DRV134 Datasheet, PDF (16/30 Pages) Burr-Brown (TI) – AUDIO BALANCED LINE DRIVERS

DRV134, DRV135
SBOS094B – JANUARY 1998 – REVISED DECEMBER 2014
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Typical Application (continued)
9.2.1.2 Detailed Design Procedure
The dBu is a common unit of measurement for input sensitivity and output level of professional audio equipment.
A 0 dBu signal dissipates 1 mW into a 600-Ω resistive load; therefore, a 0 dBu signal corresponds to
approximately 0.775 V_RMS. Equation 1 shows the relationship between the signal level in dBu (denoted by L_u)
and the signal level in V_RMS (denoted by x).
L_u
20
log₁₀
¨§
©
x
0.775
¸·
¹
(1)
For this design, the single ended input signal of 22.2 dBu corresponds to 9.98 V_RMS as shown in Equation 2.
V_IN
0
.775
¨¨©§
10
L_u
20
¸¸¹·
9.98 V_RMS
(2)
Given that the system must accommodate for 22.2 dBu signals with up to 1.5 of peak to RMS ratio, the
maximum peak input signal is 14.97 V_PEAK as calculated in Equation 3.
  V_{IN_ PEAK} 1.5 9.98 14.97 V_PEAK
(3)
The DRV134 is chosen to convert the single ended input signal into a differential signal and the outputs of the
DRV134 will be connected to one end of the 500 ft cable. In order to prevent clipping and distortion of the input
signal, the power supply rails for the DRV134 are chosen as 3 V above and below the peak calculated in
Equation 3. The 3 V margin is derived from the output voltage swing specification given in the Electrical
Characteristics table. The supplies selected are 18 V for V+ and –18 V for V–.
Finally, the INA137 is used at the end of the 500 ft cable in order to convert the differential signal output of the
DRV134 into a single ended signal that is 0 dB with respect to the input signal.
Figure 30 shows the system diagram.
+18V
+18V
1µF
1µF
Test Point
or
V_IN
6
+V_O
4
7
8
–In
2
7
5
DRV134
1
2
R_L
INA137
6
V_OUT
+In
1
3
5
–V_O
3
4
R₁
R₂
1µF
1µF
–18V
–18V
Figure 30. Diagram of System Based on DRV134 and INA137
16
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