Voltage Comparator with 3.3V Internal Ref?

Other Hardware General Electronics
1

Hi there,

I'm looking for a voltage comparator (either open drain or push-pull output) that has an internal 3.3V voltage reference (a fixed "IN-" pin). Basically, if the voltage on IN+ is below 3.3V the chip outputs LOW, or if IN+ is above 3.3V it outputs HIGH (or high impedance state for open drain, either one works for me).

So basically the chip would have a total of four pins: VCC, GND, V+, and OUT.

I can't seem to find a voltage comparator like this. If there's nothing like this, I would have to use a separate 3.3V voltage reference IC. I am avoiding using a zener diode because I would have to use a pullup resistor, and this draws residual current, and the zener diode voltage may not be accurate. Any thoughts?

2

I can't seem to find a voltage comparator like this.

I have never seen one. But why look for a chip when it is so easy to connect a voltage reference to one input of a standard comparator?

Voltage reference

and the zener diode voltage may not be accurate.

The zener diode voltage will not be accurate.

3

Googling "brownout detector chip" and "voltage supervisor chip" got me to the MCP100.
Current draw is ~45uA.
You could tell us why, and what the rest of your circuit looks like.
There might be other ways.
Leo..

4

Yea I figured it doesn't exist. Too much work for the manufacturer to custom-build the IC's with different Vref values per chip. I know it's not hard to connect a voltage reference, but I was just having some wishful thinking of a chip that has everything built in. Thanks!

5

All I'm doing is comparing the battery voltage of a Lipo to 3.3V to see if the battery is low or not. Was wondering what the most compact way of doing it is (least number of components). All I need to read is logic high/low, or open drain if I use an internal pullup resistor on the MCU.

6

An Arduino can measure it's own VCC internally (code only).
https://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/
Leo..

7

androidfanboy:
All I'm doing is comparing the battery voltage of a Lipo to 3.3V to see if the battery is low or not. Was wondering what the most compact way of doing it is (least number of components). All I need to read is logic high/low, or open drain if I use an internal pullup resistor on the MCU.

Why don't you do the comparison in software?
Use an potential divider to an analog input, if you are using a UNO or such, use the 1.1V internal reference.
Very little extra hardware.
Tom... :slight_smile:

8

Yea, but the ADC doesn't seem to be very accurate (on my ESP8266) and each one requires calibration, and I want the threshold fixed at 3.3V anyway.

9

androidfanboy:
So basically the chip would have a total of four pins: VCC, GND, V+, and OUT.

I can't seem to find a voltage comparator like this.

Not seen one with 4 pins, most of the voltage supervisors are 3 pins as thats all they need.

There are plenty of them, range of voltages (3.3V certainly) current consumption as low as 1uA, open drain etc.

10

Wait, so you're saying that there's a chip that does exactly what I want (low voltage detection with open drain output) that only requires 3 pins? That would be perfect! I'm assuming there's only VCC, GND, and OUT. Would you mind giving me an example?

Thanks!

11

androidfanboy:
Wait, so you're saying that there's a chip that does exactly what I want (low voltage detection with open drain output) that only requires 3 pins? That would be perfect! I'm assuming there's only VCC, GND, and OUT. Would you mind giving me an example?

Thanks!

Look at answer #2.

12

How about this? but is 6 pins

TPS3808 Low-Quiescent-Current, Programmable-Delay Supervisory Circuit

13

I want to attach the battery supervisor IC directly to the LiPo voltage. Also, I have solidified that I need an open-drain output (not push-pull like I mentioned before).

Would this work? Can I attach the supervisor directly to the LiPo voltage? It says VCC can go up to 6V. All the spec sheets for these supervisor chips seem to indicate that the supervisor is connected to the same VCC as the MCU logic.

14

Better yet, a 3-pin one like this one? I just need to make sure that if I tie VDD directly to the LiPo, and if I select a chip with 3.3V threshold, then I will get the output I want (active low, open drain, with pullup resistor on an input pin).

Sounds like I need a "voltage detector" rather than a "supervisor".

15

androidfanboy:
Wait, so you're saying that there's a chip that does exactly what I want (low voltage detection with open drain output) that only requires 3 pins? That would be perfect! I'm assuming there's only VCC, GND, and OUT. Would you mind giving me an example?

TC54 for instance, not sure if thats available in a 3.3V version but ther are others that are. I used a 2.9V TC54 to force a circuit into reset when a 3V regulator had failed. Available in open drain and push pull.

16

Thanks! Yes, something like the TC54 is what I need (voltage detector). Can this be tied directly to the LiPo battery? I'm just trying to read HIGH/LOW whether the battery is below 3.3V or not.

17

androidfanboy:
Better yet, a 3-pin one like this one? ...

I think you can use this one. You can use any supervisor circuit, it should be OK connect it to other voltage than the MCU (and pull-up to MCU power).
There are circuits dedicated to protect Li-xxx batteries (both overcharge and overdischarge), maybe you may want to look at those. For example I got CS213 from an ancient device powered by (long dead) Li-ion battery.

18

Awesome, thanks! So just to confirm, when the LiPo battery voltage falls below 3.3V, it will pull the VOUT pin to GND, but normally it's open-drain and I can use a pullup resistor on my input pin?

Also, can I use a 1M pullup resistor to decrease the parasitic current drain through the pullup when the battery goes low? I'm just not sure how high of a resistance I can use.