OPA2614ID Datasheet, PDF(20/34 Page) Texas Instruments – Dual, High Gain Bandwidth, High Output Current Operational Amplifier with Current Limit

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OPA2614ID Datasheet, PDF (20/34 Pages) Texas Instruments – Dual, High Gain Bandwidth, High Output Current Operational Amplifier with Current Limit

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OPA2614

SBOS305D â JUNE 2004 â REVISED AUGUST 2008

With VLPP as defined in Equation 8, and RM as defined in

Equation 4 and shown in Figure 11.

1:n

Vpp =

2VLpp

VLpp

Figure 11. Driver Peak Output Voltage

With the previous information available, it is now possible

to select a supply voltage and the turns ratio desired for the

transformer as well as calculate the headroom for the

OPA2614.

The model (shown in Figure 12) can be described with the

following set of equations:

1. First, as available output swing:

VPP + VCC * (V1 ) V2) * IP (R1 ) R2) (11)

2. Or as required supply voltage:

VCC + VPP ) (V1 ) V2) ) IP (R1 ) R2) (12)

The minimum supply voltage for a power and load

requirement is given by Equation 11.

+VCC

Figure 12. Line Driver Headroom Model

V1, V2, R1, and R2 are given in Table 1 for both +12V and

+5V operation.

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Table 1. Line Driver Headroom Model Values

+5V

1.0V

2â¦

1.0V

5.5â¦

+12V

1.0V

2â¦

1.0V

5.5â¦

TOTAL DRIVER POWER FOR xDSL

APPLICATIONS

The total internal power dissipation for the OPA2614 in an

xDSL line driver application will be the sum of the

quiescent power and the output stage power. The

OPA2614 holds a relatively constant quiescent current

versus supply voltageâgiving a power contribution that is

simply the quiescent current times the supply voltage used

(the supply voltage will be greater than the solution given

in Equation 12). The total output stage power may be

computed with reference to Figure 13.

+VCC

IAVG

Figure 13. Output Stage Power Model

The two output stages used to drive the load of Figure 11

can be seen as an H-Bridge in Figure 13. The average

current drawn from the supply into this H-Bridge and load

will be the peak current in the load given by Equation 10

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 target line power used in Equation 5 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 13.

P OUT

VCC * 2PL

(13)

The total amplifier power is then:

PTOT + Iq

VCC

)

VCC * 2PL

(14)

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