SSM2250RMZ-REEL Analog Devices Inc, SSM2250RMZ-REEL Datasheet - Page 7

• Manufacturer Part Number: SSM2250RMZ-REEL
• Description: IC AMP AUDIO PWR 1.5W AB 10MSOP
• Manufacturer: Analog Devices Inc
• Series: SoundMAX®r
• Type: Class ABr

Specifications of SSM2250RMZ-REEL

• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.5W x 1 @ 8 Ohm; 90mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 6 V
• Features: Depop, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Operational Class: Class-AB
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.2@1.5W%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Unity Gain Bandwidth Product (typ): 4MHz
• Rail/rail I/o Type: Rail to Rail Output
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 6V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 10
• Package Type: MSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PRODUCT OVERVIEW
The SSM2250 is a low distortion power amplifier that can
drive a set of stereo headphones or a single 8 Ω loudspeaker. It
contains three rail-to-rail output op amps, click-and-pop reduc-
tion biasing, and all necessary switching circuitry. In SE (single-
ended) mode, the device automatically mutes the internal 8 Ω
speaker. In BTL (bridge-tied load) mode, the internal speaker
is activated.
The SSM2250 can operate from a 2.7 V to a 5.5 V single supply.
The rail-to-rail outputs can be driven to within 400 mV of
either supply rail while supplying a sustained output current
of 350 mA into 8 Ω. The device is unity-gain stable and requires
no external compensation capacitors. The SSM2250 can be
configured for gains of up to 40 dB.
TYPICAL APPLICATION
In SE mode, the device operates similarly to a high current
output, dual op amp. A1 and A3 are independent amplifiers
with a gain of −R2/R1. The outputs of A1 and A3 are used to
drive the external headphones plugged into the headphone jack.
Amplifier A2 is shut down to a high output impedance state.
This prevents current from flowing through the 8 Ω internal
speaker, thereby muting it.
Although the gains of A1 and A3 can be set independently,
it is recommended that the feedback and feedforward resistor
around both amplifiers be equal. This prevents one channel
from becoming louder than the other.
In BTL mode, the current into the right in pin is directed to the
input of A1. This effectively sums the left in and right in audio
signals. The A2 amplifier is activated and configured with a
fixed gain of A
figuration that drives the internal speaker. Because the BTL
output voltages swing opposite to each other, the gain to the
speaker in BTL mode is twice the gain of SE mode. The voltage
across the internal speaker can be written
The bridged output configuration offers the advantage of a
more efficient power transfer from the input to the speaker.
Because both outputs are symmetric, the dc voltage bias across
the 8 Ω internal speaker is 0. This eliminates the need for a
coupling capacitor at the output. In BTL mode, the A3 amplifier
is shut down to conserve power.
V
SPEAKER
=
V
(
= −1. This produces a balanced output con-
V
LEFT
+
V
RIGHT
)
×
2
×
R
R
2
1
Rev. A | Page 7 of 12
(1)
In BTL mode, the SSM2250 can achieve 1 W continuous output
into 8 Ω at ambient temperatures up to 40°C. The power
derating curve shown in Figure 17 should be observed for
proper operation at higher ambient temperatures. For a
standard 14-lead TSSOP package, typical junction-to-ambient
temperature thermal resistance (θ
board and 140°C/W on a 4-layer board.
Internal Speaker/External Headphones Automatic
Switching
Pin 4 on the SSM2250 controls the switching between the BTL
mode and the SE mode. Logic low to Pin 4 activates BTL mode,
while logic high activates SE mode. The configuration shown in
Figure 14 provides the appropriate logic voltages to Pin 4,
muting the internal speaker when headphones are plugged into
the jack.
A stereo headphone jack with a normalizing pin is required for
the application. With no plug inserted, a mechanical spring
connects the normalizing pin to the output pin in the jack.
Once a plug is inserted, this connection is broken.
In Figure 14, Pin 4 of the SSM2250 is connected to the nor-
malizing pin for the right channel output. This pin, located in
the headphone jack, hits the ring on the headphone plug. A
100 kΩ pull-up resistor to 5 V is also connected at this point.
With a headphone plug inserted, the normalizing pin discon-
nects from the output pin, and Pin 4 is pulled up to 5 V,
activating SE mode on the SSM2250. This mutes the internal
speaker while driving the stereo headphones.
Once the headphone plug is removed, the normalizing pin
connects to the output pin. This drives the voltage at Pin 4
to 50 mV, as this point is pulled low by the 1 kΩ resistor now
connected to the node. The SSM2250 goes into BTL mode,
deactivating the right SE amplifier to prevent the occurrence
of any false mode switching.
It is important to connect Pin 4 and the 100 kΩ pull-up resistor
to the normalizing pin for the right output in the headphone
jack. Connecting them to the left output normalizing pin results
in improper operation from the device. The normalizing pin to
the left output in the headphone jack should be left open.
Coupling Capacitors
Output coupling capacitors are not required to drive the
internal speaker from the BTL outputs. However, coupling
capacitors are required between the amplifier’s SE outputs and
the headphone jack to drive external headphones. This prevents
dc current from flowing through the headphone speakers,
whose resistances are typically about 80 Ω.
JA
) is 180°C/W on a 2-layer
SSM2250