MH88437-P
+5V
C2
+
9 25 24
VLOOP1
VLOOP2
VCC
R2
21
22 13 11
LOOP
RS
R7
C8
28
L2
R1
R4
5
4
3
16
15
6
1
2
CL
ZB
R3
R5
R6
C4
C5
C6
Analog
Output
Analog
Input
Analog
Input
Ringing Voltage Detect Output
Loop Current Detect Output
Loop Control Input
TIP
TIP
VX
VR-
MH88437
VR+
RV
D1
D2
C1
L1
RING
23
RING
AGND VBIAS
10
26 8
C9
C3 +
ZA
7
LCD
LC
NB1
NB2
C7
Zext
Notes:
1) R1 & C1: Dummy Ringer, country specific
typically 0.39µF, 250V & 3kΩ
2) R2: DC Mask Resistor 82kΩ typical
3) R3 & R4: Transmit Gain Resistors
≥
2k2
4) R5 = R6: Receive Gain Resistors typically 100k
5) ZB: Network Balance Impedance
6) C2 & C3 = 10µF 6V
7) C7 & C8 = 39nF for 12kHz filter and 22nF for
16KHz filter. These can be left off if meter pulse
filtering not required.
8) Zext: External Impedance
9) D1 Zener Diode 9V1 (x2)
10) L1, L2 = 4.7mH RDC<10Ω. These can be left
off if meter pulse filtering not required.
11) C4, C5 & C6 = 1µF coupling capacitors
12) R7 = 620kΩ (30V RMS ringing sensitivity)
13) D2 = Teccor P2703 Protection
14) C9 = 22nF
=
Ground (Earth)
Figure 5 - Typical Application Circuit
7
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