CPC5712

R02

www.ixysic.com

9

3.3.2 Verify Resistor Selection

Once the resistor values are chosen it is necessary to

back calculate the nominal detector thresholds.

To do this the following equations are provided for two

variables:

the reference voltage output.

The following values are also needed to perform the

threshold calculations. They are:

which gives:

and

The threshold equations are:

1.

2.

3.

4.

Using the selected standard 1% resistor values, and

back calculating to the threshold voltages produces

these results:

As can be seen, the error from using standard value

3.4 High Voltage Detection Designs

Designs that require higher detection levels greater

than approximately 17V will necessitate a different

voltage divider ratio to accommodate the operational

range of the CPC5712’s internal circuitry. Changes to

the input resistor divider network are restricted to the

high impedance resistors from the tip and ring leads to

the IN+ and IN- inputs. Changing the differential input

resistor value from 806k

 is not recommended as this

will introduce offset errors. The degree of offset error

caused by changing this component’s value is not

measured and therefore not calculable.

The design procedure for higher voltage detect levels

is the same as presented above. Remember to begin

with the equations shown in Section 2.5 “Detector

Threshold Operation” on page 6 and use the

updated value for the “A” term based on the new input

resistor values.

++

=

R1 R2 R3 R4 R5

++++

=





----------------------------------------

=

+







-----------------------------------------------------

=

++







------------------------------------------------------------------

=

+++







--------------------------------------------------------------------------------

=