SSM2250 데이터 시트보기 (PDF) - Analog Devices
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SSM2250 Datasheet PDF : 12 Pages
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SSM2250
1.6
1.4
1.2
RL = 4Ω
1.0
0.8
0.6
RL =8Ω
0.4
RL = 16Ω
0.2
0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
Figure 18. Maximum BTL Output Power vs. VS
Use Figure 18 to find the minimum supply voltage needed to
achieve a specified maximum undistorted output power.
The output power in SE mode is exactly one-fourth the
equivalent output power in BTL mode. This is because twice the
voltage swing across the two BTL outputs results in 4 × the
power delivered to the load. Figure 19 shows the maximum
output power in SE mode vs. supply voltage for various
headphone loads.
100
75
RL = 32Ω
50
RL = 64Ω
25
RL = 128Ω
0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
Figure 19. Maximum SE Output Power vs. VS
Example
An application requires only 500 mW to be output in BTL
mode into an 8 Ω speaker. By inspection, the minimum supply
voltage required is 3.3 V.
Speaker Efficiency and Loudness
The effective loudness of 1 W of power delivered into an 8 Ω
speaker is a function of the efficiency of the speaker. The
efficiency of a speaker is typically rated at the sound pressure
level (SPL) at 1 meter in front of the speaker with 1 W of power
applied to the speaker. Most speakers are between 85 dB and
95 dB SPL at one meter at 1 W of power. Table 5 shows a com-
parison of the relative loudness of different sounds.
Table 5. Typical Sound Pressure Levels
Source of Sound
Threshold of Pain
Heavy Street Traffic
Cabin of Jet Aircraft
Average Conversation
Average Home at Night
Quiet Recording Studio
Threshold of Hearing
dB SPL
120
95
80
65
50
30
0
It can easily be seen that 1 W of power into a speaker can
produce quite a bit of acoustic energy.
Shutdown Feature
The SSM2250 can be put into a low power consumption
shutdown mode by connecting Pin 3 to VDD. In shutdown
mode, the SSM2250 has low supply current of 60 μA.
Pin 3 should be connected to ground for normal operation.
Connecting Pin 3 to VDD shuts down all amplifiers and puts
all outputs into a high impedance state, effectively muting the
SSM2250. A pull-up or pull-down resistor is not required.
Pin 3 should never be left floating, as this could produce unpre-
dictable results.
PC99-Compliant Computer Audio Reference Design
The schematic shown in Figure 20 is a reference design for a
complete audio system in a computer. The design is compliant
with the PC99 standard for computer audio.
The AD1881A is an AC’97, version 2.1, audio codec, available
from Analog Devices. The stereo output from the AD1881A is
coupled into the SSM2250, which is used to drive a mono
internal speaker and stereo headphones. The internal speaker
switching is controlled by the SSM2250 through the normaliz-
ing pin on the headphone jack. The AD1881A controls the
shutdown pin on the SSM2250, and is activated through the
power management software drivers installed on the computer.
For more information, refer to the AD1881A data sheet.
Rev. A | Page 10 of 12
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