10

®

DRV134, 135

SIGNAL BALANCE RATIO

Signal balance ratio (SBR) measures the symmetry of the

output signals under loaded conditions. To measure SBR an

input signal is applied and the outputs are summed as shown

is exactly equal and opposite. However, an error signal

results from any imbalance in the outputs. This error is

quantified by SBR. The impedances of the DRV134’s out

put stages are closely matched by laser trimming to mini-

mize SBR errors. In an application, SBR also depends on the

balance of the load network.

SINGLE-ENDED OPERATION

The DRV134 can be operated in single-ended mode without

degrading output drive capability. Single-ended operation

requires that the unused side of the output pair be grounded

Gain remains +6dB. Grounding the negative outputs as

shown in Figure 6 results in a noninverted output signal

(G = +2) while grounding the positive outputs gives an

inverted output signal (G = –2).

FIGURE 6. Typical Single-Ended Application.

FIGURE 5. Signal Balance Ratio Test Circuit.

600

Ω

V

V

IN

V+

V–

DRV134

8

1

7

2

G = +6dB

4

5

6

3

For best rejection of line noise and hum differential mode

operation is recommended. However, single-ended perfor-

mance is adequate for many applications. In general single-

ended performance is comparable to differential mode (see

THD+N typical performance curves), but the common-

mode and noise rejection inherent in balanced-pair systems

is lost.

CABLE

The DRV134 is capable of driving large signals into 600

Ω

loads over long cables. Low impedance shielded audio

cables such as the standard Belden 8451 or 9452 (or similar)

are recommended, especially in applications where long

cable lengths are required.

THERMAL PERFORMANCE

The DRV134 and DRV135 have robust output drive capa-

bility and excellent performance over temperature. In most

applications there is no significant difference between the

DIP, SOL-16, and SO-8 packages. However, for applica-

tions with extreme temperature and load conditions, the

SOL-16 (DRV134UA) or DIP (DRV134PA) packages are

recommended. Under these conditions, such as loads greater

than 600

Ω or very long cables, performance may be de-

graded in the SO-8 (DRV135UA) package.

LAYOUT CONSIDERATIONS

A driver/receiver balanced-pair (such as the DRV134 and

INA137) rejects the voltage differences between the grounds

at each end of the cable, which can be caused by ground

currents, supply variations, etc. In addition to proper bypass-

ing, the suggestions below should be followed to achieve

optimal OCMR and noise rejection.

• The DRV134 input should be driven by a low impedance

source such as an op amp or buffer.

• As is the case for any single-ended system, the source’s

common should be connected as close as possible to the

DRV134’s ground. Any ground offset errors in the source

will degrade system performance.

• Symmetry on the outputs should be maintained.

• Shielded twisted-pair cable is recommended for all appli-

cations. Physical balance in signal wiring should be main-

tained. Capacitive differences due to varying wire lengths

may result in unequal noise pickup between the pair and

degrade OCMR. Follow industry practices for proper sys-

tem grounding of the cables.

V

OUT

V

IN

(

)

600

Ω

300

300

V

OUT

SBR = –20 Log

at f = 1kHz

V

+V

O

–V

O

DRV134

1

µF

+18V

6

8

1

7

2

1

µF

–18V

Gnd

5

4

3

NOTE: (1) Matched to 0.1%.