TLC339: clamp current of the comparator

GEO FRANCIS

Part Number: TLC339

I am using TLC339 comparator in one of our circuit with the VCC=3.3V and GND. I have attached the schematic. The input is a square wave with frequency of 100Hz and amplitude is +/- 15V.

When the input is -15V the diode will be forward bias and the input of the ic will see the -700mV whether will this create any issue for the IC? as per the datasheet the input voltage max is -300mV. But the clamp current is +/- 3mA. as per the schematic we are not crossing the 3mA current.

Please let me know if you have any concerns??

over 7 years ago

0 Jian Zhang5 over 7 years ago

TI__Prodigy 600 points

The TLC339's built-in ESD diodes protect its input from out-of-range input values as long as the current is limited. In your case the maximum current is less than 700mV/1k=0.7mA which is within the acceptable range. So your circuit is good to go in terms of the input level.

0 GEO FRANCIS over 7 years ago in reply to Jian Zhang5

Prodigy 220 points

whether this input signal will effect any performance of comparator?

0 Jian Zhang5 over 7 years ago in reply to GEO FRANCIS

TI__Prodigy 600 points

In your case, the input related parameters such as input bias current, CMRR, etc. could be affected. Options to minimize the impact include:

1. adding a low forward bias schottky diode in parallel with the zener diode to reduce the worst case negative voltage
2. Increase resistor R353 from 1k to say10k or even 100k to limit the current

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TLC339: clamp current of the comparator