參數(shù)資料
型號： MC33121
廠商： Motorola, Inc.
英文描述： LOW VOLTAGE SUBSCRIBER LOOP INTERFACE CIRCUIT
中文描述： 低電壓用戶環(huán)路接口電路
文件頁數(shù)： 14/32頁
文件大小： 570K
代理商： MC33121
MC33121
14
MOTOROLA
Logic Interface (Hook status, pulse dialing, faults)
The logic interface section provides hookswitch status,
fault information, and pulse dialing information to the 4–wire
side of the system at the ST1 and ST2 outputs. Figure 30 is
a representative diagram.
The logic outputs operate according to the truth table in
Table 1:
Table 1. Status Output Truth Table
Hook
Status
Fault
Detection
Outputs
Circuit Condition
i C
di i
ST1
ST2
On–Hook
Off–Hook
On–Hook
Off–Hook
No Fault
No Fault
Fault
Fault
Hi
Lo
Lo
Lo
Lo
Hi
Lo
Lo
Internally powered down
Powered up
Internally powered down
Internally powered down
Referring to Figure 30, ST1 is configured as an active NPN
pulldown with a 15 k
pullup resistor. ST2 has a 800
μ
A
current source pullup, and a 1.0 mA current source for a pull-
down. Current limiting this output controls the discharge from
the external capacitor when ST2 switches low.
The condition where both ST1 and ST2 are high is not
valid, but may occur momentarily during an off–hook to on–
hook transition. The condition where both ST1 and ST2 are
low may occur momentarily during an on–hook to off–hook
transition — this should not be interpreted as a fault con-
dition. ST1 and ST2 are TTL/CMOS compatible and are
powered by the + 5.0 V supply (VDD). Refer to the Applica-
tions Section for more details.
Power Supplies, Grounds
The MC33121 requires 2 power supplies: battery voltage
between – 21.6 V and – 42 V (VEE), and an auxiliary voltage
between + 4.5 V and + 5.5 V (VDD).
VEE is nominally – 24 V, with a typical range of – 21.6 V to
– 42 V, and must be referenced to VCC (battery ground). A
0.1
μ
F bypass capacitor should be provided between VCC
Figure 29. Receive Path
–
+
–
+
–
+
VCC
EP
BP
BN
EN
VQB
IT
RING
TIP
RL
IA = IRXI
30
3060
IA
30
3060
IA
VDD
VQB
VAG
IRXI
RXI
RRX
VRX
RP
TO VEE
IT
20
19
18
3
2
6
9
10
MIRROR
VL
RP
MC33121
Figure 30. Logic Interface
HOOK
SWITCH
RL
TIP
RING
RC
RSI
TO LOOP
CURRENT
DRIVERS
BIAS
CIRCUIT
HOOK STATUS
DETECTION
FAULT
DETECTION
OFF–HOOK
ON–HOOK
FAULT
50 k
800
μ
A
15 k
VDD
VDD
15
1.0 mA CT
5.0
μ
F
STATUS 1
STATUS 2
EXTERNAL
POWER DOWN
CONTROL INPUT
RC
RS
RS
TSI
CN
CP
50 k
ST2/PDI
ST1
VDG
12
13
14
MC33121
+5.0 V
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