am79r251 Advanced Micro Devices, am79r251 Datasheet - Page 8

• Manufacturer Part Number: am79r251
• Description: Intelligent Subscriber Line Interface Circuit Islic
• Manufacturer: Advanced Micro Devices

PIN DESCRIPTIONS
8
AD, BD
BGND
CREF
GND
HPA, HPB
ILG
IMT
LD
P1–P3
R1
R2
R3
RSN
RSVD
RYE
SA, SB
TMP,
TMN, TMS
VBH
VBL
VBP
VCC
VLB
VREF
VSAB
VTX
Pin
A, B Line Drivers
Ground
+3.3 VDC
Ground
High-Pass Filter
Capacitor
Longitudinal Current
Sense
Metallic Current Sense
Register Load
Control Bus
Relay 1 Driver
Relay 2 Driver
Relay 3 Driver
Receive Summing
Node
Reserved
Relay 2, 3 Common
Emitter
A, B Lead Voltage
Sense
Thermal Management
Battery (Power)
Battery (Power)
Positive Battery
(Power)
+5 V Power Supply
Longitudinal Voltage
1.4 V Analog
Reference
4-Wire Transmit Signal
Loop Voltage
Pin Name
I/O
O
O
O
O
O
O
O
O
O
O
I
I
I
I
I
I
IMT is proportional to the differential line current (IAD + IBD), except in disconnect mode,
Collector connection for relay 1 driver. Emitter internally connected to BGND.
Collector connection for relay 2 driver. Emitter internally connected to RYE
Collector connection for relay 3 driver. Emitter internally connected to RYE.
External resistors connected from TMP to TMS and TMN to VBL to offload excess power
Provide the currents to the A and B leads of the subscriber loop.
Ground return for high and low battery supplies.
VCCD reference. It is the digital high logic supply rail, used by the ISLIC to ISLAC interface.
Analog and digital ground return for VCC.
These pins connect to CHP, the external high-pass filter capacitor that separates the DC
loop-voltage from the voice transmission path.
ILG is proportional to the common-mode line current (IAD – IBD), except in disconnect mode,
where ILG is proportional to the current into grounded SB.
where IMT is proportional to the current into grounded SA.The Am79R251 indicates thermal
overload by pulling IMT to CREF.
The LD pin controls the input latch and responds to a 3-level input. When the LD pin is a
logic 1 ( >(Vref + 0.3V) ), the logic levels on P1–P3 latch into the Am79R251 control register
bits that operate the mode-decoder. When the LD pin is a logic 0 ( <(Vref – 0.3V) ), the logic
levels on P1–P3 latch into the Am79R251 control register bits that control the relay drivers
(RD1–RD3). When the LD pin level is at ~VREF, the control register contents are locked.
Inputs to the latch for the operating-mode decoder and the relay-drivers.
The metallic current between AD and BD is equal to 500 times the current into this pin.
Networks that program receive gain and two-wire impedance connect to this node. This input
is at a virtual potential of VREF.
This is used during AMD testing. In the application, this pin must be left floating.
Emitter connection for R2 and R3. Normally connected to relay ground.
Sense the voltages on the line side of the fuse resistors at the A and B leads. External sense
resistors, RSA and RSB, protect these pins from lightning or power-cross.
from the Am79R251.
Connection to high-battery supply used for ringing and long loops. Connects to the substrate.
When only a single battery is available, it connects to both VBH and VBL.
Connection to low-battery supply used for short loops. When only a single battery is available,
this pin can be connected to VBH.
Used in Ringing State and for Extended Loop operation.
Positive supply for low voltage analog and digital circuits in the Am79R251.
Sets the DC longitudinal voltage of the Am79R251. It is the reference for the longitudinal
control loop. When the VLB pin is greater than VREF, the Am79R251 sets the longitudinal
voltage to a voltage approximately half-way between the positive and negative power supply
battery rails. When the VLB pin is driven to levels between 0V and VREF, the longitudinal
voltage decreases linearly with the voltage on the VLB pin.
The ISLAC chip provides this voltage which is used by the Am79R251 for internal reference
purposes. All analog input and output signals interfacing to the ISLAC chip are referenced
to this pin.
Scaled-down version of the voltage between the sense points SA and SB on this pin.
The voltage between this pin and VREF is a scaled down version of the AC component of
the voltage sensed between the SA and SB pins. One end of the two-wire input impedance
programming network connects to VTX. The voltage at VTX swings positive and negative
with respect to VREF.
Am79R251
Description