ATS635LSE datasheet(13/15 Pages) ALLEGRO

13 / 15 page

ATS635LSE and ATS636LSE

PROGRAMMABLE TRUE POWER-ON HALL-EFFECT GEAR-TOOTH SWITCHES

Page 13 of 15

115 Northeast Cutoff, Box 15036

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

POWER DE-RATING – SE Package

Power De -Rating

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 = 77°C/W

T J(max) = 165°C

Typical T J Calculation:

TA = 25°C, VCC = 5 V, ICC(on) = 5.5 mA

PD = VCC × ICC

PD = 5 V × 5.5 mA = 27.5 mW

∆T = PD × RθJA = 27.5 mW × 77°C/W = 2.0°

TJ = TA + ∆T = 25°C + 2.0°C = 27.0°C

Maximum Allowable Power Dissipation Calculation

TJ = TA + ∆T

TJ(max) = 165°C, if TA = 150°C then:

165 = 150 + ∆T

∆T = 15°C

DT = PD× RθJA (RθJA = 77°C/W)

\ PD(max) = 15°C / 77°C/W = 195 mW @ TA = 150°C

Maximum V CC for PD(max) =111 mW at T A=150°C

PD = VCC × ICC ICC = 10mA (max) at 150°C

VCC = PD / ICC = 195 mW / 5.5 mA = 35.4 V

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Temperature (°C)

Power Dissipation versus Ambient Temperature

(RθJA = 77 ºC/W)

2-layer PCB

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