SSM2250 查看數據表（PDF） - Analog Devices
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SSM2250 Datasheet PDF : 12 Pages
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0.35
0.3
VDD = 5V
0.25
RL = 4Ω
0.2
0.15
RL = 8Ω
0.1
0.05
RL = 16Ω
0
0
0.1
0.2
0.3
0.4
OUTPUT POWER (W)
Figure 16. Power Dissipation vs. Single-Ended Output Power (VDD = 5 V)
The maximum power dissipation for a single-ended output is
PDISS, MAX
=
VDD 2
2π2 RL
(5)
Because the SSM2250 is designed to drive two single-ended
loads simultaneously, the worst-case maximum power
dissipation in SE mode is twice the value of Equation 5.
A thorough mathematical explanation behind Equation 4 and
Equation 5 is provided in the SSM2211 data sheet.
Example
Given worst-case stereo headphone loads of 32 Ω, the maxi-
mum power dissipation of the SSM2250 in SE mode with a 5 V
supply is
(5 V )2
PDISS, MAX = 2π2 32 Ω = 79 mW
(6)
With an 8 Ω internal speaker attached, the maximum power
dissipation in BTL mode is (from Equation 4)
2 × (5 V )2
PDISS, MAX = π2 8 Ω = 633 mW
(7)
It can easily be seen that power dissipation from BTL mode
operation is of greater concern than SE mode.
SSM2250
Solving for Maximum Ambient Temperature
To protect the SSM2250 against thermal damage, the junction
temperature of the die should not exceed 150°C. The maximum
allowable ambient temperature of the application can be easily
found by solving for the expected maximum power dissipation
in Equation 4 and Equation 5, and using Equation 8.
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 that the SSM2250 die junction temperature stays below
150°C, the maximum ambient temperature can be solved using
Equation 8.
TAMB, MAX = + 150o C − θJA × PDISS, MAX
( ) = + 150oC − 140oC /W × 0.633 W
(8)
= + 61o C
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 17.
The y-axis corresponds to the expected maximum power
dissipation, and the x-axis is the corresponding maximum
ambient temperature. Either method returns the same answer.
1.0
14-LEAD TSSOP
0.8 θJA = 140°C/W
TJMAX = 150°C/W
FREE AIR
NO HEAT SINK
10-LEAD MSOP
0.6 θJA = 180°C/W
0.4
0.2
0
0
25
50
75
100
AMBIENT TEMPERATURE (°C)
Figure 17. 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 17 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.
Rev. A | Page 9 of 12
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