A3251LLT Allegro Microsystems Inc, A3251LLT Datasheet - Page 14

• Manufacturer Part Number: A3251LLT
• Description: IC SW HALL EFFECT UNI SOT-89
• Manufacturer: Allegro Microsystems Inc
• Type: Unipolar Switchr

Specifications of A3251LLT

• Sensing Range: 50G
• Voltage - Supply: 4.2 V ~ 24 V
• Current - Supply: 10mA
• Current - Output (max): 20mA
• Output Type: Digital, Open Collector
• Features: Regulated Voltage
• Operating Temperature: -40°C ~ 150°C
• Package / Case: SOT-89-3
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A3250
A3251
Power Derating
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

V

A worst-case estimate, P
able power level (V
at a selected R
For example, given common conditions such as: T
A
CC
, and air motion are significant external factors, damped by
T = P
T = P
= 12 V, I
T
P
D
J
= T
= V
A
D
CC
+ T = 25°C + 8°C = 33°C
×
CC
JA
×
and
R
= 4 mA, and R
I
JA
and T
CC
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
, represents the maximum allow-
R
×
JA
4 mA = 48 mW
J
I
JA
JA
, at P
IN
. Under certain combinations of
165 °C/W = 8°C
. Ambient air temperature,
= 165 °C/W, then:
), without exceeding T
(2)
JA
D
.
, is a figure of merit sum-
(1)
(3)
Field-Programmable, Chopper-Stabilized,
A
= 25°C,
JC
D
), can
J(max)
, is
,
Example: Reliability for V
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
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:
P
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)
JA
JA
CC(max)
V
T
D(max)
CC(est)
Unipolar Hall-Effect Switches
. If V
= 165°C/W, T
max
= 10 mA.
is reliable under these conditions.
= T
= T
= P
CC(est)
CC(est)
J(max)
D(max)
max
≥ V
to V
J(max)
÷ R
– T
÷ I
CC(max)
JA
CC(max)
A
CC(max)
= 165°C, V
= 165 °C – 150 °C = 15 °C
= 15°C ÷ 165 °C/W = 91 mW
CC(est)
CC
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
, then operation between V
A
. If V
at T
= 91 mW ÷ 10 mA = 9 V
, the application and device can
and V
A
CC(est)
= 150°C, package UA, using
CC(max)
CC(max)
≤ V
J
= 24 V, and
resulting from internal
CC(max)
requires enhanced
D(max)
CC(est)
, then reli-
CC(est)
. First,
.
and
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