LHM6518 Low gain works abnormal. May damaged.

Yuanyu Tseng

Prodigy 60 points

Other Parts Discussed in Thread: LMH6518, ADC08D1000

Initial conditions the LMH6518 set to Low Gain mode.

The +IN of LMH6518 is connect with a DC(+2V) + Squared waveform(2Vp-p 100kHz).

The -IN of LMH6518 is connected with a DC(+2V).

The VCM is connected with 1.25V from ADC08D1000.

And, the bottom of squared waveform is calibrated to the center of ADC.

After 24 hours testing, the squared waveform will be adding an "DC offset" by the LMH6518 even cycling the power.

By the same testing method, it works normal(no dc offset) for High gain mode of LMH6518.

Obviously, the LMH6518 was damaged.

any suggestion? or workaround for this issue?

over 9 years ago

0 Loren Siebert 1 over 9 years ago

TI__Genius 13935 points

Hello Yuanyu,

It looks like you are using the LMH6518 with it's rated absolute maximum input voltage. Somethings that might help are:

1. Attenuate the singal with external resistors before the amplifier to lower the input voltage.

2. Use series resistors in the input path to limit input current to the amplifier input pins.

Regards,

Loren

0 Yuanyu Tseng over 9 years ago in reply to Loren Siebert 1

Prodigy 60 points

May the input voltage of +IN is over the rated absolute maximum input voltage.

I try to reduce the input voltage of +IN to DC(+2) + Squared waveform (1Vp-p 100kHz) the LMH6518 is damaged, too.

Regards,

0 Loren Siebert 1 over 9 years ago in reply to Yuanyu Tseng

TI__Genius 13935 points

Hello Yuanyu,

I think I need some additional information to help you. Would it be possible to put up a schematic of your test circuit as well as some screen shots of the DC offset?

Is this circuit fully DC coupled? How large is the DC offset?

Regards,

Loren

0 Yuanyu Tseng over 9 years ago in reply to Loren Siebert 1

Prodigy 60 points

Hi Loren,

it's fully DC coupled.

The symptom can be duplicated by FIG68 of this pdf .

http://www.ti.com/lit/ds/symlink/lmh6518.pdf

2.5V as input bias center.

The signal amplitude 1Vp(0v to 1V swing square wave)

the peak voltage apply on +IN is 3.5V(=2.5+1)

Low gain mode, it will damaged the device after applying this signal for 24 hours.

Regards,

0 Hooman Hashemi over 9 years ago in reply to Yuanyu Tseng

TI__Mastermind 22825 points

Hi Yuanyu,

We have done some bench testing but have not been able to see the offset shift that you've observed! You will be contacted directly to try and figure out the issue you are having.

Regards,

Hooman

0 Yuanyu Tseng over 9 years ago in reply to Hooman Hashemi

Prodigy 60 points

Hi Hooman,

In the fact, no one contact with us.

Regards,
YY

0 Hooman Hashemi over 9 years ago in reply to Yuanyu Tseng

TI__Mastermind 22825 points

Hi YY,
Your TI field representative will contact you directly to share the data we collected in-house in our unsuccessful attempt to create the offset voltage drift you have measured.

Regards,
Hooman

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LHM6518 Low gain works abnormal. May damaged.