ATS645 Allegro MicroSystems, Inc., ATS645 Datasheet - Page 12

• Manufacturer Part Number: ATS645
• Description: Ats645lsh True Zero Speed Miniature Gear-tooth Sensors
• Manufacturer: Allegro MicroSystems, Inc.

ATS645LSH
The device must be operated below the maximum junction
temperature of the device, T
peak conditions, reliable operation may require derating sup-
plied power or improving the heat dissipation properties of the
application. This section presents a procedure for correlating
factors affecting operating T
the Allegro MicroSystems Web site.)
The Package Thermal Resistance, R
marizing the ability of the application and the device to dissipate
heat from the junction (die), through all paths to the ambient air.
Its primary component is the Effective Thermal Conductivity,
K, of the printed circuit board, including adjacent devices and
traces. Radiation from the die through the device case, R
relatively small component of R
T
overmolding.
The effect of varying power levels (Power Dissipation, P
be estimated. The following formulas represent the fundamental
relationships used to estimate T
For example, given common conditions such as: T
V
A worst-case estimate, P
able power level (V
at a selected R
A
CC
, and air motion are signifi cant external factors, damped by
ΔT = P
= 12 V, I
P
T
D
J
= T
= V
A
D
CC
+ ΔT = 25°C + 7°C = 32°C
×
CC
θJA
×
R
= 4 mA, and R
I
θJA
and T
CC
ΔT = P
P
T
CC(max)
D
J
= 12 V
= 48 mW
= T
= V
A
D(max)
.
A
D
IN
, I
+ ΔT
×
J(max)
J
×
CC(max)
×
. (Thermal data is also available on
R
, represents the maximum allow-
×
4 mA = 48 mW
I
θJA
J
θJA
θJA
, at P
IN
. Under certain combinations of
140 °C/W = 7°C
= 140 °C/W, then:
. Ambient air temperature,
), without exceeding T
(2)
θJA
D
.
, is a fi gure of merit sum-
True Zero Speed Miniature Differential Peak-
(1)
(3)
A
= 25°C,
Power Derating
θJC
D
), can
J(max)
, is
,
Example: Reliability for V
(I1 trim), using minimum-K PCB
Observe the worst-case ratings for the device, specifi cally:
R
I
Calculate the maximum allowable power level, P
invert equation 3:
This provides the allowable increase to T
power dissipation. Then, invert equation 2:
Finally, invert equation 1 with respect to voltage:
The result indicates that, at T
dissipate adequate amounts of heat at voltages ≤V
Compare V
able operation between V
R
V
CC(max)
θJA
θJA
CC(max)
P
V
ΔT
D(max)
CC(est)
. If V
= 126°C/W, T
max
Detecting Gear Tooth Sensor
= 16 mA.
is reliable under these conditions.
= T
= ΔT
= P
CC(est)
CC(est)
J(max)
D(max)
max
≥ V
to V
J(max)
÷ R
– T
÷ I
CC(max)
θJA
CC(max)
A
CC(max)
= 165°C, V
= 165 °C – 150 °C = 15 °C
CC(est)
= 15°C ÷ 126 °C/W = 119 mW
115 Northeast Cutoff, Box 15036
CC
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
, then operation between V
A
. If V
at T
= 119 mW ÷ 16 mA = 7 V
, the application and device can
and V
A
CC(est)
= 150°C, package SH
CC(max)
CC(max)
J
≤ V
= 24 V, and
resulting from internal
CC(max)
requires enhanced
D(max)
CC(est)
, then reli-
CC(est)
. First,
.
and
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