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I made a simple window comparator like this:enter image description here

I'm using LM293, R1 and R2 sets a Vlow and Vhigh threshold, when input is inside Vlow and Vhigh, both leds are off, when input is above or below, one of the leds turns on. This is working ok.

To reduce consumption i changed LM293 by TLV3402, but window comparator does not work anymore. When input is outside window, leds don't turn on.

Both ICs have the same pinout (i use the same circuit, just replace one IC by the other), why TLV3402 does not work? It is not a fault one, i tested with a second one, the same result.

Are these IC the same, or am i missing something?

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  • \$\begingroup\$ You've wired it incorrectly. \$\endgroup\$ – Andy aka May 9 at 12:01
  • \$\begingroup\$ Can you please clarify? what wires are incorrect? \$\endgroup\$ – Geologic May 9 at 13:42
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    \$\begingroup\$ You need to show the precise circuit that you implemented in order to determine this. Showing an approximation to your real circuit gets nobody anywhere in trying to help you. \$\endgroup\$ – Andy aka May 9 at 13:45
  • \$\begingroup\$ Updated question with schematic \$\endgroup\$ – Geologic May 9 at 16:10
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Are these IC the same?
NO

Don't expect more than 5mA from that nanoAmp OA. 10mA is ABS MAX.

So just increase R to the appropriate value.

The answers are usually in the datasheet.

Fig 3,4,5 Indicate this IC is not intended for driving LEDs. Using the slope of Vol/Iol as the driver impedance, I compute;

Vcc vs Ro

2.7 V ... 2.7 kΩ
5.0 V ... 1.6 kΩ
15. V ... 1 kΩ

When in doubt verify all pin voltages, especially Vout.

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  • \$\begingroup\$ I'm using R=500K and Rpullup=1M, it consumes less than 1mA \$\endgroup\$ – Geologic May 9 at 13:41
  • \$\begingroup\$ what Rs to drive LEDS?? \$\endgroup\$ – Sunnyskyguy EE75 May 9 at 14:07
  • \$\begingroup\$ i used 1K with LED, but tested with 10k, didn't result \$\endgroup\$ – Geologic May 9 at 16:11
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Well, i discover the problem, the TLV3402 IC package has thinner pins than the LM293, so one of the pins were not making contact. Now it is working ok, even with LEDS.

Thanks Sunnyskyguy for pointing me the output current limit for this IC.

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