ATS665LSG

TRUE ZERO-SPEED GEAR TOOTH SENSOR

POWER DE-RATING

Due to internal power consumption, the junction

temperature of the IC, 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:

Tj = Ta +

ΔT

Then, at Ta = 150 °C:

= Tj

– Ta

= 165°C - 150°C = 15°C

max

max

If:

ΔT = P * Rθja

* R

θja

ΔT = P

D

D

Where: P = Vcc * Icc

Then, at Ta = 150°C:

D

=

ΔT

/ R

θja = 15°C / 126°C/W = 119 mW

max

∴ ΔT=Vcc * Icc * Rθja

If:

Where

ΔT denotes the temperature rise resulting from

the IC’s power dissipation.

P = Vcc * Icc

D

Then the maximum Vcc at 150°C is therefore:

Tj = Ta +

ΔT

Vccmax = P

/ Icc = 119 mW / 12.0 mA = 9.9 V

Dmax

For the sensor :

This value applies only to the voltage drop across the

665 chip. If a protective series diode or resistor is used,

the effective maximum supply voltage is increased.

Tj(max) = 165°C

R

θja = 126°C/W

Typical Tj calculation:

For example, when a standard diode with a 0.7 V drop is

used:

Ta = 25 °C

Vsmax = 9.9 V + 0.7 V = 10.6 V

Vcc = 5 V

Icc = 7.0 mA

Final Version, Rev 2.0; MN; 19Dec05

Page 13

115 Northeast Cutoff, Box 15036

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

Copyright © 1993, 1995, 2005 Allegro MicroSystems, Inc.

ATS665LSG Package Power De-Rating Curve

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180

Ambient Temperature [°C]

c

ΔT = P * Rθja = 40.0 mW * 126°C/W = 5.0°C

D

Tj = Ta +

ΔT = 25 °C + 5.0°C = 30.0°C

Maximum Allowable Power Dissipation Calculation

for ATS665:

Assume:

Tj(max) = 165°C

4

Icc = 12.0 mA

If:

data