ssm2275s Analog Devices, Inc., ssm2275s Datasheet - Page 12

• Manufacturer Part Number: ssm2275s
• Description: Rail-to-rail Output Audio Amplifiers
• Manufacturer: Analog Devices, Inc.

SSM2275/SSM2475
Capacitive Loading
The output of the SSM2275/SSM2475 can tolerate a degree of
capacitive loading. However, under certain conditions, a heavy
capacitive load could create excess phase shift at the output and
put the device into oscillation. The degree of capacitive loading
is dependent on the gain of the amplifier. At unity gain, the am-
plifier could become unstable at loads greater than 600 pF. At
gain greater than unity, the amplifier can handle a higher degree
of capacitive load without oscillating. Figure 35 shows how to
configure the device to prevent oscillations from occurring.
R
parallel combination of R
ting a minimum C
eliminate any oscillation problems from any sized capacitive
load. The low-pass frequency is determined by:
With R
with a 210 kHz bandwidth that can be used with any capacitive
load. If the amplifier is being used in a noninverting unity gain
configuration and R
If the offset voltage can be tolerated at the output, R
replaced by a short and C
typical input bias current of 200 nA and R
crease in offset voltage would be 10 mV. This configuration will
stabilize the amplifier under all capacitive loads.
Single Supply Differential Line Driver
Figure 36 shows a single supply differential line driver circuit
that can drive a 600
The design mimics the performance of a fully balanced trans-
former 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 applications
without changing the circuit gain of 1.
R13 and R14 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 minimum input impedance of the cir-
cuit as seen from V
B
Figure 35. Configurations for Driving Heavy Capacitive
Loads
V
should be at least 50 k . To minimize offset voltage, the
IN
INVERTING GAIN AMPLIFIER
FB
50k
R
R
B
= 50 k and C
I
SSM2275
C
R
FB
FB
F
IN
R
I
of 15 pF bandlimits the amplifier enough to
f
is omitted, C
IN
is:
3
dB
load with less than 0.001% distortion.
C
L
F
FB
FB
V
= 15 pF, this results in an amplifier
R
OUT
2
and R
1
can be removed entirely. With the
R C
R
1
V
FB
5
I
FB
IN
should be equal to R
NONINVERTING GAIN AMPLIFIER
should be at least 100 pF.
F
R
50k
R
R
3
B
I
B
R
= 50 k , the in-
SSM2275
7
C
R
FB
FB
R
11
FB
C
can be
L
B
. Set-
V
OUT
(6)
(7)
–12–
For the values given in Figure 36, R
the circuit will provide a balanced output down to dc, otherwise
the –3 dB corner for the input frequency is set by:
The circuit can also be configured to provide additional gain if
desired. The gain of the circuit is:
where V
R2 = R4 = R6 = R8
Figure 37 shows the THD+N versus frequency response of the
circuit while driving a 600
Figure 37. THD+N vs. Frequency of Differential Line Driver
10 F
V
IN
C2
Figure 36. A Low Noise, Single Supply Differential
Line Driver
0.0001
0.001
OUT
10 F
0.01
100k
C1*
100k
0.1
R14
R13
20
C1* IS OPTIONAL
= V
+12V
10k
V
R
SY
R11
L
= 600
O1
= 12V
SSM2475-C
– V
f
+5V
A
100
10k
O2
3
R12
V
dB
, R1 = R3 = R5 = R7 and,
V
V
2
OUT
FREQUENCY – Hz
load at 1 V rms.
IN
10k
R C
10k
R1
10k
1
10k
R3
IN
R7
R5
2(R2)
IN
R1
L
1k
SSM2475-A
= 5 k . With C1 omitted
SSM2475-B
10k
+12V
10k
+12V
33pF
33pF
C3
R2
C4
R8
10k
R4
50
R10
10 F
50
C4
R9
R6
10k
C3
10k
10 F
20k
REV. A
V
V
(8)
(9)
01
02