ATS672LSB-HT datasheet(11/12 Pages) ALLEGRO

11 / 12 page

ATS672LSB

SELF-CALIBRATING TPOS GEAR-TOOTH SENSOR WITH 9-BIT SIGNAL CAPTURE

Preliminary – Subject to Change

Rev. 1.2 May 1, 2002

Page 11 of 12

115 Northeast Cutoff, Box 15036

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

Power Derating Curve: ATS672LSB Package

Power Derating

Due to internal power consumption, the temperature of the

IC (junction temperature, Tj) is higher than the ambient

environment temperature, Ta. To ensure that the device

does not operate above the maximum rated junction

temperature use the following calculations:

∆T=PD * RθJA

Where PD=Vcc * Icc

∴ ∆T=Vcc * Icc * RθJA

Where

∆T denotes the temperature rise resulting from the

IC’s power dissipation:

TJ = TA + ∆T

RθJA =150°C/W TJ(max) = 170°C

Typical TJ Calculation:

TA =25°C, Vcc=5 V, Icc(On)=6.5 mA

PD=Vcc * Icc

PD= 5 V * 6.5 mA = 32.5 mW

∆T=PD* RθJA = 32.5 mW * 150°C/W = 4.9°

TJ = TA + ∆T = 25°C + 4.9°C = 29.9°C

Maximum Allowable Power Dissipation Calculation

TJ = TA + ∆T

TJ (max) = 170°C, if TA=160°C then:

170 = 160 +

∆T

∆T = 10°C

∆T = PD* RθJA (RθJA = 150°C/W)

∴ PD(max) = 10°C / 150°C/W = 66.6 mW @ TA = 160°C

Maximum Vcc for PD(max) =111 mW at TA=160°C

PD=Vcc * Icc Icc = 10 mA (max) at 160°C

Vcc = PD / Icc = 66.6 mW / 10 mA = 6.66 V

Maximum Power Dissipation vs. Ambient Temperature

SB Package: Thermal Resistance: 150°C/Watt

100

200

300

400

500

600

700

800

900

1000

100 110 120 130 140 150 160 170

Ambient Temperature [°C]

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