LM74700-Q1: enable input high threshold range

Thomas Bewley

Part Number: LM74700-Q1

The LM74700-Q1 datasheet lists its "enable input high threshold" as 1.06V (min), 2V (typ), 2.6V (max), which is a curiously (and, for me, inconveniently) big range (well over a factor of 2 from Vmin to Vmax!). I have an application where I will, for a short while (when starting up the MOSFET), be driving this enable pin with a 3V ML1220 rechargeable coin cell, which actually spends most of its operational life at 2.5V +/- 0.1V (see page 4 of https://media.digikey.com/pdf/Data%20Sheets/Panasonic%20Inustrial/ML_Serie.pdf). Let's say that I can guarantee the ML1220 will be at least half-charged, so I can provide at least 2.4V to the enable pin (but maybe not 2.6V).

Will the LM74700-Q1 possibly not turn on if I only provide 2.4V to it? Does the 1.06V (min), 2V (typ), 2.6V (max) range represent part-to-part variation? I can't imagine your ICs would vary that much. I imagine that the enable pin is connected to the gate of a transistor at where it comes onto the LM74700-Q1. I suppose I could pipe my enable signal (powered by the ML1220, at 2.4V or higher) into another transistor, and use the output of that to drive the enable input of the LM74700-Q1, but that really seems redundant.

So, my question: will 2.4V or higher provided on the enable pin of a LM74700-Q1 reliably enable the MOSFET to which it is connected?

Thanks in advance for the clarification,

Tom

over 5 years ago

0 Thomas Bewley over 5 years ago

Expert 1030 points

PS - It might be useful information to point out that V_IN in my application will be in the range 5V to 28V. [If you care, the application that requires the LM74700-Q1 to be enabled for a short while by an ML1220 coin cell is described further here: https://community.st.com/s/question/0D53W000007Z0soSAC/using-an-stm-rtcout-line-for-enablingdisabling-the-main-power-mosfet-on-a-board-which-idles-in-vbat-mode-when-not-in-use .]

PPS - I found a primer on TTL logic here https://learn.sparkfun.com/tutorials/logic-levels/all which stated "The minimum input HIGH voltage (VIH) is 2 V, or basically any voltage that is at least 2 V will be read in as a logic 1 (HIGH) to a TTL device." If the LM74700-Q1 behaves this way on its ENABLE pin, I'm good. :)

0 Karikalan Selvaraj over 5 years ago in reply to Thomas Bewley

TI__Genius 16305 points

Hello Thomas,

2.6V is the maximum threshold for EN pin of LM74700-Q1.

For your usage, we recommend to pull up the EN pin to ANODE so that it is default enabled and using a pulldown (MOSFET or BJT) controlled by 2.4V coin cell could help?

Let us know if this works?

Regards,

Kari.

0 Thomas Bewley over 5 years ago in reply to Karikalan Selvaraj

Expert 1030 points

Hmm. In the interest of minimizing current drain while in OFF mode, I might simply switch from an ML1220 to a (more expensive) VL1220, which would reliably provide at least 2.6V.

I am still wondering about the huge range 1.06V (min), 2V (typ), 2.6V (max), though. Does this indicate part-to-part variation, or is this very large range a function of, say, what voltage is used for V_IN?

0 Karikalan Selvaraj over 5 years ago in reply to Thomas Bewley

TI__Genius 16305 points

The variation is due to temperature variation and part-part variation as well.

It doesn't depend a lot on VIN, mainly the temperature and production (part-part) variation.

Regards,

Kari.

0 Thomas Bewley over 5 years ago in reply to Karikalan Selvaraj

Expert 1030 points

Ok, I understand. Thanks. To summarize: I really do need to hold that pin at 2.6V or higher in order to reliably turn on the MOSFET. Will do. (A vl1220 coin cell will get me there, where an ml1220 generally might not.)

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LM74700-Q1: enable input high threshold range