Tool/software:
Hi team,
I find that our HV amps such as OPA4171 has back-to-back diodes for input protection (OPA4991 doesn't have and achieve in another way), but I don't find similar design in our LV amps such as TLV9004. I want to understand why we have it for HV amp but not for LV amp? thanks.
Best regards,
Yang
Hi Yang,
Please see the following posts that contain information regarding the back to back diodes. You may find some of the discussion answers part of your question.
https://e2e.ti.com/blogs_/archives/b/thesignal/posts/op-amps-used-as-comparators-is-it-okay
Note that in one of the posts Bruce mentions "Most low voltage CMOS op amps do not have clamps. There is a special exception for auto-zero or chopper types that may have behaviors that look like clamps." You will find a post from Marek discussing parasitic back to back diodes in a low voltage device such as the OPA333.
I hope this information is useful. Let me know if I can be of further assistance.
Best Regards,
Chris Featherstone
Hi Yang,
I want to understand why we have it for HV amp but not for LV amp?
OPA4171 and OPA4991 use different input and ESD protection scheme for op amps, and it is not necessarily related to HV or LV application, see the thread below.
The CMOS op amps have back to back diode protection with following characteristics.
1. Input stage protection, which the differential input signal is clamped to +/-0.7V and protection the gate oxide of mosfet transistors from overvoltage stress
2. Typically it is implemented for precision or low voltage design. Many audio amplifiers use back to back input diode protection.
3. Rail to rail input stages have PMOS and NMOS differential pairs operating over different regions.
4. Prevent distortion from input overload, and it is typically simple, effective and low cost input protection.
For CMOS op maps without back to back diodes protection:
a. It uses different input clamp circuitry
b. Wider differential voltage tolerance such as Mux-friendly op amp in ADC application.
c, Use different ESD protection scheme and reply less on the differential clamps between inputs.
d. Lower leakage, high input impedance and lower input capacitance.
Below is the comparisons of two op amps. The selection of the op amp should tailor to an actual application.
If you have other questions, please let me know.
Best,
Raymond
