LOG200: The output oscillates

Yuta Nishie

Part Number: LOG200

Hi,

The following Application Note, page 14, Figure 7-1. I created a circuit referring to LOG200 Driving a Fully-Differential Input ADC. VS- is changed to -5V.

www.ti.com/.../sboa601.pdf

However, the output oscillates even though there is no input signal. Could you tell me the possible cause? The output oscillates even when the circuits after RFIL1 and RFIL2 are disconnected.

Please let me know if you need any information.

Best Regards,

Nishie

4 months ago

0 Taylor Allan 4 months ago

TI__Intellectual 1290 points

Hi Nishie-san,

Do you know the frequency/amplitude of the oscillations? Do you see any oscillations on the reference/power supply pins? I would make sure you added a 100nF decoupling cap between the negative power supply and ground if you haven't.

Usually I would suspect a capacitive loading issue, but the 1kOhm resistor should work as an isolation resistor for the output as it is based on an existing app note.

Could you also check if you have followed the layout guidelines in Section 7.4.1 in the LOG200 datasheet?

Best Regards,

Taylor Allan

0 Yuta Nishie 4 months ago in reply to Taylor Allan

Genius 5750 points

Hi Taylor-san,

Thank you for your support.

I will proceed to obtain the waveform. Please give me some time.

Best Regards,

Nishie

0 Taylor Allan 4 months ago in reply to Yuta Nishie

TI__Intellectual 1290 points

Hi Nishie-san,

Of course, I'm happy to help.

Best Regards,

Taylor Allan

0 Yuta Nishie 4 months ago in reply to Taylor Allan

Genius 5750 points

Hi Taylor-san,

Sorry for the late reply.

For some unknown reason, the LOG200 no longer oscillates on the customer's board. So please close this thread.

Best Regards,

Nishie

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LOG200: The output oscillates