LT1806/LT1807
18
18067fc
or 8-lead MSOP package. All packages have the V
–
sup-
ply pin fused to the lead frame to enhance the thermal
conductance when connecting to a ground plane or a
large metal trace. Metal trace and plated through-holes
can be used to spread the heat generated by the device
to the backside of the PC board. For example, on a 3/32"
FR-4 board with 2oz copper, a total of 660 square mil-
limeters connects to Pin 4 of LT1807 in an SO-8 package
(330 square millimeters on each side of the PC board) will
bring the thermal resistance, θ
JA
, to about 85°C/W. Without
extra metal trace beside the power line connecting to the
V
–
pin to provide a heat sink, the thermal resistance will be
around 105°C/W. More information on thermal resistance
for all packages with various metal areas connecting to
the V
–
pin is provided in Tables 1, 2 and 3.
Table 1. LT1806 6-Lead SOT-23 Package
COPPER AREA
BOARD AREA
(mm
2
)
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE (mm
2
)
270 2500 135°C/W
100 2500 145°C/W
20 2500 160°C/W
0 2500 200°C/W
Device is mounted on topside.
Table 2. LT1806/LT1807 SO-8 Package
COPPER AREA
BOARD AREA
(mm
2
)
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE
(mm
2
)
BACKSIDE
(mm
2
)
1100 1100 2500 65°C/W
330 330 2500 85°C/W
35 35 2500 95°C/W
35 0 2500 100°C/W
0 0 2500 105°C/W
Device is mounted on topside.
APPLICATIONS INFORMATION
Table 3. LT1807 8-Lead MSOP Package
COPPER AREA
BOARD AREA
(mm
2
)
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE
(mm
2
)
BACKSIDE
(mm
2
)
540 540 2500 110°C/W
100 100 2500 120°C/W
100 0 2500 130°C/W
30 0 2500 135°C/W
0 0 2500 140°C/W
Device is mounted on topside.
Junction temperature T
J
is calculated from the ambient
temperature T
A
and power dissipation P
D
as follows:
T
J
= T
A
+ (P
D
• θ
JA
)
The power dissipation in the IC is the function of the supply
voltage, output voltage and the load resistance. For a given
supply voltage, the worst-case power dissipation P
D(MAX)
occurs at the maximum quiescent supply current and at
the output voltage which is half of either supply voltage
(or the maximum swing if it is less than 1/2 the supply
voltage). P
D(MAX)
is given by:
P
D(MAX)
= (V
S
• I
S(MAX)
) + (V
S
/2)2/R
L
Example: An LT1807 in SO-8 mounted on a 2500mm
2
area of PC board without any extra heat spreading plane
connected to its V
–
pin has a thermal resistance of
105°C/W, θ
JA
. Operating on ±5V supplies with both ampli-
fi ers simultaneously driving 50Ω loads, the worst-case
power dissipation is given by:
P
D(MAX)
= 2 • (10 • 14mA) + 2 • (2.5)
2
/50
= 0.28 + 0.25 = 0.53W
