MC33121
MOTOROLA
1
Thin Film Silicon Monolithic Integrated Circuit
The MC33121 is designed to provide the interface between the 4–wire side of
a central office, or PBX, and the 2–wire subscriber line. Interface functions
include battery feed, proper loop termination AC impedance, hookswitch
detection, adjustable transmit, receive, and transhybrid gains, and single/
double fault indication. Additionally, the MC33121 provides a minimum of 58 dB
of longitudinal balance (4–wire and 2–wire).
The transmit and receive signals are referenced to analog ground, while
digital signals are referenced to digital ground, easing the interface to codecs,
filters, etc. The 2 status outputs (hookswitch and faults) and the Power Down
Input are TTL/CMOS compatible. The Power Down Input permits local
shutdown of the circuit.
Internal drivers allow the external loop current pass transistors to be standard
bipolar transistors (non–Darlington).
The MC33121 is available in a 20 pin DIP and a 28 pin PLCC surface mount
package.
58 dB Longitudinal Balance Guaranteed; 4–wire and 2–wire
Transmit, Receive, and Transhybrid Gains Externally Adjustable
Return Loss Externally Adjustable
Proper Hookswitch Detection With 30 k
Leakage
Single/Double Fault Indication With Shutdown for Thermal Protection
Critical Sense Resistors Included Internally
Standard Power Supplies: – 21.6 V to – 42 V, and + 5.0 V,
±
10%
On–Hook Transmission
Power Down Input (TTL and CMOS Compatible)
Operating Ambient Temperature: – 40
°
C to + 85
°
C
Available in a 20 Pin DIP and 28 Pin PLCC Package
SIMPLIFIED BLOCK DIAGRAM
–
+
+
–
+
–
–
+
VCC
EP
BP
CP
TSI
RSI
CN
BN
EN
VEE
(BATTERY)
TIP
RING
VEE
VCC
*
*
*
*
CURRENT
MIRROR
HOOK STATUS AND
FAULT DETECTION
AND BIAS CONTROL
BIAS
MC33121
VDD (+5.0 V)
VDG
(DIG. GND)
PDI/ST2
ST1
VAG
(ANA. GND)
RXI
TXO
RFO
CF
VQB
* Indicates trimmed resistor
CURRENT
MIRROR
CURRENT
MIRROR
CURRENT
MIRROR
CURRENT
MIRROR
CURRENT
MIRROR
Order this document
by MC33121/D
SEMICONDUCTOR TECHNICAL DATA
ORDERING INFORMATION
P SUFFIX
PLASTIC PACKAGE
CASE 738
FN SUFFIX
PLCC
CASE 776
MC33121P
MC33121FN
Plastic DIP
PLCC
– 40
°
to + 85
°
C
Device
Temperature
Range
Package
20
1
28
1
REV 1.0
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