Max8211 Voltage Detector Circuit ??

[rainyday101]

Hi, I have a diagram attached of a simple circuit I am trying to implement. This is the link for the spec. sheet: https://pdfserv.maxim-ic.com/en/ds/MAX8211-MAX8212.pdf On page 5 of the datasheet I am setup for the low voltage detector shown in figure 5. I calculated a value of 6.8k for R3 to get a hysteresis of 75mV. I am looking for a Vlow/trip voltage of 2.3V. By coincedence this makes the calculation of R2 simple, it will always equal R1. I am using 100K for both R1 and R2.

My problem is the output! I hook a LED to the output pin (pin 4) and it lights when the battery voltage is say 3Vdc. When the threshold voltage gets below the specified 1.15 reference voltage I don't see a switch in the output state. This may be as simple as me not understanding the output, which is a N-channel MOSFET. Also I would like the LED to remain off at high battery voltage and come on when the battery level gets below 2.3V. Here is the quote from the datasheet detailed description: " The MAX8211 output N-channel turns on when the voltage applied to the THRESH pin is less than the internal reference (1.15V). The sink current is limited to 7mA, allowing direct drive of an LED without a series resistor.

Any ideas what I am doing wrong?

 

[KMoffett]

Since the output is a "current sink", you need to connect the anode of the LED to V+ and the cathode to pin 4.

Ken

 

[rainyday101]

Okay, I made that correction and attached is my circuit with revisions. I know this circuit is simple, but I can't get it to work. With the batteries at 2.7v, I get the following readings:

• pin 2 - .96v
• pin 3 - .5v
• pin 4 - .95v
• LED on

Also if I remove the IC from the proto board I get 2.7v at the intersection of R1 and R2. It seems as if the IC is pulling the voltages down. I do not see a change in the output on pin 4 with the supply voltage lower than 1.15v IC reference. I have tried another chip and get the same results.

Any Ideas?

 

[KMoffett]

If I have time today I'll duplicate your circuit and see what I get.

Ken

 

[rainyday101]

Thanks, I know I have been out of the circuit end of the bussiness for some time now, but I also know that this circuit should be a simple no-brainer. Unfortunately it seems to be getting the best of me! Thanks for the help!

 

[KMoffett]

OK, I'm using an ICL8212, an earlier version of the MAX8212, a 5.6KΩ instead of the 6.8KΩ(insignificant change), and the LED from V+ to pin4. The LED switched on and off at ~2.3V at V+.

Recheck your wiring...better, start from scratch and verify each connection.

Ken