ADA4075-2ACPZ-RL Analog Devices Inc, ADA4075-2ACPZ-RL Datasheet - Page 18

• Manufacturer Part Number: ADA4075-2ACPZ-RL
• Description: Low Noise/Power 36V OpAmp
• Manufacturer: Analog Devices Inc
• Series: iPolar®r

Specifications of ADA4075-2ACPZ-RL

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Slew Rate: 12 V/µs
• Gain Bandwidth Product: 6.5MHz
• Current - Input Bias: 30nA
• Voltage - Input Offset: 300µV
• Current - Supply: 1.8mA
• Current - Output / Channel: 40mA
• Voltage - Supply, Single/dual (±): ±4.5 V ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADA4075-2
BALANCED LINE DRIVER
The circuit of Figure 67 shows a balanced line driver designed
for audio use. Such drivers are intended to mimic an output
transformer in operation, whereby the common-mode voltage
can be impressed by the load. Furthermore, either output can be
shorted to ground in single-ended applications without affecting
the overall operation.
Circuits of this type use positive and negative feedback to obtain a
high common-mode output impedance, and they are somewhat
notorious for component sensitivity and susceptibility to latch-up.
This circuit uses several techniques to avoid spurious behavior.
First, the 4-op-amp arrangement ensures that the input impedance
is load independent (the input impedance can become negative
with some configurations). Note that the output op amps are
packaged with the input op amps to maximize drive capability.
Second, the positive feedback is ac-coupled by C2 and C3, which
eliminates the need for offset trim. Because the circuit is ac-coupled
at the input, these capacitors do not have significant dc voltage
across them, thus tantalum types of capacitors can be used.
10µF
10kΩ
NOTES
1. ALL RESISTORS SHOULD HAVE 1% TOLERANCE.
2. A1/A2 IN SAME PACKAGE; A3/A4 IN SAME PACKAGE.
C1
R1
IN
R2
4.7kΩ
ADA4075-2
ADA4075-2
4.7kΩ
4.7kΩ
1/2
R18
R3
1/2
A1
50pF
C4
A3
Figure 67. Balanced Line Driver
4.7kΩ
Rev. A | Page 18 of 24
4.7kΩ
4.7kΩ
R4
4.7kΩ
R10
R15
R6
SYMMETRY
TRIM
FEEDBACK
TRIM
R11
250Ω
R7
250Ω
ADA4075-2
ADA4075-2
4.7kΩ
50pF
C5
R5
50pF
Finally, even with these precautions, it is vital that the positive
feedback be accurately controlled. This is partly achieved by
using 1% resistors. In addition, the following setup procedure
ensures that the positive feedback does not become excessive:
1.
2.
3.
The overall gain of the driver is equal to 2, which provides an
extra 6 dB of headroom in balanced differential mode. The
output noise is about −109 dBV in a 20 kHz bandwidth.
100Ω
C6
R16
1/2
1/2
4.7kΩ
R12
A2
A4
100Ω
Set R11 to its midposition (or short the ends together,
whichever is easier) and temporarily short the negative
output to ground.
Apply a 10 V p-p sine wave at approximately 1 kHz to the
input and adjust R7 to provide 930 mV p-p at TEST (see
Figure 67).
Remove the short from the negative output (and across
R11, if used) and adjust R11 until the output waveforms
are symmetric.
R8
TEST
4.7kΩ
100Ω
R9
R14
100Ω
R13
4.7kΩ
R17
C2
10µF
C3
10µF
OUT+
OUT–