LT6550CMS datasheet(12/16 Pages) LINER

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LT6550/LT6551

65501f

Power Dissipation

The LT6550/LT6551, enhanced

θJA MS package, has

Pin 5 (VEE for the LT6550 and GND for the LT6551) fused

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

COPPER AREA

TOPSIDE*

BACKSIDE

BOARD AREA

THERMAL RESISTANCE

(mm2)

(JUNTION-TO-AMBIENT)

540

2500

110

°C/W

100

2500

120

°C/W

100

2500

130

°C/W

2500

135

°C/W

2500

140

°C/W

*Device is mounted on topside.

As an example, calculate the junction temperature for the

circuit in Figure 2 assuming an 85

°Cambienttemperature.

The device dissipation can be found by measuring the

supply current, calculating the total dissipation and then

subtracting the dissipation in the load.

The dissipation for the amplifiers is:

PD = (106mA)(5V) – 4 • (2.5V)2/150 = 363mW

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 (TJ) is:

TJ = (363mW)(110°C/W) + 85°C = 125°C

The maximum junction temperature for the LT6551 is

150

°C so the heat sinking capability of the board is

adequate for the application.

Figure 2. Calculating Junction Temperature

–

1.25V

450

Ω

450

Ω

–

450

Ω

450

Ω

–

450

Ω

450

Ω

–

GND

450

Ω

450

Ω

LT6551

6551 F02

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