Micrel

MIC2007/MIC2017

October 2005

16

M9999-102805

equation can be used:

A

A)

-

(J

D

J

T

R

P

T

+

×

=

θ

enough that no significant I

heating is most often caused by a short circuit — or very

heavy load — when a significant portion of the input

supply voltage appears across the MIC2007/2017’s

power MOSFET. Under these conditions, the heat

generated will exceed the package and PCB’s ability to

cool the device and thermal limiting will be invoked.

assuming a constant case temperature of 85°C. The

temperature of 135°C. Under these conditions, it is clear

that an SOT-23 packaged device will be on the verge of

thermal shutdown (typically 145°C die temperature)

when operating at a load current of 1.25A. For this

reason, it is recommend that MLF package be used for

any

MIC2007/2017

designs

intending

to

supply

continuous currents of 1A or more.

Die Temperature vs. Iout for Tcase = 85°C

0

20

40

60

80

100

120

140

160

0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Iout - Amps

SOT-23

MLF

Figure 10. Die Temperature vs. Package

Figure 10 assumes no backside contact is made to the

thermal pad provided on the MLF package. For optimal

performance at higher current levels, or in higher

temperature environments, thermal contact with the

PCB and the exposed power paddle on the back side of

the MLF package should be made. This significantly

reduces the package’s thermal resistance thereby

extending the MIC2007/2017’s operating range. It

should be noted that this backside paddle is electrically

active and is connected to the MIC2007/2017’s GND

pin.

2 Vias

0.3 mm diam.

to Ground Plane

0.8 mm

1.4 mm

Figure 11. Pad for Thermal Mounting to PCB