LM2901B-Q1: The work condition of LM2901

Zhang Yuhua

Prodigy 100 points

Part Number: LM2901B-Q1
Other Parts Discussed in Thread: LM2901, TLV1805-Q1, TLV1704-Q1, , LM339

Hi Experts:

It set VCC of LM2901 is 9~16V, IN+ =VCC/2 :

When IN- is equal to VCC-0.7V，is the out`pin output high?

When IN- is equal to 0V，is the out`pin output low?

10 months ago

0 Clemens Ladisch 10 months ago

Guru 259720 points

No; it's the opposite. The output is high when the non-inverting input IN+ is higher than the inverting input IN−. In other words, the output follows the signal at IN+, or inverts the signal at IN−.

Please note that V_CC − 0.7 V is outside the valid input voltage range. The LM2901B-Q1 can still work when only one input has an invalid voltage, but the electrical characteristics (especially propagation delay) are no longer guaranteed. Better use a comparator with rail-to-rail inputs like the TLV1704-Q1 or TLV1805-Q1.

0 Paul Grohe 10 months ago

TI__Guru 51546 points

Hello Zhang,

Please see sections 2.5, 2.7 and 2.8 of the LM339 family application note:

Application Design Guidelines for LM339, LM393, TL331 Family Comparators

As Clemens mentioned, you would be relying on an expected result, but not guaranteed. TI will always recommend staying within the recommended input specifications (Vcc-2V).

0 Zhang Yuhua 10 months ago in reply to Paul Grohe

Prodigy 100 points

Hi Paul：

We haved viewed the documents，we corrected the designing as below：

1、VCC=9V,when 1IN-=3V, 1IN+=5.6V ，Output is High； when 1IN-=3V, 1IN+=0.1V output islow.

2、VCC=16V, when 1IN-=5.2V, 1IN+=10V ，Output is High；1IN-=3V, 1IN+=0.1V output is low.

Can we get the result what we want？ Please help us to review it

+1 Clemens Ladisch 10 months ago in reply to Zhang Yuhua

Guru 259720 points

Yes; the circuit will work with these values.

In the image, the GND pin and the inputs of the unused comparators are floating. I guess this will not be the case in the real circuit.

0 Zhang Yuhua 10 months ago in reply to Clemens Ladisch

Prodigy 100 points

Hi Clemens:

I get it. Thank you very much

+1 Paul Grohe 10 months ago in reply to Zhang Yuhua

TI__Guru 51546 points

Agreed!

Section 5 of the appnote shows what to do with unused channels.

0 Zhang Yuhua 10 months ago in reply to Paul Grohe

Prodigy 100 points

Hi Paul

I get it. Thank you very much

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LM2901B-Q1: The work condition of LM2901