SSM2250RM 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
生产厂家
SSM2250RM Datasheet PDF : 10 Pages
| |||
SSM2250
Continuing from the previous example, the θJA of the SSM2250
14-lead TSSOP package on a 4-layer board is 140°C/W. To ensure
the SSM2250 die junction temperature stays below 150°C, the
maximum ambient temperature can be solved using Equation 8.
TAMB, MAX = +150°C − θJA × PDISS, MAX
( ) = +150°C − 140°C/W × 0.633 W (8)
= +61°C
So the maximum ambient temperature must remain below 61°C
to protect the device against thermal damage.
Another method for finding the maximum allowable ambient
temperature is to use the power derating curve in Figure 15.
The y-axis corresponds to the expected maximum power dissi-
pation, and the x-axis is the corresponding maximum ambient
temperature. Either method will return the same answer.
1.0
0.8
14-LEAD TSSOP
JA = 140؇C/W
TJ,MAX = 150؇C/W
FREE AIR
NO HEAT SINK
0.6 10-LEAD MSOP
JA = 180؇C/W
0.4
0.2
0
0
25
50
75
100
AMBIENT TEMPERATURE – ؇C
Figure 15. Maximum Power Dissipation vs. Ambient
Temperature
Maximum Output Power
The maximum amount of power that can be delivered to a
speaker is a function of the supply voltage and the resistance of
the speaker. Figure 15 shows the maximum BTL output power
possible from the SSM2250. Maximum output power is defined
as the point at which the output has greater than 1% distortion.
1.6
1.4
RL = 4⍀
1.2
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 4ϫ the power delivered to the
load. Figure 17 shows the maximum output power in SE mode vs.
supply voltage for various headphone loads.
100
75
RL = 32⍀
50
RL = 64⍀
25
RL = 128⍀
0
1.5
2.0 2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE – V
Figure 17. 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 I shows a comparison of the relative
loudness of different sounds.
Table I. 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
1.0
0.8
RL = 8⍀
0.6
0.4
RL = 16⍀
0.2
0
1.5
2.0 2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE – V
Figure 16. Maximum BTL Output Power vs. VS
It can be easily 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 shut-
down 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. Con-
necting Pin␣ 3 to VDD will shut down all amplifiers and put 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 unpredictable results.
To find the minimum supply voltage needed to achieve a speci-
fied maximum undistorted output power, simply use Figure 16.
PC 99 Compliant Computer Audio Reference Design
The schematic shown in Figure 18 is a reference design for a
complete audio system in a computer. The design is compliant
with the PC 99 standard for computer audio.
–8–
REV. 0
Share Link: 