ATS665LSG datasheet(13/18 Pages) ALLEGRO

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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:

∆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

Final Version, Rev 1.0; DSD; 01Aug03

115 Northeast Cutoff, Box 15036

For the sensor :

Tj(max) = 165°C

θja = 126°C/W

Typical Tj calculation:

Ta = 25 °C

Vcc = 5 V

Icc = 7.0 mA

PD = Vcc * Icc = 5 V * 8.0 mA = 40.0 mW

∆T = PD * Rθja = 40.0 mW * 126°C/W = 5.0°C

Tj = Ta +

∆T = 25 °C + 5.0°C = 30.0°C

Maximum Allowable Power Dissipation Calculation

for ATS665:

Assume:

Ta = Tamax = 165 °C

Tj(max) = 165°C

Icc = 12.0 mA

If:

4max Icc @ 150C < max Icc @ 25C, see characteristic

data

Tj = Ta +

∆T

Then, at Ta = 150 °C:

∆Tmax = Tjmax – Tamax = 165°C - 150°C = 15°C

If:

∆T = PD * Rθja

Then, at Ta = 150°C:

PDmax = ∆Tmax / Rθja = 15°C / 126°C/W = 119 mW

If:

PD = Vcc * Icc

Then the maximum Vcc at 150°C is therefore:

Vccmax = PDmax / Icc = 119 mW / 12.0 mA = 9.9 V

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.

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

used:

Vsmax = 9.9 V + 0.7 V = 10.6 V

ATS665LSG Package Power De-Rating Curve

Thermal Resistance = 126°C/Watt, Tjmax = 165°C

0.0

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100

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180

Ambient Temperature [°C]

Page 13

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

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