LT1010CDD datasheet(15/20 Pages) LINER

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LT1010

1010fc

APPLICATIO S I FOR ATIO

Typical thermal calculations for the miniDIP package are

detailed in the following paragraphs.

For 4.8mA supply current (typical at 50

°C, 30V supply

voltage—see supply current graphs) to the LT1010 at

±15V, PD = power dissipated in the part is equal to:

(30V)(0.0048A) = 0.144W

The rise in junction is then:

(0.144W)(130

°C/W—This is θJA for the N package)

= 18.7

°C.

This means that the junction temperature in 50

°C ambient

air without driving any current into a load is:

18.7

°C + 50°C = 68.7°C

Using the LT1010 to drive 8V DC into a 200

Ω load using

±15V power supplies dissipates PD in the LT1010 where:

OUT

= ()()

= ()( )

Ω

+ –

–

200

0 280

This causes the LT1010 junction temperature to rise

another (0.280W)(0.130

°C/W) = 36.4°C.

This heats the junction to 68.7

°C + 36.4°C = 105.1°C.

Caution: This exceeds the maximum operating tempera-

ture of the device.

An example of 1MHz operation further shows the limita-

tions of the N (or miniDIP) package. For

±15V operation:

PD at IL = 0 at 1MHz* = (10mA)(30V) = 0.30W

This power dissipation causes the junction to heat from

°C (ambient in this example) to 50°C + (0.3W)

(130

°C/W) = 89°C. Driving 2VRMS of 1MHz signal into a

200

Ω load causes an additional

D =

Ω

⎛

⎝⎜

⎞

⎠⎟ ()

200

15 2

0 130

•–

to be dissipated, resulting in another (0.130W)

(0.130

°C/W) = 16.9°C rise in junction temperature to

°C + 16.9°C = 105.9°C.

Caution: This exceeds the maximum operating tempera-

ture of the device.

Thermal Resistance of DFN Package

For surface mount devices, heat sinking is accomplished

by using the heat spreading capabilities of the PC board

and its copper traces. Copper board stiffeners and plated

through-holes can also be used to spread the heat gener-

ated by power devices.

The following table 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 one ounce

copper.

Table 1. DFN Measured Thermal Resistance

COPPER AREA

THERMAL RESISTANCE

TOPSIDE

BACKSIDE

BOARD AREA

(JUNCTION-TO-AMBIENT)

2500 sq mm

°C/W

1000 sq mm

2500 sq mm

°C/W

225 sq mm

2500 sq mm

°C/W

100 sq mm

2500 sq mm

°C/W

For the DFN package, the thermal resistance junction-to-

case (

θJC),measuredattheexposedpadonthebackofthe

die, is 16

°C/W.

Continuous operation at the maximum supply voltage and

maximum load current is not practical due to thermal

limitations. Transient operation at the maximum supply is

possible. The approximate thermal time constant for a

2500sq mm 3/32" FR-4 board with maximum topside and

backside area for one ounce copper is 3 seconds. This time

constant will increase as more thermal mass is added (i.e.

vias, larger board, and other components).

For an application with transient high power peaks, aver-

age power dissipation can be used for junction tempera-

ture calculations as long as the pulse period is significantly

less than the thermal time constant of the device and

board.

*See Supply Current vs Frequency graph.

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