ssm2275s Analog Devices, Inc., ssm2275s Datasheet - Page 14

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

SSM2275/SSM2475
SPICE Macro-model
The SPICE macro-model for the SSM2275 is shown in Listing
1 on the following page. This model is based on typical values
for the device and can be downloaded from Analog Devices’
Internet site at www.analog.com. The model uses a common
emitter output stage to provide rail-to-rail performance. A resis-
tor and dc voltage source, in series with the collector, accurately
portray output dropout voltage versus output current. The
VCMH and VCML sources set the upper and lower limits of
the input common mode voltage range. Both are set up as a
function of the supply voltage to mimic the varying common
mode range with supply voltage. The EOS voltage source estab-
lishes the offset voltage and is also used to create the common-
mode rejection and power supply rejection characteristics for
the model.
1
2
3
4
5
6
7
8
LL
DL
CK
DR
DGND
V
LR
VBR
L
SERIAL
SERIAL
18-BIT
18-BIT
18-BIT
18-BIT
DAC
DAC
REG.
REG.
Figure 42. A Smoothing Filter for an 18-Bit Stereo DAC
AD1868
V
V
REF
REF
AGND
VOL
VOR
VBL
V
S
+5V SUPPLY
16
15
14
13
12
11
10
9
7.68k
7.68k
330pF
330pF
–14–
A secondary pole section is also set up to vary the gain band-
width product and phase margin of the model based on the
supply voltage. The H1 and VR1 sources set up an equivalent
resistor that is linearly varied with supply voltage. This equiva-
lent resistance, in parallel with C2, creates the secondary pole.
G2 is also linearly varied to increase the GBW at higher supply
voltages. With a supply voltage of 5 V, the gain bandwidth
product is 6.3 MHz with a 47 degree phase margin. At a 30 V
supply voltage, the GBW product moves out to 7.5 MHz with
48 phase margin.
The broadband input referred voltage noise for the model is
6.8 nV/√Hz. Flicker noise characteristics are also accurately
modeled with the 1/f corner frequency set through the KF and
AF terms in the input stage transistors. Finally, a voltage-con-
trolled current source, GSY, is used to model the amplifier’s
supply current versus supply voltage characteristics.
9.76k
9.76k
SSM2275
7.68k
7.68k
1/2
3
2
6
5
SSM2275
1/2
4
8
100pF
100pF
1
7
220 F
220 F
47k
47k
LEFT
CHANNEL
OUTPUT
RIGHT
CHANNEL
OUTPUT
REV. A