THS6204IPWPR datasheet(27/43 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

´ CC

(14)

THS6204

www.ti.com ................................................................................................................................................... SBOS416C – OCTOBER 2007 – REVISED APRIL 2009

APPLICATIONS

(15)

The total internal power dissipation for the THS6204

in an xDSL line driver application will be the sum of

the quiescent power and the output stage power. The

THS6204

holds

relatively

constant

quiescent

The THS6204 provides output voltage and current

current

versus

supply

voltage—giving

power

capabilities that are unsurpassed in a low-cost dual

contribution that is simply the quiescent current times

monolithic op amp. Under no-load conditions at

the supply voltage used (the supply voltage will be

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

greater than the solution given in Equation 11). The

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

total output stage power may be computed with

is within 1.4V of either rail into a 100

Ω differential

reference to Figure 86.

load. Into a 25

Ω load (the minimum tested load), it

delivers more than ±408mA continuous and > ±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

four quadrants give a more detailed view of the

THS6204 output drive capabilities, noting that the

graph is bounded by a safe operating area of 1W

Figure 86. Output Stage Power Model

maximum internal power dissipation (in this case for 1

channel only). Superimposing resistor load lines onto

the plot shows that the THS6204 can drive ±10.9V

The two output stages used to drive the load of

into 100

Ω or ±10.5V into 50Ω without exceeding the

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

output capabilities or the 1W dissipation limit. A 100

Ω

The average current drawn from the supply into this

load line (the standard test circuit load) shows the full

H-Bridge and load will be the peak current in the load

±12V output swing capability, as shown in the

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

Electrical

Characteristics

tables.

The

minimum

for the xDSL modulation. This total power from the

specified output voltage and current over temperature

supply is then reduced by the power in RT to leave

are set by worst-case simulations at the cold

the power dissipated internal to the drivers in the four

temperature extreme. Only at cold startup will the

output stage transistors. That power is simply the

output current and voltage decrease to the numbers

target line power used in Equation 4 plus the power

shown in the Electrical Characteristics tables. As the

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

output

transistors

deliver

power,

the

junction

here, a perfect match is targeted giving the same

temperatures

increases,

decreasing

the

VBEs

power in the matching elements as in the load. The

(increasing the available output voltage swing), and

output stage power is then set by Equation 12.

increasing the current gains (increasing the available

output

current).

steady-state

operation,

the

available output voltage and current will always be

greater than that shown in the over-temperature

The total amplifier power is then:

specifications,

since

the

output

stage

junction

temperatures will be higher than the minimum

specified operating ambient. To maintain maximum

output

stage

linearity,

output

short-circuit

For the ADSL CO driver design of Figure 82, the

protection is provided. This is normally not a problem

peak current is 159mA for a signal that requires a

because most applications include a series-matching

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

resistor at the output that limits the internal power

into 100

Ω (115mW). With a typical quiescent current

dissipation if the output side of this resistor is shorted

of 21mA and a nominal supply voltage of ±12V, the

to ground. However, shorting the output pin directly to

total internal power dissipation for the solution of

the

adjacent

positive

power-supply

(24-pin

Figure 82 will be:

package), will in most cases, destroy the amplifier. If

additional short-circuit protection is required, a small

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