OP250 Datasheet, PDF (12/16 Pages) Analog Devices – CMOS Single-Supply Rail-to-Rail Input/Output Operational Amplifiers

OP250/OP450
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
V_IN
100mV p-p
OP250
R_S
5
C_S
1F
V_OUT
C_L
47nF
Figure 33. Schematic for Using a Snubber Network
Table I. Snubber Network for Large Capacitive Loads
Load Capacitance (C_L)
1 nF
10 nF
100 nF
Snubber Network (RS, CS)
60 Ω, 30 nF
20 Ω, 1 µF
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.
V_IN = 100mV_p-p @ 100kHz
C_L = 1nF
R_L = 10k
50mV
2µs
Figure 34. Output of OP250 without Snubber Network
C_L = 1nF
R_L = 10k
V_IN = 100mV_p-p @ 100kHz
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.
R2
10k
+5V
C1 ²
22 F _{3 A1}
1
V_IN
R1
10k
A1, A2 = 1/2 OP250
GAIN = ^R3
R2
R10
10k
SET: R7, R10, R11 = R2
SET: R6, R12, R13 = R3
R3
10k
2
1
3 ^A2
R5
50
R6
10k
R7
10k
+5V
+12V
6
7
A1 ₅
R8
100k
R9 C2
100k
1F
R11
10k
R12
10k
6
R14
7
50
5 ^A2 _R13
10k
C3
47 F
V_O1
R_L
600
C4
47µF
V_O2
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
= ^VOUT
V_IN
=
R3
R2
(5)
Where: V_OUT = V_O1 – V_O2,
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.
50mV
2µs
Figure 35. Output of OP250 with Snubber Network
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