LM6172: Input Protection Circuitry

Sadanori Kato

Part Number: LM6172
Other Parts Discussed in Thread: OPA1611, , OPA1612

Hi,

Could you please tell me whether the input terminals of LM6172 are protected from excessive differential voltage with back-to-back diodes like as the input protection circuitry on OPA1611 ?

Best regards,
Kato

over 6 years ago

0 Sima Jalaleddine over 6 years ago

TI__Mastermind 31465 points

Hello Kato-san,

We are looking into this, and will get back to you with an update soon. At first glance of the absolute differential input voltage of +/- 10V, we do not believe there are the back-to-back diodes for protection against excessive differential voltage.

Thank you,

Sima

0 Sadanori Kato over 6 years ago in reply to Sima Jalaleddine

Guru 36540 points

Hi Sima-san,

Thank you for your quick response.

The input resistance Rin with common-mode is as high as 40MΩ. On the other hand, the absolute maximum rating of input current is specified as +/- 10mA. So I think there are the back-to-back diodes.
I am looking forward to getting the detailed information from you ASAP.

Best regards,
Kato

0 Sadanori Kato over 6 years ago in reply to Sadanori Kato

Guru 36540 points

Hi Sima-san,

Sorry for rushing you but please let me know if you have any updates.

Best regards,
Kato

0 Sima Jalaleddine over 6 years ago in reply to Sadanori Kato

TI__Mastermind 31465 points

Hello Kato-San

I am sorry for the delay, we are still looking into this. I will update you by the end of this week.

Thank you,

Sima

0 Sadanori Kato over 6 years ago in reply to Sima Jalaleddine

Guru 36540 points

Hi Sima-san,

Thank you for your prompt reply.

I am looking forward to getting the information from you.

Best regards,
Kato

0 Sima Jalaleddine over 6 years ago in reply to Sadanori Kato

TI__Mastermind 31465 points

Hello Kato-san,

Sorry, I do not have a definite answer on this thread yet. I will try one more source, and will update you once I know.

Thank you,
Sima

0 Sadanori Kato over 6 years ago in reply to Sima Jalaleddine

Guru 36540 points

Hi Sima-san,

Thank you for following me.

I think that it can be judged by whether LM6172 damages by using LM6172 as a comparator. However, there is no LM6172 sample at hand.
Please let me know if you have any updates.

Best regards,
Kato

0 kai klaas69 over 6 years ago in reply to Sadanori Kato

Guru 140200 points

Hi Sadanori,

I agree with Sima. I don't think that there are back-to-back protection diodes between the inputs of LM6172. Zener diodes would have too much capacitance and would allow too high a heat dissipation with 10mA. A series circuit of many pn-junctions would cost too much die area and a single pn-junction with internal current limit resistors in series would create too much noise.

The maximum input current specification of +/-10mA in the "absolute maximum ratings" are related to the internal ESD protection diodes protecting the LM6172 against input voltages exceeding the supply voltages:

Kai

0 Sadanori Kato over 6 years ago in reply to kai klaas69

Guru 36540 points

Hi Kai-san,

Thank you for the information.

Have you actually used LM6172 as a comparator ?
There is mentioned in OPA1612 data sheet as well.

Best regards,
Kato

0 Sima Jalaleddine over 6 years ago in reply to Sadanori Kato

TI__Mastermind 31465 points

Hello Kato-san,

I have a definite answer now. Kai is correct; the maximum input current specification is related to the internal ESD protection diodes. There are no back-to-back diodes in the LM6172. The suggestion you provided in your previous response is correct as well. If this part was to be used as a comparator or in some open-loop configuration, the part will be damaged due to prolonged output saturation.

Thank you,

Sima

0 Sadanori Kato over 6 years ago in reply to Sima Jalaleddine

Guru 36540 points

Hi Sima-san and Kai-san,

Thank you for the information.

I understand.
By the way, Is it possibility for LM6172 to be damaged due to oscillation when using LM6172 as I/V converter without the isolated resistor Riso ?

Best regards,
Kato

0 kai klaas69 over 6 years ago in reply to Sadanori Kato

Guru 140200 points

Hi Sadanori,

yes, there is a risk for an oscillating OPAmp to be damaged.

Kai

0 kai klaas69 over 6 years ago in reply to kai klaas69

Guru 140200 points

Hi Sadanori again,

regarding your earlier question: I would not use a HF-OPAmp as a comparator. I would take a special comparator chip for this.

Kai

0 Sadanori Kato over 6 years ago in reply to kai klaas69

Guru 36540 points

Hi Kai-san,

Thank you for always helping.

I understand.

Best regards,
Kato

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LM6172: Input Protection Circuitry