LT1207CS datasheet(12/16 Pages) LINER

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LT1207

resistance between the layer is small. Copper board stiff-

eners and plated through holes can also be used to spread

the heat generated by the device.

Table 1 lists thermal resistance for several different board

sizes and copper areas. All measurements were taken in

still air on 3/32" FR-4 board with 2oz copper. This data can

be used as a rough guideline in estimating thermal resis-

tance. 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 16-Lead SO Package

TOTAL

THERMAL RESISTANCE

TOPSIDE

BACKSIDE

COPPER AREA (JUNCTION-TO-AMBIENT)

2500 sq. mm

5000 sq. mm

°C/W

1000 sq. mm

2500 sq. mm

3500 sq. mm

°C/W

600 sq. mm

2500 sq. mm

3100 sq. mm

°C/W

180 sq. mm

2500 sq. mm

2680 sq. mm

°C/W

180 sq. mm

1000 sq. mm

1180 sq. mm

°C/W

180 sq. mm

600 sq. mm

780 sq. mm

°C/W

180 sq. mm

300 sq. mm

480 sq. mm

°C/W

180 sq. mm

100 sq. mm

280 sq. mm

°C/W

180 sq. mm

0 sq. mm

180 sq. mm

°C/W

where:

TJ = Junction Temperature

TA = Ambient Temperature

PD = Device Dissipation

θJA = Thermal Resistance (Junction-to-Ambient)

As an example, calculate the junction temperature for the

circuit in Figure 8 assuming a 70

°C ambient temperature.

The device dissipation can be found by measuring the

supply currents, calculating the total dissipation and then

subtracting the dissipation in the load and feedback

network.

APPLICATI

I FOR ATIO

The dissipation for each amplifier is:

PD = (37.5mA)(30V) – (12V)

2/(1k||1k) = 0.837W

The total dissipation is PD = 1.674W. When a 2500 sq mm

PC board with 2oz copper on top and bottom is used, the

thermal resistance is 40

°C/W.ThejunctiontemperatureTJis:

TJ = (1.674W)(40°C/W) + 70°C = 137°C

The maximum junction temperature for the LT1207 is

150

°C, so the heat sinking capability of the board is

adequate for the application.

If the copper area on the PC board is reduced to 280mm2

the thermal resistance increases to 60

°C/W and the junc-

tion temperature becomes:

TJ = (1.674W)(60°C/W) + 70°C = 170°C

Which is above the maximum junction temperature indi-

cating that the heat sinking capability of the board is

inadequate and should be increased.

COPPER AREA (2oz)

COPPER AREA (mm2)

LT1207 • F07

2000

5000

1000

3000

4000

Figure 7. Thermal Resistance vs Total Copper Area

(Top + Bottom)

Calculating Junction Temperature

The junction temperature can be calculated from the

equation:

TJ = (PD)(θJA) + TA

–

15V

–15V

0.01

µF

330

Ω

200pF

–12V

12V

f = 2MHz

37.5mA

LT1206 • F07

1/2 LT1207

SHDN

Figure 8. Thermal Calculation Example

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