lme49610ts National Semiconductor Corporation, lme49610ts Datasheet - Page 13

• Manufacturer Part Number: lme49610ts
• Description: High Performance, High Fidelity, High Current Audio Buffer
• Manufacturer: National Semiconductor Corporation

area attains a nominal value of 20°C/W junction to ambient
thermal resistance (θ
A copper plane may be placed directly beneath the tab. Ad-
ditionally, a matching plane can be placed on the opposite
side. If a plane is placed on the side opposite of the
LME49610, connect it to the plane to which the buffer’s metal
tab is soldered with a matrix of thermal vias per JEDEC Stan-
dard JESD51-5.
Determining Copper Area
Find the required copper heat sink area using the following
guidelines:
1. Determine the maximum power dissipation of the
LME49610, P
2. Specify a maximum operating ambient temperature, T
(MAX).
T
from junction to ambient, θ
such that T
perature of 150°C.
3. Specify a maximum allowable junction temperature, T
(MAX)
is drawing maximum current (quiescent and load). It is pru-
dent to design for a maximum continuous junction tempera-
ture of 100°C to 130°C. Ensure, however, that the junction
temperature never exceeds the 150°C absolute maximum
rating for the part.
4. Calculate the value of junction to ambient thermal resis-
tance, θ
5. θ
in Figure 6. Choose a copper area that will guarantee the
specified T
of junction to ambient thermal resistance, θ
where:
T
FIGURE 6. Thermal Resistance (typ) for 5 lead TO-263
A
J(MAX)
by an amount that is dependent on the thermal resistance
JA
, This is the LME49610’s die temperature when the buffer
Note that the die temperature, T
as a function of copper area in square inches is shown
θ
= the maximum recommended junction temperature
JA
JA
.
= (T
J
J(MAX)
Package Mounted on 1oz. copper
does not exceed the absolute maximum die tem-
D
.
J(MAX)
for the calculated θ
- T
JA
) under zero air flow.
A(MAX)
JA
. Therefore, T
) / P
D(MAX)
JA
. The maximum value
J
, will be higher than
(°C/W)
A
must be specified
JA
, is defined as:
30042562
(1)
A
J
13
T
LME49610’s environment
P
Note: The allowable thermal resistance is determined by the
maximum allowable temperature increase:
Thus, if ambient temperature extremes force T
the design maximum, the part must be de-rated by either de-
creasing P
able, using a larger copper area.
Procedure
1. First determine the maximum power dissipated by the
LME49610, P
a resistive load, and assuming equal supplies, P
en by:
where:
V
I
Equation (2) is for sinusoidal output voltages and (3) is for DC
output voltages
2. Determine the maximum allowable die temperature rise,
3. Using the calculated value of T
the required value of junction to ambient thermal resistance
combining equation 1 and equation 4 to derive equation 5:
4. Finally, choose the minimum value of copper area from
Figure 6 based on the value for θ
Example
Assume the following conditions: V
= 32Ω, I
C, T
Applying Equation (2):
Applying Equation (4):
S
A(MAX)
D(MAX)
S
= quiescent supply current (A)
P
= |V
A(MAX)
DMAX(AC)
P
EE
DMAX(DC)
= the maximum recommended power dissipation
S
= the maximum ambient temperature in the
| + V
θ
T
= 15mA, sinusoidal output voltage, T
= 85°C.
D
JA
RISE(MAX)
to a safe level, reducing θ
= (I
D(MAX)
= T
P
CC
= (15mA)(30V) + 900V
DMAX
= (I
S
(V)
RISE(MAX)
T
T
x V
RISE(MAX)
. For the simple case of the buffer driving
RISE
S
= T
= (I
x V
S
) + (V
J(MAX)
S
= T
S
x V
) + (V
= 1.87W
/ P
= 40°C
J(MAX)
= 125°C – 85°C
S
D(MAX)
S
)
- T
) + (V
2
S
/ (2
)
A(MAX)
JA
2
- T
RISE(MAX)
/ R
π
.
S
S
A(MAX)
= |V
)
2
2
2
(°C/W)
R
L
JA
/ 2
/ 632Ω
L
)
, further, or, if avail-
EE
(Watts)
π
°C
| + V
2
and P
(Watts)
R
L
RISE
J(MAX)
CC
D(MAX)
www.national.com
D(MAX)
to exceed
= 30V, R
= 125°
is giv-
, find
(2)
(3)
(4)
(5)
L