SSM2211x Analog Devices, SSM2211x Datasheet - Page 13

• Manufacturer Part Number: SSM2211x
• Description: Low Distortion 1.5 Watt Audio Power Amplifier
• Manufacturer: Analog Devices

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REV. 0
will produce a high pass filter with a corner frequency given by
Equation 4. For a speaker load of 8
of 470 F, this results in a –3 dB frequency of 42 Hz.
Because the power of a single ended output is one quarter that of a
bridged output, both speakers together would still be half as loud
(–6 dB SPL) as a single speaker driven with a bridged output.
The polarity of the speakers is important, as each output is 180
out of phase with the other. By connecting the minus terminal
of Speaker 1 to Pin 5, and the plus terminal of Speaker 2 to
Pin 8, proper speaker phase can be established.
The maximum power dissipation of the device can be found by
doubling Equation 11, assuming both loads are equal. If the
loads are different, use Equation 11 to find the power dissipa-
tion caused by each load, then take the sum to find the total
power dissipated by the SSM2211.
Evaluation Board
An evaluation board for the SSM2211 is available. Contact
your local sales representative or call 1-800-ANALOGD for
more information.
The voltage gain of the SSM2211 is given by Equation 20 below:
If desired, the input signal may be attenuated by turning the
10 k potentiometer in the CW direction. C
common mode voltage (V+/2) present at Pin 2 and 3. With
V+ = 5 V, there is +2.5 V common-mode voltage present at
both output terminals V
CAUTION: The ground lead of the oscilloscope probe, or any
other instrument used to measure the output signal, must not be
connected to either output, as this would short out one of the
amplifier’s outputs and possibly damage the device.
A safe method of displaying the differential output signal using a
grounded scope is shown in Figure 48. Simply connect the Chan-
nel A probe to V
V
Most multichannel oscilloscopes have this feature built in. If you
O1
AUDIO
INPUT
VOLUME
20k
post, invert Channel B and add the two channels together.
SHUTDOWN
POT.
Figure 47. Evaluation Board Schematic
CW
ON
O2
C
1 f
terminal post, connect the Channel B probe to
IN
+
20k
R
O1
IN
A
51k
V
and V
R1
2
1
2
3
4
O2
SSM2211
R
R
0.1 F
20k
as well.
IN
R
F
C
V+
F
1
6
and a coupling capacitor
7
+
8
5
10 F
IN
C
2
J1
J2
isolates the input
0.1 F
C
1
1W 8
R
L
V
V
02
01
(20)
–13–
must connect the ground lead of the test instrument to either out-
put signal pins, a power line isolation transformer must be used
to isolate the instrument ground from power supply ground.
Recall that V
V = 2.8 V rms, or 8 V p-p. If the available input signal is 1.4 V
rms or more, use the board as is, with R
gain is needed, increase the value of R
When you have determined the closed-loop gain required by
your source level, and can develop 1 W across the 8
sistor with the normal input signal level, replace the resistor
with your speaker. Your speaker may be connected across the
V
8
should be connected to the (+) terminal of the speaker.
Figure 48. Using an Oscilloscope to Display the Bridged
Output Voltage
To use the SSM2211 in a single ended output configuration,
replace J1 and J2 jumpers with electrolytic capacitors of a suit-
able value, with the NEGATIVE terminals to the output termi-
nals V
to ground. Note that the maximum output power is reduced to
250 mW, one quarter of the rated maximum, due to the maxi-
mum swing in the non-bridged mode being one-half, and power
being proportional to the square of the voltage. For frequency
response down 3 dB at 100 Hz, a 200 F capacitor is required
with 8
The SSM2211 evaluation board also comes with a SHUT-
DOWN switch which allows the user to switch between ON
(normal operation) and the power conserving shutdown mode.
Printed Circuit Board Layout Consideration
All surface mount packages rely on the traces of the PC board
to conduct heat away from the package.
In standard packages, the dominant component of the heat re-
sistance path is the plastic between the die attach pad and the
individual leads. In typical thermally enhanced packages, one or
more of the leads are fused to the die attach pad, significantly
decreasing this component. To make the improvement mean-
ingful, however, a significant copper area on the PCB must be
attached to these fused pins.
The patented Thermal Coastline lead frame design used in the
SSM2211 (Figure 49) uniformly minimizes the value of the
dominant portion of the thermal resistance. It ensures that heat
is conducted away by all pins of the package. This yields a very
low, 98 C/W, thermal resistance for an SO-8 package, without
any special board layer requirements, relying on the normal
traces connected to the leads. The thermal resistance can be de-
creased by approximately an additional 10% by attaching a few
O1
SSM2211
and V
load resistor is removed. For no phase inversion, V
O1
and V
speakers.
O2
5
8
COMMON
posts for bridged mode operation only after the
MODE
2.5V
O2
. The single ended loads may then be returned
P
R , so for P
8
1W
GND
V
V
O2
O1
O
PROBES
= 1 W and R
F
to obtain the desired gain.
F
= R
I
CH A
CH B
SSM2211
= 20 k . If more
L
OSCILLOSCOPE
= 8 ,
INV. ON
CH B
load re-
O2
DISPLAY
A+B