MIC2007YML datasheet(28/30 Pages) MICREL

28 / 30 page

Micrel, Inc.

MIC20xx Family

August 2011

M9999-080211-D

In Figure 12, die temperature is plotted against IOUT

assuming a constant case temperature of 85°C. The

plots also assume a worst case RON of 140mΩ at a die

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 140°C die temperature,

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

reason we recommend using MLF

® packaged switches

for any design intending to supply continuous currents

of 1A or more.

Power Dissipation

Power dissipation depends on several factors such as

the load, PCB layout, ambient temperature, and supply

voltage. Calculation of power dissipation can be

accomplished by the following equation:

)

(

OUT

)

(

To relate this to junction temperature, the following

equation can be used:

100

120

140

160

0.2

OUTPUT CURRENT (A)

Die Temperature vs.

Output Current (T CASE=85°C)

SOT-23

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

MLF

)

(

−

where:

TJ = junction temperature

TA = ambient temperature

Rθ(J-A) is the thermal resistance of the package

In normal operation the switch’s RON is low enough that

no significant I

2R heating occurs. Device 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 switch’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.

Figure 12. Die Temperature vs. IOUT

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