Voltage divider for reference

[thirsty]

Hi All,

I have a sensor that outputs (using a 5V supply) a voltage between about .5V to 4.5V representing the lower limit to the upper limit of it's measurement.

I'm using the onboard ADC on a pic 16f913 and I want to set the Vref- and Vref+ inputs on the ADC to match the sensor so I can utilise all of the ADC's resolution.

Is a simple voltage divider with resistors between GND and VCC sufficient? I would dearly love not to use any more IC's to keep the cost down and also keep the device as small as possible.

Thanks in advance for any help/suggestions,

Thirsty

[Acetronics]

TL 431 ???? TO 92 case ... and adjustable.

Pressure, altitude and speed insensitive too ... :D :D :D

Alain

[Dan Baldwin]

Yes, if you are confident that your 5 volt supply is accurate enough for the precision you are looking for, you can use a voltage divider for VREF+ and VREF-. The maximum suggested source impedance is 10K, so you should keep the resistances fairly small. A 3 resistor ladder using a 1K, 8K, and another 1K resistor should work fine.

As Alain says, you can also use a voltage reference (like the TL431) for the VREF+, and a 2 resistor ladder for the VREF-.

Dan

[jeffs555]

Most 5 volt regulators have only 2% to 5% tolerance. The TL431 is available to 0.5% or better. However, if the output of your sensor is referenced to the 5 volt supply, you could get better accuracy by using a voltage divider off the 5 volts.

[thirsty]

Thanks guys. The sensor is referenced off the 5V supply so I figured any fluctuations would appear at the ADC as well cancelling each other out.

I'm using a Microchip MCP1252 for power due to the possibility of the input being anywhere from less than 5 volts to over 6 volts. I guess I'll have to decouple this pretty well so no ripple appears on the power lines.

I'll try the voltage divider first and see how that goes then,

Thirsty