A couple of questions for AD8336

Hi KAOS,

Thank you for your interest in AD8336. I have verified your questions from the Applications Engineer responsible of this part. Please see the answers below:

1)

What is the input-impedance of VGAI pin?

I can see the 1.28kohms on your datasheet page-20.

Does this means the impedamce,correct?

Yes, you are correct. The input impedance of the VGAI pin of AD8336 is 1.28kohms as shown on page 20.

2)

Why is LPF(low pass filter) put at AN-934 page-4?

(closing output pin, 100ohm and 4.7nF)

I think that this means 36kHz cut off frequency.

eg) If I need the 20kHz cut off frequency, can I put the 20kHz LPF there?

The LPF is used to limit out of band noise. The cutoff frequency is actually ~338.6kHz. The cutoff frequency was determined as such to accommodate the maximum expected frequency of 20kHz. Usually, the cutoff frequency of the filter is around 10 times greater than the maximum expected signal frequency. Yes, you can put a 20kHz LPF but your maximum signal frequency should be around 2kHz.

3)

If I dont use the internal preamp on AD8336, how can I deal the opened 3 pins INPP, INPN, and PRAO?

In general, connect INPP to GND, and short INPN to PRAO, correct? It is similar as voltage follower circuit.

You are correct. Unused op amps are configured in a voltage follower configuration and connect the input to within the IVR of the amplifier. For a dual supply, connecting the input to ground is a common practice. This will minimize unwanted output from the amplifier to affect the rest of the circuit. .

I hope this helps.

Best regards,

Neil