A1121 ALLEGRO [Allegro MicroSystems], A1121 Datasheet - Page 11

• Manufacturer Part Number: A1121
• Description: Chopper Stabilized Precision Hall Effect Switches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A1120, A1121
Power Derating
The device must be operated below the maximum junction
temperature of the device, T
peak conditions, reliable operation may require derating supplied
power or improving the heat dissipation properties of the appli-
cation. This section presents a procedure for correlating factors
affecting operating T
Allegro MicroSystems website.)
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
small component of R
motion are significant external factors, damped by 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

and A1125
CC
T = P
T = P
= 12 V, I
T
P
D
J
= T
= V
A
D
CC
+ T = 25°C + 3°C = 28°C
×
CC
×
R
= 1.6 mA, and R
I
JA
CC
P
T
D
J
J
= 12 V
= 19 mW
. (Thermal data is also available on the
JA
= T
= V
. Ambient air temperature, T
A
D
IN
+ ΔT
×
J(max)
×
×
R
×
1.6 mA = 19 mW
J
I
JA
, at P
IN
. Under certain combinations of
JA
165 °C/W = 3°C
Chopper Stabilized Precision Hall Effect Switches
JA
= 165 °C/W, then:
D
.
, is a figure of merit sum-
(1)
(2)
(3)
JC
A
= 25°C,
, is relatively
A
, and air
D
), can
A worst-case estimate, P
able power level (V
at a selected R
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
and V
CC
JA
JA
V
T
(max) = 4 mA.
D
CC(est)
. If V
= 228°C/W, T
(max) = T
CC
max
(max) is reliable under these conditions.
= T
= P
CC(est)
CC(est)
J
D
(max) – T
JA
(max) ÷ I
max
≥ V
and T
to V
J
(max) = 165°C, V
CC(max)
÷ R
CC
CC
(max), then operation between V
A
JA
A
CC
D(max)
(max). If V
.
CC(est)
= 165 °C – 150 °C = 15 °C
CC
, I
(max) = 66 mW ÷ 4 mA = 16.5 V
= 15°C ÷ 228 °C/W = 66 mW
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Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
CC(max)
A
at T
, the application and device can
, represents the maximum allow-
and V
A
= 150°C, package LH, using a
), without exceeding T
CC(est)
CC
CC
(max) = 24 V, and
(max) requires enhanced
J
resulting from internal
≤ V
CC
(max), then reli-
D
CC(est)
(max). First,
.
CC(est)
J(max)
11
,