LTC3250 datasheet(9/12 Pages) LINER

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LTC3250-1.5/LTC3250-1.2

3250fa

OPERATIO

(Refer to Simplified Block Diagram)

Figure 3. Maximum Power Dissipation vs Ambient Temperature

Thermal Management

For higher input voltages and maximum output current

there can be substantial power dissipation in the

LTC3250-1.5/LTC3250-1.2. If the junction temperature

increases above approximately 160

°C the thermal shut-

down circuitry will automatically deactivate the output. To

reduce the maximum junction temperature, a good ther-

mal connection to the PC board is recommended. Con-

necting the GND pin (Pin 2) to a ground plane, and

maintaining a solid ground plane under the device can

reduce the thermal resistance of the package and PC board

considerably.

Derating Power at Higher Temperatures

To prevent an overtemperature condition in high power

applications Figure 3 should be used to determine the

maximum combination of ambient temperature and power

dissipation. The power dissipated in the LTC3250-1.5/

LTC3250-1.2 should always fall under the line shown (i.e.

within the safe region) for a given ambient temperature.

The power dissipated in the LTC3250-1.5/LTC3250-1.2 is

given by the expression:

OUT









–

This derating curve assumes a maximum thermal resis-

tance,

θJA , of 175°C/W for the 6-pin ThinSOT-23. This

thermal resistances can be achieved from a printed circuit

board layout with a solid ground plane (2000mm2)on at

least one layer with a good thermal connection to the

ground pin of the LTC3250-1.5/LTC3250-1.2. Operation

outside of this curve will cause the junction temperature to

exceed 140

°C which may trigger the thermal shutdown

circuitry and ultimately reduce the life of the device.

AMBIENT TEMPERATURE (

°C)

–50

–25

025

3250 • F03

100

θJA = 175°C/W

TJ = 140°C

1.2

1.0

0.8

0.6

0.4

0.2

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