ATS672LSB datasheet(13/15 Pages) ALLEGRO

13 / 15 page

30Dec03, Rev. 1.42

Worcester, Massachusetts 01615-0036 (508) 853-5000

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

Self-Calibrating Gear Tooth Sensor with 9-Bit Signal Capture

ATS672LSB

Example: VCC Adjustment, Package SE

Observe the absolute maximum ratings for the package,

speciﬁcally:

RθJA = 150 °C/W

TJ(max) = 170°C

Also observe the characteristic operating maximums:

VCC(max) = 26.5 V

ICC(max) = 11 mA

For a given TA (e.g., 150°C), ﬁrst calculate the Maximum Allow-

able Power Dissipation, PD(max). Invert equation 1:

∆Tmax = TJ(max) – TA = 170°C – 150°C = 20°C

This provides the allowable increase to TJ resulting from internal

power dissipation. Then, invert equation 2:

PD(max) = ∆Tmax÷RθJA =20°C÷150 °C/W=133mW

This provides the corresponding allowable increase in power

level. Finally, invert equation 3 to determine the corresponding

supply voltage VCC:

VCC = PD(max) ÷ ICC(max)=133mW÷11mA=12 V

The result indicates that the device and package can dissipate

adequate amounts of heat at voltages up to 12 V, at TA = 150ºC.

Because VCC(max) is more than the calculated VCC, however, the

device requires additional heat sinking for operation between the

calculated VCC and VCC(max), under these conditions. If the cal-

culated VCC were greater than or equal to VCC(max), then opera-

tion up to VCC(max) would not require additional heat sinking.

vs. Ambient Temperature

Maximum Pow er Dissipation

Package SB: RθJA = 150ºC/W, TJ(max) = 170ºC

100

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100

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180

TA (ºC)

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