SSM2211_02 データシートの表示（PDF） - Analog Devices
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SSM2211_02 Datasheet PDF : 16 Pages
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SSM2211
0.35
0.30
VDD = 5V
RL = 4⍀
0.25
0.20
0.15
0.10
0.05
RL = 8⍀
RL = 16⍀
0
0
0.1
0.2
0.3
0.4
OUTPUT POWER – W
Figure 5. Power Dissipation vs. Single Ended Output
Power with (VDD = 5 V)
The maximum power dissipation for a single ended output is:
2
PDISS ,MAX
=
VDD
2 p 2RL
(11)
Output Voltage Headroom
The outputs of both amplifiers in the SSM2211 can come to
within 400 mV of either supply rail while driving an 8 W load.
As compared to other competitors’ equivalent products, the
SSM2211 has a higher output voltage headroom. This means
that the SSM2211 can deliver an equivalent maximum output
power while running from a lower supply voltage. By running at
a lower supply voltage, the internal power dissipation of the de-
vice is reduced, as can be seen from Equation 9. This extended
output headroom, along with the Thermal Coastline package,
allows the SSM2211 to operate in higher ambient temperatures
than other competitors’ devices.
The SSM2211 is also capable of providing amplification even at
supply voltages as low as 1.7 V. The maximum power available
at the output is a function of the supply voltage. Therefore, as
the supply voltage decreases, so does the maximum power out-
put from the device. Figure 6 shows the maximum output power
versus supply voltage at various bridged-tied load resistances.
The maximum output power is defined as the point at which the
output has 1% THD.
1.6
1.4
1.2
RL = 4⍀
1.0
RL = 8⍀
0.8
0.6
RL = 16⍀
0.4
0.2
0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE – V
Figure 6. Maximum Output Power vs. VSY
To find the minimum supply voltage needed to achieve a speci-
fied maximum undistorted output power, simply use Figure 6.
For example, an application requires only 500 mW to be output
for an 8 W speaker. With the speaker connected in a bridged out-
put configuration, the minimum supply voltage required is 3.3 V.
Shutdown Feature
The SSM2211 can be put into a low power consumption shut-
down mode by connecting Pin 1 to 5 V. In shutdown mode, the
SSM2211 has an extremely low supply current of less than 10 nA.
This makes the SSM2211 ideal for battery powered applications.
Pin 1 should be connected to ground for normal operation.
Connecting Pin 1 to VDD will mute the outputs and put the
SSM2211 into shutdown mode. A pull-up or pull-down resistor is
not required. Pin 1 should always be connected to a fixed poten-
tial, either VDD or ground, and never be left floating. Leaving
Pin 1 unconnected could produce unpredictable results.
Automatic Shutdown Sensing Circuit
Figure 7 shows a circuit that can be used to automatically take
the SSM2211 in and out of shutdown mode. This circuit can be
set to turn the SSM2211 on when an input signal of a certain
amplitude is detected. The circuit will also put the SSM2211
into its low-power shutdown mode once an input signal is not
sensed within a certain amount of time. This can be useful in a
variety of portable radio applications where power conservation
is critical.
R8
VDD
C2
VIN
VDD
R5
R6
–
OP181
A2
+
R1
R3
R2
R7
VDD
R4
D1
C1
4
5
SSM2211
1
8
A1
NOTE
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 7. Automatic Shutdown Circuit
The input signal to the SSM2211 is also connected to the
non-inverting terminal of A2. R1, R2, and R3 set the threshold
voltage of when the SSM2211 will be taken out of shutdown mode.
D1 half-wave rectifies the output of A2, discharging C1 to ground
when an input signal greater than the set threshold voltage is
detected. R4 controls the charge time of C1, which sets the time
until the SSM2211 is put back into shutdown mode after the
input signal is no longer detected.
R5 and R6 are used to establish a voltage reference point equal
to half of the supply voltage. R7 and R8 set the gain of the
SSM2211. D1 should be a 1N914 or equivalent diode and A2
should be a rail-to-rail output amplifier, such as an OP181 or
equivalent. This will ensure that C1 will discharge sufficiently to
bring the SSM2211 out of shutdown mode.
REV. B
–11–
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