LTC2846 datasheet(18/24 Pages) LINER

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LTC2846

sn2846 2846fs

+ (VEE • IEE) – ND • PRT

(3)

Since power is drawn from the supplies of the LTC2846

(VCC, VDD and VEE) at less than 100% efficiency, the

LTC2846 dissipates extra power to source PDISS(2845) and

PRT :

PDISS1(2846) = 125% • (VCC • ICC) + 125% • 125%

•(VDD • IDD) + 125% • 143% • (VEE • IEE)

– PDISS(2845) – ND • PRT

= 25% • (VCC • ICC) + 56% • (VDD • IDD)

+ 79% • (VEE • IEE)

(4)

From the LTC2845 Electrical Characteristics Table, for

VCC = 5V, VDD = 8V and VEE = – 5.5V:

ICC at no load

2.7mA

ICC at full load with all drivers high

110mA

IEE at no load

2mA

IEE at full load with both V.10 drivers low

23mA

IDD at no load

0.3mA

IDD at full load

0.3mA

The V.11 drivers are driven between VCC and GND while

the V.10 drivers are driven between VCC and VEE. Assume

that the V.11 driver outputs are high and V.10 driver

outputs low. Current going into each 100

Ω V.11 receiver

termination = (110mA – 2.7mA) – 23mA/3 = 28.1mA.

Current going into each 450

Ω V.10 receiver termination =

23mA – 2mA/2 = 10.5mA. From Equation (2), V.11 PRT =

79mW and V.10 PRT = 49.6mW.

From Equation (3), PDISS(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), PDISS1(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. (651) 639-0775

Fax (651) 639-0873

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