CPC5712
In the case of the detector 2 switching points, DET2
will be low after the |TIP/RING| voltage has decreased
below a threshold set at VL2. DET2 will not transition
high until after the |TIP/RING| voltage has increased
above a threshold set at VH2. This |TIP/RING| voltage
will be larger than the threshold set at VL2. As an
example, the voltage at VL2 represents a |TIP/RING|
threshold of 20V and VH2 represents a TIP/RING
threshold of 22V. DET2 will be low if the |TIP/RING|
voltage decreases below 20V, and it will remain low
until the |TIP/RING| voltage increases above 22V.
DET2 will change states for both positive and negative
values of TIP/RING voltage as represented by
|TIP/RING|. This means that DET2 will also be low if
the TIP/RING voltage decreases below -20V and will
remain low until the TIP/RING voltage increases
beyond -22V. The user must rely on POLARITY to
determine whether the TIP/RING threshold changed
due to a positive or negative differential signal since
DET2 does not contain any polarity information.
V
: An analog output that is similar to the DC bias
REF
level that is applied to OUT+ and OUT-. This voltage is
brought off chip so that it can be used to define
threshold detection levels. Load capacitance on this
pin must be kept less than the value recommended in
the table Recommended Operating Conditions.
The total load resistance on this pin must be within the
range specified in the table Recommended
Operating Conditions.
Resistors R1, R2, R3, R4 and R5 are external
resistors, which must be provided by the user. The
selection of the resistors determines the voltages at
VL2, VH2, VL1 and VH1 and therefore the threshold and
hysteresis values for the 2 detectors.
The values for R1, R2, R3, R4, and R5 are easily
st
nd
determined. Select voltage levels for the 1 and 2
threshold and hysteresis settings such that:
VH2 > VL2 > VH1 > VL1
DET1 behaves similarly to DET2, except that it is
triggered based on the voltage set at VL1 and VH1.
This means that DET1 will be low after the |TIP/RING|
voltage has decreased below the value set by the
voltage at VL1 and will not change high until after the
|TIP/RING| voltage has increased above the value set
by the voltage at VH1. DET1 does not give any polarity
information for the same reasons as defined for DET2.
In the application circuit provided, the TIP/RING
threshold levels of DET2 will always be higher than the
threshold levels of DET1.
Then use the following algorithm to find the values of
R2, R3, R4 and R5.
1. Select a value for R1.
2. R2 = (R1(VH1-VL1)) / VL1
3. R3 = (R1(VL2-VH1))/ VL1
4. R4 = (R1(VH2-VL2)) / VL1
5. R5 = (R1(VREF/A-VH2)) / VL1
• VREF = 1.5V
• A = (2.5 (RDIFF)) / (RIN1 + RIN2 + RDIFF), which
typically calculates to 0.05; in this case: 0.04938.
See Figure 2.
Also, as shown in the table of Recommended
Operating Conditions, the resistive load on the VREF
pin must fall within the range:
2.5 Detector Threshold Operation
VL1, VH1, VL2, and VH2: Inputs used to set the
|TIP/RING| threshold levels that are to be detected.
V
H1 and VL1 are used to set the high and low threshold
20kΩ < (R1 + R2 + R3 + R4 + R5) < 1MΩ
levels. The difference between VH1 and VL1 sets the
st
hysteresis for the 1 threshold level. VH2 and VL2 are
nd
used to set the threshold and hysteresis for the 2
2.6 Power Connections
VCC, Ground: Power supply pins. These are used to
supply voltage and ground to the chip.
st
threshold level. There is a digital output for both the 1
nd
and 2 threshold levels that shows when the
|TIP/RING| voltage has crossed a threshold level and
when it has exceeded the configured hysteresis level.
This was explained in the DET1 and DET2 definitions.
In general, the digital output will be low when the
|TIP/RING| voltage has fallen below the VL# level and
will change high again once the |TIP/RING| voltage
has risen above the VH# level.
6
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