MH88400
Preliminary Information
14
13
TIP
R1
11
MH88400
TIP
RLS
6
VX
7
Audio Output
VR
TF
Audio Input
D1
R2
C2
10
TXIN
RVLC
4
Ring Voltage & Loop
Current Detect Output
RING
Line
Relay
Input
9
3
RING
VDD
1
AGND
2
+
C1
+5V
1) R1: 39Ω,1/2W,5%,current
limiting resistor for use in
Germany.
2) R2: 18kΩ
3) C1: 10µF, 6V Tantalum
4) C2: 0.47µF, 100V
LC
Loop Control Input
K1
5) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180
6) VX and VR are biased at 2.5V, therefore, coupling capacitors
may be required depending on application.
NOTES:
C2 must be 0.1µF for correct operation. R2 & C2 form a dummy ringer, where R2 is on the hybrid and C2 must be fitted by
the customer. To initate a manual call, lift the handset. The RVLC pin will indicate that the line as been seized by the
monitor phone. The required number is then dialled and the connections established. During this phase the Loop Control
input should be turned ON to ensure that when the relay K1 is operated and the monitor phone removed from the line loop
current is still maintained. On receipt of the correct progress tones the external controller should control the data transmission
and clear down the call when it is completed by turning the Loop Control OFF. For applications in some countries such as
Germany the MH88422 can not be used with an optional telephone but may still be used in a combined telephone/fax machine.
Figure 4 - Typical Application Circuit with Dummy Ringer and Monitor Phone
R4
1K
Audio Output
14
13
TIP
R1
11
C2
D1
10
9
TIP
RLS
MH88400
6
VX
R3
1K
7
VR
R2
100K
4
RVLC
Ring Voltage & Loop
Current Detect Output
3
Audio Input
TF
TXIN
RING
RECEIVE GAIN:
Audio input to Tip-Ring
=20log(R2/(R2+47K))+3.5dB
=6.5dB
TRANSMIT GAIN:
Tip-Ring to Audio Output
=20log(R4(R3+R4))-0.4dB
=-6.4dB
Note:
The VX output gain has been reduced by 6dB
(to -6.4dB) and the VR input gain has been
reduced by 10dB (to -6.5dB) in this example.
RING
VDD
AGND
2
+
C1
+5V
LC
Loop Control Input
1
1) R1: 39Ω,1/2W,5%,current limiting resistor for use in Germany
2) C1: 10µF, 6V Tantalum
3) C2: 0.1µF, 250V (Typical Value)
4) D1: 180VDC Foldback Diode, e.g. TISP4180, TISP5180
5) VX and VR are biased at 2.5V, therefore, coupling capacitors
may be required depending on application.
6) (R3+R4) should be > 2kΩ to prevent overload.
Figure 5 - Typical Application Circuit for Gain Adjustment
2-18
MITEL [ MITEL NETWORKS CORPORATION ]
