OP250/OP450

REV. 0

–12–

be connected from the output to ground in parallel with the ca-

pacitive load as shown in Figure 33. The proper snubber net-

work on the output can significantly reduce output overshoot,

although it will not increase the bandwidth. Table I shows some

snubber network values for a given capacitive load. In practice,

these values are best determined empirically based on the exact

capacitive load for the application.

+5V

5

100mV p-p

OP250

47nF

1 F

Figure 33. Schematic for Using a Snubber Network

Table I. Snubber Network for Large Capacitive Loads

Snubber Network (RS, CS)

1 nF

60

Ω, 30 nF

10 nF

20

Ω, 1 µF

100 nF

3

Ω, 10 µF

Figure 34 shows the output of an OP250 in a unity gain configu-

ration with a 1 nF capacitive load. Figure 35 shows the improve-

ment in the output response with the snubber network added.

2µs

50mV

Figure 34. Output of OP250 without Snubber Network

2µs

50mV

Figure 35. Output of OP250 with Snubber Network

For more information on methods to drive a capacitive load with

an op amp, please refer to the Ask the Applications Engineer ar-

ticle in Analog Dialogue, Vol. 31, Number 2, 1997.

Single Supply Differential Line Driver

Figure 36 shows a single supply differential line driver circuit

that can drive a 600

Ω load with less than 0.1% distortion. The

design uses an OP450 to mimic the performance of a fully bal-

anced transformer based solution. However, this design occupies

much less board space while maintaining low distortion and can

operate down to dc. Like the transformer based design, either

output can be shorted to ground for unbalanced line driver ap-

plications without changing the circuit gain of 1.

600

C1

22 F

A2

7

6

5

3

1

2

A1

+5V

R1

10k

R2

10k

R11

10k

R7

10k

6

7

5

A1

+12V

+5V

R8

100k

R9

100k

C2

1 F

R12

10k

R14

50

A2

1

2

3

R3

10k

R6

10k

R13

10k

C3

47 F

C4

47µF

A1, A2 = 1/2 OP250

GAIN = R3

R2

SET: R7, R10, R11 = R2

SET: R6, R12, R13 = R3

R10

10k

R5

50

Figure 36. A Low Noise, Single Supply Differential Line Driver

R8 and R9 set up the common mode output voltage equal to

half of the supply voltage. C1 is used to couple the input signal

and can be omitted if the input’s dc voltage is equal to half of

the supply voltage.

The circuit can also be configured to provide additional gain if

desired. The gain of the circuit is:

A

V

V

R

R

V

OUT

IN

==

3

2

(5)

R2 = R7 = R10 = R11 and,

R3 = R6 = R12 = R13

Multimedia Headphone Amplifier

Because of its large output drive, the OP250 makes an excellent

headphone amplifier, as illustrated in Figure 37. Its low supply

operation and rail-to-rail inputs and outputs can maximize out-

put signal swing on a single +5 V supply. In Figure 37, the am-

plifier inputs are biased halfway between the supply voltages,

which in this application is 2.5 V. A 10

µF capacitor prevents

power supply noise from contaminating the audio signal.