am79r251 Advanced Micro Devices, am79r251 Datasheet - Page 23

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

Table 3.
Thermal-Management Equations (All Modes except Standby)
Driver Descriptions
Control bits RD1, RD2, and RD3 do not affect the operating mode of the Am79R251. These signals
usually perform the following functions.
I
P
P
I
P
P
L
L
SLIC
TMG
SLIC
TMG
< 5 mA
> 5 mA
Driver
R1
R2
R3
= (S
= 0
= (S
= (I
L
BAT
BAT
– 5 mA)^2 • (R
– I
– I
LRL
L
(R
A logic 1 on RD1 turns the R1 driver on and operates a relay connected between the R1
pin and VCCD. R1 drives the ring relay when external ringing is selected.
A logic 1 on the RD2 signal turns the R2 driver on and routes current from the R2 pin to
the RYE pin. In the option where the RYE pin is connected to ground, the R2 pin can sink
current from a relay connected to VCCD.
Another option is to connect the RYE pin to the BD (Ring) lead and connect a test load
between R2 and the AD(Tip) lead. This technique avoids the use of a relay to connect a
test load. However, it does not isolate the subscriber line from the linecard. The test load
must be connected to the Am79R251 side of the protection resistor to avoid damage to
the R2 driver.
A logic 1 on the RD3 signal turns the R3 driver on and routes current from the R3 pin to
the RYE pin. In the option where the RYE pin is connected to ground, the R3 pin can sink
current from a relay connected to VCCD.
Another option is to connect the RYE pin to the B (Ring) lead and connect a test load
between R3 and the A(Tip) lead. This technique avoids the use of a relay to connect a
test load. However, it does not isolate the subscriber line from the linecard. The test load
must be connected to the Am79R251 side of the protection resistor to avoid damage to
the R3 driver.
) • I
L
+ 2 • R
L
+ 0.3 W
TMG1
FUSE
+ R
))*I
TMG2
L
Am79R251
+ 0.3 W – P
)
TMG
Description
TMG resistor-current is limited to be 5 mA < I
If I
and it all flows in the Am79R251.
These equations are valid when
R
because the longitudinal voltage is one-half the
battery voltage and the TMG switches require
approximately 2 V.
TMGX
L
< 5 mA, no current flows in the TMG resistor
• (I
L
– 5 mA) < (S
BAT
– R
L
I
L
)/2 – 2
L
23
.