CPC5712 Ver la hoja de datos (PDF) - IXYS CORPORATION
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CPC5712 Datasheet PDF : 11 Pages
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INTEGRATED CIRCUITS DIVISION
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:
R = RIN1 + RIN2 + RDIFF
RREF = R1 + R2 + R3 + R4 + R5
where R is the sum of the resistive interface network
and RREF is the sum of the resistor divider network on
the reference voltage output.
The following values are also needed to perform the
threshold calculations. They are:
• VREF = 1.5V
• RIN1 = RIN2 = 2 x 10M = 20M
• RDIFF = 806k
• G=2.5 (Single ended gain of input amplifier)
which gives:
• R = 40.806M and
• RREF = 270.1k
The threshold equations are:
1.
VL1 = -G--V----R--R-E---DF----I--F--R-F-------R---R-R---1E---F-
2.
VH1 = V----R---GE---F------R--R--D---I--F---F---R----R1----R-+--E---RF----2---
3.
VL2 = V----R---E---F----G----R----R----D----I-R-F---F1-----+--R---R-R---2E---F-+-----R----3----
4.
VH2 = V----R---E---F--------R--G---------R--R--D--1-I--F--+-F----R---R-2---R-+--E---RF----3-----+----R----4----
CPC5712
Using the selected standard 1% resistor values, and
back calculating to the threshold voltages produces
these results:
• VL1 = 3.00280V
• VH1 = 5.00467V
• VL2 = 11.9662V
• VH2 = 14.9690V
As can be seen, the error from using standard value
resistors is less than 0.1% for VL1 and VH1 and is less
than 0.3% for VL2 and VH2.
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.
R02
www.ixysic.com
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