DRV1101 Datasheet, PDF (4/8 Pages) Burr-Brown (TI) – HIGH POWER DIFFERENTIAL LINE DRIVER

APPLICATIONS INFORMATION
INTERNAL BLOCK DIAGRAM
Out+
The DRV1101 is a true differential input to differential
output fixed gain amplifier. Operating on a single +5V
V_DD/2
power supply, it provides an internally fixed differential
gain of +3V/V and a common-mode gain of +1V/V from the
Out–
input to output. Fabricated on an advanced CMOS process,
it offers very high input impedance along with a low imped-
V_DD/2
ance 230mA output drive. Figure 1 shows a simplified
internal block diagram.
Load
0V
V_P
V_P
V_P
V_P
In+
Preamp
In–
Buffer
Out+
Out–
FIGURE 1. Simplified DRV1101 Internal Block Diagram.
The DRV1101 should be operated with the inputs centered
at V_DD / 2. This will place the output differential voltage
centered at V_DD/ 2 for maximum swing and lowest distor-
tion. Purely differential input signals will produce a purely
differential output signal. A single ended input signal, ap-
plied to one input of the DRV1101, with the other input at
a fixed voltage, will produce both a differential and com-
mon-mode output signal. This is an acceptable mode of
operation when the DRV1101 is driving an element with
good common-mode rejection (such as a transformer).
DIFFERENTIAL OUTPUT VOLTAGE AND POWER
Applying the balanced differential output voltage of the
DRV1101 to a load between the outputs will produce a peak-
to-peak voltage swing that is twice the swing of each
individual output. This is illustrated in Figure 2 where the
common-mode voltage is V_DD / 2. For a load connected
between the outputs, the only voltage that matters is the
differential voltage between the two outputs—the common-
mode voltage does not produce any load current in this case.
The peak power that the DRV1101 can deliver into a differ-
ential load is V_P2/R_L. The peak voltage (Vp) equals 1/2 of the
peak-to-peak voltage (Vp-p). Squaring 1/2 of the Vp-p and
dividing by the load impedance will give the peak power. For
FIGURE 2. DRV1101 Single Ended and Differential Output
Waveforms.
example, the specifications show that on +5V supply the
DRV1101 will deliver 6.0Vp-p into 15Ω. The peak load
power under this condition is (6.0Vp-p/2)²/15Ω = 600mW.
POWER SUPPLY
The DRV1101 is designed for operation on a single +5V
supply. For loads > 200Ω, each output will swing rail to rail.
This gives a peak-to-peak differential output swing that is
approximately = 2 • V_DD. For best distortion performance,
the power supply should be decoupled to a good ground
plane immediately adjacent to the package with a 0.1µF
capacitor. In addition, a larger electrolytic supply decoupling
capacitor (6.8µF) should be near the package but can be
shared among multiple devices.
DIGITAL SUBSCRIBER LINE APPLICATIONS
The DRV1101 is designed for the high power, low distor-
tion, requirements of a twisted pair driver in digital commu-
nications applications. These include ADSL (Asymmetrical
Digital Subscriber Lines), and RADSL (Rate adaptive ADSL).
Figure 3 shows a typical transformer coupled xDSL line
driver configuration.
The DRV1101 is recommended as the upstream driver (CPE
equipment) for ADSL G.Lite systems. These system require
an rms line power of 10dBm with a voltage crest factor of
5.3 (crest factor is the ratio of peak to rms voltage). A
voltage crest factor of 5.3 is equivalent to a power crest
factor of about 15dB. Therefore, the peak power required at
the line for G.Lite is 25dBm. Using the basic circuit shown
in Figure 3, DRV1101 will provide this power to the line
with very low distortion.
®
DRV1101
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