SSM2211S Analog Devices Inc, SSM2211S Datasheet - Page 18

• Manufacturer Part Number: SSM2211S
• Description: IC AMP AUDIO PWR 1W MONO 8SOIC
• Manufacturer: Analog Devices Inc
• Type: Class ABr

Specifications of SSM2211S

• Rohs Status: RoHS non-compliant
• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 1.5W x 1 @ 4 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Differential Inputs, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)

SSM2211
The input signal to the SSM2211 is also connected to the non-
inverting terminal of A2. R1, R2, and R3 set the threshold
voltage at which the SSM2211 is to be taken out of shutdown
mode. The diode, 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. A 1N914 or equivalent diode is required for D1, and
A2 must be a rail-to-rail output amplifier, such as AD8500 or
equivalent. This ensures that C1 discharges sufficiently to bring
the SSM2211 out of shutdown mode.
To find the appropriate component values, the gain of A2 must
be determined by
where:
V
V
A
properly.
Next, choose R1 and set R2 to
Find R3 as
C1 can be arbitrarily set but should be small enough to prevent
A2 from becoming capacitively overloaded. R4 and C1 control
the shutdown rate. To prevent intermittent shutdown with low
frequency input signals, the minimum time constant must be
where f
SY
THS
V
must be set to a minimum of 2 for the circuit to work
is the single supply voltage.
is the threshold voltage.
A
R2
R3
R4
V,
LOW
=
=
MIN
×
R1
R2
R1
is the lowest input frequency expected.
C1
=
⎛
⎜
⎜
⎝
×
+
≥
1
V
R2
V
R2
−
THS
f
SY
LOW
10
A
2
(
V
A
V
⎞
⎟
⎟
⎠
−
1
)
(12)
(13)
(14)
(15)
Rev. E | Page 18 of 24
SHUTDOWN-CIRCUIT DESIGN EXAMPLE
In this example, a portable radio application requires the SSM2211
to be turned on when an input signal greater than 50 mV is
detected. The device needs to return to shutdown mode within
500 ms after the input signal is no longer detected. The lowest
frequency of interest is 200 Hz, and a 5 V supply is used.
The minimum gain of the shutdown circuit, from Equation 12, is
A
R2 = 98 kΩ and R3 = 4.9 MΩ. C1 is set to 0.01 μF, and based on
Equation 15, R4 is set to 10 MΩ. To minimize power supply
current, R5 and R6 are set to 10 MΩ. The previous procedure
provides an adequate starting point for the shutdown circuit.
Some component values may need to be adjusted empirically to
optimize performance.
START-UP POPPING NOISE
During power-up or release from shutdown mode, the midrail
bypass capacitor, C
starts up. By adjusting the charging time constant of C
up pop noise can be pushed into the subaudible range, greatly
reducing start-up popping noise. On power-up, the midrail
bypass capacitor is charged through an effective resistance of
25 kΩ. To minimize start-up popping, the charging time constant
for C
the input coupling capacitor, C
For an application where R1 = 10 kΩ and C
be at least 0.1 μF to minimize start-up popping noise.
SSM2211 Amplifier Design Example
Maximum output power: 1 W
Input impedance: 20 kΩ
Load impedance: 8 Ω
Input level: 1 V rms
Bandwidth: 20 Hz − 20 kHz ± 0.25 dB
The configuration shown in Figure 42 is used. The first thing to
determine is the minimum supply rail necessary to obtain the
specified maximum output power. From Figure 46, for 1 W of
output power into an 8 Ω load, the supply voltage must be at
least 4.6 V. A supply rail of 5 V can be easily obtained from a
V
= 100. R1 is set to 100 kΩ. Using Equation 13 and Equation 14,
C
B
B
needs to be greater than the charging time constant for
× 25 kΩ > C
B
, determines the rate at which the SSM2211
C
× R1
C
.
C
= 0.22 μF, C
B
, the start-
B
must
(16)