Datasheet

18
LTC2846
sn2846 2846fs
+ (V
EE
• I
EE
) – N
D
• P
RT
(3)
Since power is drawn from the supplies of the LTC2846
(V
CC
, V
DD
and V
EE
) at less than 100% efficiency, the
LTC2846 dissipates extra power to source P
DISS(2845)
and
P
RT
:
P
DISS1(2846)
= 125% • (V
CC
• I
CC
) + 125% • 125%
•(V
DD
• I
DD
) + 125% • 143% • (V
EE
• I
EE
)
– P
DISS(2845)
– N
D
• P
RT
= 25% • (V
CC
• I
CC
) + 56% • (V
DD
• I
DD
)
+ 79% • (V
EE
• I
EE
) (4)
From the LTC2845 Electrical Characteristics Table, for
V
CC
= 5V, V
DD
= 8V and V
EE
= –5.5V:
I
CC
at no load 2.7mA
I
CC
at full load with all drivers high 110mA
I
EE
at no load 2mA
I
EE
at full load with both V.10 drivers low 23mA
I
DD
at no load 0.3mA
I
DD
at full load 0.3mA
The V.11 drivers are driven between V
CC
and GND while
the V.10 drivers are driven between V
CC
and V
EE
. Assume
that the V.11 driver outputs are high and V.10 driver
outputs low. Current going into each 100Ω V.11 receiver
termination = (110mA – 2.7mA) – 23mA/3 = 28.1mA.
Current going into each 450Ω V.10 receiver termination =
23mA – 2mA/2 = 10.5mA. From Equation (2), V.11 P
RT
=
79mW and V.10 P
RT
= 49.6mW.
From Equation (3), P
DISS(2845)
= 5V • (110mA – 23mA) +
(8V • 0.3mA) + 5.5V • 23mA – 3 • 79mW – 2 • 49.6mW =
228mW. Since the LTC2845 runs slow control signals, the
AC power dissipation can be assumed to be equal to the DC
power dissipation.
The extra power dissipated in the LTC2846 due to LTC2845
is given by Equation(4), P
DISS1(2846)
= 25% • (5V • 87mA)
+ 56% • (8V • 0.3mA) + 79% • (5.5V • 23mA) = 210mW.
So for an X.21 DCE port running at 10MBd, the LTC2846
dissipates approximately 918mW + 210mW = 1128mW
while the LTC2845 dissipates 228mW.
Compliance Testing
The LTC2846/LTC2844 and LTC2846/LTC2845 chipsets
have been tested by TUV Rheinland of North America Inc.
and passed the NET1, NET2 and TBR2 requirements.
Copies of the test reports are available from LTC or TUV
Rheinland of North America Inc.
The title of the reports are Test Report No.:
TBR2/051501/02 and TBR2/050101/02
The address of TUV Rheinland of North America Inc. is:
TUV Rheinland of North America Inc.
1775, Old Highway 8 NW, Suite 107
St. Paul, MN 55112
Tel. [phone]
Fax [phone]
TYPICAL APPLICATIO S
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