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LME49600_14 Datasheet(数据表) 16 Page - Texas Instruments

部件型号  LME49600
说明  High Performance, High Fidelity, High Current Audio Buffer
下载  22 Pages
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制造商  TI1 [Texas Instruments]
网页  http://www.ti.com
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LME49600 Datasheet(HTML) 16 Page - Texas Instruments

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LME49600
SNAS422D – JANUARY 2008 – REVISED MARCH 2008
www.ti.com
NOTE
The allowable thermal resistance is determined by the maximum allowable temperature
increase:
TRISE = TJ(MAX) - TA(MAX)
Thus, if ambient temperature extremes force TRISE to exceed the design maximum, the part must be de-rated by
either decreasing PD to a safe level, reducing θJA further or, if available, using a larger copper area.
Procedure
1. First determine the maximum power dissipated by the LME49600, PD(MAX). For the simple case of the buffer
driving a resistive load, and assuming equal supplies, PD(MAX) is given by:
PDMAX(AC) = (IS x VS) + (VS)
2 / (2π2R
L) (Watts)
(2)
PDMAX(DC) = (IS x VS) + (VS)
2 / R
L (Watts)
where
VS = |VEE| + VCC (V)
IS =quiescent supply current (A)
(3)
Equation (2) is for sinusoidal output voltages and Equation (3) is for DC output voltages.
2. Determine the maximum allowable die temperature rise,
TRISE(MAX) = TJ(MAX) - TA(MAX) (°C)
(4)
3. Using the calculated value of TRISE(MAX) and PD(MAX), find the required value of junction to ambient thermal
resistance combining Equation (1) and Equation (5) to derive Equation (9):
θJA = TRISE(MAX) / PD(MAX)
(5)
4. Finally, choose the minimum value of copper area from Figure 30 based on the value for
θJA.
Example
Assume the following conditions: VS = |VEE| + VCC = 30V, RL = 32Ω, IS = 15mA, sinusoidal output voltage, TJ(MAX)
= 125°C, TA(MAX) = 85°C.
Applying Equation (3):
PDMAX = (IS x VS) + (VS)
2 / 2π2R
L
= (15mA)(30V) + 900V
2 / 142Ω
= 1.86W
(6)
Applying Equation (5):
TRISE(MAX) = 125°C – 85°C
= 40°C
(7)
Applying Equation (9):
θJA = 40°C/1.86W
= 21.5°C/W
(8)
Examining the Copper Area vs.
θJA plot indicates that a thermal resistance of 50°C/W is possible with a 12in
2
plane of one layer of 1oz copper. Other solutions include using two layers of 1oz copper or the use of 2oz
copper. Higher dissipation may require forced air flow. As a safety margin, an extra 15% heat sinking capability is
recommended.
When amplifying AC signals, wave shapes and the nature of the load (reactive, non-reactive) also influence
dissipation. Peak dissipation can be several times the average with reactive loads. It is particularly important to
determine dissipation when driving large load capacitance.
The LME49600’s dissipation in DC circuit applications is easily computed using Equation (4). After the value of
dissipation is determined, the heat sink copper area calculation is the same as for AC signals.
16
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Copyright © 2008, Texas Instruments Incorporated
Product Folder Links: LME49600




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