig = 125MHz (Max) : Sin wave

- Vout_pp = 1.5Vpp (Max)

Because OPA355 and OPA356 has ability 300V/us of slew rate. However for the above condition, I think the slew rate should be more than 600V/us. What do you think?

Is my understanding correct? 　(dt/dV = PI * Fsig * Vp = PI * 125[MHz] * 1.5Vpp = 589V/us)

Regards,

Koji Hamamoto

Hi Koji,

Yes, your understanding is correct. The OPA355 and 356 will be slew rate limited under this condition. The slew rate is what causes the amplifier's large signal bandwidth to be less than its small signal bandwidth. To determine whether or not an amplifier can drive a coaxial cable at a desired signal voltage, just check to see how well it can drive a load of Rsig+Zcharacteristic, or in this case 50+50=100ohms. This is limited by the amplifier's linear current output rating and the signal voltage.

Best regards,

Sean

• Hi

you can use LM 6181

i have tested it for 20meter long coaxial cable and result are reliable with great accuracy.
• In reply to hasmukh kabariya:

Hi Hasmukh,

LM6181 what you recommended will be EOL. And THS3120 is replaceable device is not automotive device.
Is there any device what you recommend?

Regards,
Koji Hamamoto

Hi Sean,

I understood. And I confirmed the behavior at the 50+50 ohm capability with TINA-TI.

It looks the output is little bit smaller than I expected. However as you mentioned I think it is caused by slew rate.

Is there any other recommended device?

Regards,

Koji Hamamoto