OPA2674_17 Datasheet, PDF(19/36 Page) Texas Instruments – Dual Wideband, High Output Current Operational Amplifier with Current Limit

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OPA2674_17 Datasheet, PDF (19/36 Pages) Texas Instruments – Dual Wideband, High Output Current Operational Amplifier with Current Limit

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+VCC

Figure 8. Line Driver Headroom Model

Table 1 gives V1, V2, R1, and R2 for both +12V and +5V op-

eration of the OPA2674.

Table 1. Line Driver Headroom Model Values

+5V

0.9V

5â¦

0.8V

5â¦

+12V

0.9V

2â¦

0.9V

2â¦

TOTAL DRIVER POWER FOR xDSL

APPLICATIONS

The total internal power dissipation for the OPA2674 in an

xDSL line driver application will be the sum of the quies-

cent power and the output stage power. The OPA2674

holds a relatively constant quiescent current versus supply

voltageâgiving a power contribution that is simply the

quiescent current times the supply voltage used (the sup-

ply voltage will be greater than the solution given in Equa-

tion 10). The total output stage power may be computed

with reference to Figure 9.

+VCC

IAVG

Figure 9. Output Stage Power Model

The two output stages used to drive the load of Figure 7

can be seen as an H-Bridge in Figure 9. The average cur-

rent drawn from the supply into this H-Bridge and load will

OPA2674

SBOS270C â AUGUST 2003 â REVISED AUGUST 2008

be the peak current in the load given by Equation 8 divided

by the crest factor (CF) for the xDSL modulation. This total

power from the supply is then reduced by the power in RT

to leave the power dissipated internal to the drivers in the

four output stage transistors. That power is simply the tar-

get line power used in Equation 2 plus the power lost in the

matching elements (RM). In the examples here, a perfect

match is targeted giving the same power in the matching

elements as in the load. The output stage power is then set

by Equation 11.

P OUT

VCC * 2PL

(11)

The total amplifier power is then:

PTOT + Iq

VCC

)

VCC * 2PL

(12)

For the ADSL CPE upstream driver design of Figure 5, the

peak current is 128mA for a signal that requires a crest fac-

tor of 5.33 with a target line power of 13dBm into 100â¦

(20mW). With a typical quiescent current of 18mA and a

nominal supply voltage of +12V, the total internal power

dissipation for the solution of Figure 5 will be:

(13)

PTOT

18mA(12V)

)

128mA

5.33

(12V)

2(20mW)

464mW

DESIGN-IN TOOLS

DEMONSTRATION FIXTURES

Two printed circuit boards (PCBs) are available to assist

in the initial evaluation of circuit performance using the

OPA2674 in its two package options. Both of these are of-

fered free of charge as unpopulated PCBs, delivered with

a userâs guide. The summary information for these fixtures

is shown in Table 2.

Table 2. Demonstration Fixtures by Package

PRODUCT

OPA2674ID

OPA2674I-14D

PACKAGE

SO-8

SO-14

ORDERING

NUMBER

DEM-OPA-SO-2A

DEM-OPA-SO-2D

LITERATURE

NUMBER

SBOU003

SBOU002

The demonstration fixtures can be requested at the Texas

Instruments web site (www.ti.com) through the OPA2674

product folder.

MACROMODELS AND APPLICATIONS

SUPPORT

Computer simulation of circuit performance using SPICE

is often useful when analyzing the performance of analog

circuits and systems. This is particularly true for video and

RF amplifier circuits where parasitic capacitance and in-

ductance can have a major effect on circuit performance.

A SPICE model for the OPA2674 is available through the

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