Datasheet

Data Sheet SSM2211
Rev. G | Page 15 of 24
THEORY OF OPERATION
The SSM2211 is a low distortion speaker amplifier that can run
from a 2.7 V to 5.5 V supply. It consists of a rail-to-rail input
and a differential output that can be driven within 400 mV of
either supply rail while supplying a sustained output current of
350 mA. The SSM2211 is unity-gain stable, requiring no
external compensation capacitors, and can be configured for
gains of up to 40 dB. Figure 41 shows the simplified schematic.
Figure 41. Simplified Schematic
Pin 4 and Pin 3 are the inverting and noninverting terminals
to A1. An offset voltage is provided at Pin 2, which must be
connected to Pin 3 for use in single-supply applications. The
output of A1 appears at Pin 5. A second operational amplifier,
A2, is configured with a fixed gain of A
V
= −1 and produces an
inverted replica of Pin 5 at Pin 8. The SSM2211 outputs at Pin 5
and Pin 8 produce a bridged configuration output to which a
speaker can be connected. This bridge configuration offers the
advantage of a more efficient power transfer from the input to
the speaker. Because both outputs are symmetric, the dc bias at
Pin 5 and Pin 8 are exactly equal, resulting in zero dc differential
voltage across the outputs. This configuration eliminates the need
for a coupling capacitor at the output.
THERMAL PERFORMANCE—LFCSP
The LFCSP offers the SSM2211 user even greater choices when
considering thermal performance criteria. For the 8-lead,
3 mm × 3 mm LFCSP, the θ
JA
is 50°C/W. This rating is a
significant performance improvement over most other
packaging options.
4
3
SHUTDOWN
V
OUT
A
V+
A2
A1
2
IN–
20kΩ
20kΩ
50kΩ
0.1µF
7
8
5
6
SSM2211
50kΩ
50kΩ
50kΩ
V
OUT
B
BIAS
CONTROL
00358-041
1