THS6214IPWPR datasheet(27/41 Pages) TI

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TOTAL DRIVER POWER FOR xDSL

=21mA(24V)+

TOT

5.6

159mA

(24V)

2(115mW)=955mW

OUTPUT CURRENT AND VOLTAGE

AVG

OUT

(13)

TOT

(14)

THS6214

www.ti.com ....................................................................................................................................................................................................... SBOS431 – MAY 2009

With a typical quiescent current of 21mA and a

APPLICATIONS

nominal supply voltage of ±12V, the total internal

power dissipation for the solution of Figure 82 is:

The total internal power dissipation for the THS6214

in an xDSL line driver application is the sum of the

quiescent power and the output stage power. The

(15)

THS6214

holds

relatively

constant

quiescent

current

versus

supply

voltage—giving

power

contribution that is simply the quiescent current times

the supply voltage used (the supply voltage is greater

The THS6214 provides output voltage and current

than the solution given in Equation 11). The total

capabilities that are unsurpassed in a low-cost, dual

output stage power can be computed with reference

monolithic op amp. Under no-load conditions at

to Figure 86.

+25°C, the output voltage typically swings closer than

1.1V to either supply rail; tested at +25°C, the swing

limit is within 1.4V of either rail into a 100

Ω differential

load. Into a 25

Ω load (the minimum tested load), the

amplifier delivers more than ±408mA continuous and

greater than ±1A peak output current.

The specifications described above, though familiar in

the industry, consider voltage and current limits

separately. In many applications, it is the voltage

times current (or V-I product) that is more relevant to

circuit operation. Refer to the Output Voltage and

Current Limitations plot (Figure 14) in the Typical

Characteristics. The X- and Y-axes of this graph

show the zero-voltage output current limit and the

zero-current output voltage limit, respectively. The

Figure 86. Output Stage Power Model

four quadrants give a more detailed view of the

THS6214 output drive capabilities, noting that the

graph is bounded by a safe operating area of 1W

The two output stages used to drive the load of

maximum internal power dissipation (in this case, for

Figure 83 can be seen as an H-Bridge in Figure 86.

one channel only). Superimposing resistor load lines

The average current drawn from the supply into this

onto the plot shows that the THS6214 can drive

H-Bridge and load is the peak current in the load

±10.9V into 100

Ω or ±10.5V into 50Ω without

given by Equation 9 divided by the crest factor (CF)

exceeding

the

output

capabilities

the

for the xDSL modulation. This total power from the

dissipation limit. A 100

Ω load line (the standard test

supply is then reduced by the power in RT, leaving

circuit load) shows the full ±12V output swing

the power dissipated internal to the drivers in the four

capability, as shown in the Electrical Characteristics

output stage transistors. That power is simply the

tables. The minimum specified output voltage and

target line power used in Equation 4 plus the power

current over temperature are set by worst-case

lost in the matching elements (RM). In the following

simulations at the cold temperature extreme. Only at

examples, a perfect match is targeted giving the

cold startup do the output current and voltage

same power in the matching elements as in the load.

decrease to the numbers shown in the Electrical

The output stage power is then set by Equation 13.

Characteristics tables. As the output transistors

deliver power, the junction temperature increases,

decreasing the VBEs (increasing the available output

voltage swing), and increasing the current gains

The total amplifier power is then:

(increasing

the

available

output

current).

steady-state operation, the available output voltage

and current are always greater than that shown in the

over-temperature specifications, because the output

For the ADSL CO driver design of Figure 82, the

stage junction temperatures are higher than the

peak current is 159mA for a signal that requires a

minimum specified operating ambient temperature.

crest factor of 5.6 with a target line power of 20.5dBm

To maintain maximum output stage linearity, no

into a 100

Ω load (115mW).

output

short-circuit

protection

provided.

This

absence of short-circuit protection is normally not a

problem

because

most

applications

include

series-matching resistor at the output that limits the

internal power dissipation if the output side of this

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