LT6551 Linear Technology Corporation, LT6551 Datasheet - Page 12

• Manufacturer Part Number: LT6551
• Description: 3.3v Triple And Quad Video Amplifiers
• Manufacturer: Linear Technology Corporation

LT6550/LT6551
APPLICATIO S I FOR ATIO
Power Dissipation
The LT6550/LT6551, enhanced θ
Pin 5 (V
to the lead frame. This thermal connection increases the
efficiency of the PC board as a heat sink. The PCB material
can be very effective at transmitting heat between the pad
area attached to Pin 5 and a ground or power plane layer.
Copper board stiffeners and plated through holes can also
be used to spread the heat generated by the device. Table 1
lists the thermal resistance for several different board
sizes and copper areas. All measurements were taken on
3/32” FR-4 board with 2oz copper. This data can be used
as a rough guideline in estimating thermal resistance. The
thermal resistance for each application will be affected by
thermal interactions with other components as well as
board size and shape.
Table 1. Fused 10-Lead MSOP Package
*Device is mounted on topside.
As an example, calculate the junction temperature for the
circuit in Figure 2 assuming an 85°C ambient temperature.
The device dissipation can be found by measuring the
supply current, calculating the total dissipation and then
subtracting the dissipation in the load.
12
TOPSIDE*
(mm2)
540
100
100
30
0
COPPER AREA
EE
for the LT6550 and GND for the LT6551) fused
BACKSIDE
(mm2)
540
100
0
0
0
U
BOARD AREA
(mm2)
2500
2500
2500
2500
2500
U
JA
(JUNTION-TO-AMBIENT)
W
THERMAL RESISTANCE
MS package, has
110°C/W
120°C/W
130°C/W
135°C/W
140°C/W
U
The dissipation for the amplifiers is:
The total package power dissipation is 363mW. When a
2500 sq mm PC board with 540 sq mm of 2oz copper on
top and bottom is used, the thermal resistance is
110°C/W. The junction temperature (T
The maximum junction temperature for the LT6551 is
150°C so the heat sinking capability of the board is
adequate for the application.
P
T
J
D
1.25V
GND
= (363mW)(110°C/W) + 85°C = 125°C
= (106mA)(5V) – 4 • (2.5V)
Figure 2. Calculating Junction Temperature
LT6551
450Ω
450Ω
450Ω
450Ω
+
+
+
+
–
–
–
–
450Ω
450Ω
450Ω
450Ω
OA
OA
OA
OA
2
/150 = 363mW
5V
J
75Ω
75Ω
75Ω
75Ω
) is:
6551 F02
75Ω
75Ω
75Ω
75Ω
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