rs08 internal voltage regulator ... what does it do?

[PeterK]

Hi,
  I am using the KA2 and KA8 parts ..    they are great little parts!!

 For a cost sensitive project I am considering the need for
an external voltage regulator. Vcc will initially be 4.5v and
over the life of the supply battery drop to around 3v.
Core activity is to measure temperature using a thermistor and
a reference resistor and then to manipulate a relay as determined by the code.

The KA2 datasheet mentions that the parts have an internal
voltage regulator that will drop the supplied voltage to a lower level
and I am wondering what this level is and if it is fixed .. and really
if this internal voltage regulation will be sufficient for my project and
that external regulation is not really needed for such a simple task.

Will somebody in the know provide a little more detail about the
internal voltage regulator?

Thanks a lot.

Peter K

[bigmac]

Hello Peter,

For this application, I assume you would be using the KA8 device, with the availability of an ADC module.  It would appear that the voltage regulator that you refer to is used internally, but does not affect the operation of this module.  The reference voltage for the ADC would use internal connections to Vdd and Vss.

However, if the thermistor and resistor were to be series connected between Vdd and Vss, with the junction applied to an ADC input, the measurement would be ratiometric, and independent of actual Vdd level.  With the thermistor in the upper leg, the ADC output value would be represented by the formula -

N = Nmax / (1 + Rth / R)

This would give an increasing value for increase of temperature (assuming NTC thermistor), but would be quite non-linear.

Regards,

Mac