參數(shù)資料
型號： A1205LUA-T
廠商： Allegro MicroSystems, Inc.
英文描述： Continuous-Time Bipolar Switch
中文描述： 連續(xù)時間雙極開關(guān)
文件頁數(shù)： 10/12頁
文件大?。?/td> 705K
代理商： A1205LUA-T
Continuous-Time Bipolar Switch
A1205
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Power Derating
Power Derating
The device must be operated below the maximum junction
temperature of the device, T
J(max)
. Under certain combinations of
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
J
.(Thermaldataisalsoavailableon
theAllegroMicroSystemsWebsite.)
ThePackageThermalResistance,R
θ
JA
, is a figure of merit sum-
marizing the ability of the application and the device to dissipate
heatfromthejunction(die),throughallpathstotheambientair.
ItsprimarycomponentistheEffectiveThermalConductivity,
K, of the printed circuit board, including adjacent devices and
traces.Radiationfromthediethroughthedevicecase,R
θ
JC
, is
relativelysmallcomponentofR
θ
JA
. Ambient air temperature,
T
A
, and air motion are significant external factors, damped by
overmolding.
Theeffectofvaryingpowerlevels(PowerDissipation,P
D
),can
be estimated. The following formulas represent the fundamental
relationships used to estimate T
J
, at P
D
.
P
D
= V
IN
×
I
IN
(1)
Δ
T = P
D
×
R
θ
JA
(2)
T
J
= T
A
+ΔT
(3)
For example, given common conditions such as: T
A
= 25°C,
V
CC
= 12 V
,I
CC
= 4 mA, and
R
θ
JA
=140°C/W,t
hen:
P
D
= V
CC
×
I
CC
= 12 V
×
4mA=48mW
Δ
T = P
D
×
R
θ
JA
=48mW
×
140°C/W=7°C
T
J
= T
A
+
Δ
T = 25°C + 7°C = 32°C
A worst-case estimate, P
D(max)
, represents the maximum allow-
ablepowerlevel(V
CC(max)
,I
CC(max)
),withoutexceedingT
J(max)
,
ataselectedR
θ
JA
and T
A
.
Example
:ReliabilityforV
CC
at T
A
=
150°C, package UA, using
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
R
θ
JA
=
165°C/W,T
J(max)
=
165°C, V
CC(max)
=
24 V, and
I
CC(max)
=
7.5
mA.
Calculate the maximum allowable power level, P
D(max)
. First,
invert equation 3:
Δ
T
max
= T
J(max)
– T
A
= 165
°C
–
150
°C = 15
°C
This provides the allowable increase to T
J
resulting from internal
power dissipation. Then, invert equation 2:
P
D(max)
=
Δ
T
max
÷R
θ
JA
=15°C÷165°C/W=91mW
Finally, invert equation 1 with respect to voltage:
V
CC(est)
= P
D(max)
÷I
CC(max)
=
91mW÷7.5
mA = 12.1 V
The result indicates that, at T
A
, the application and device can
dissipateadequateamountsofheatatvoltages≤V
CC(est)
.
Compare V
CC(est)
to V
CC(max)
.IfV
CC(est)
≤V
CC(max)
, then reli-
able operation between V
CC(est)
and V
CC(max)
requires enhanced
R
θ
JA
.IfV
CC(est)
≥V
CC(max)
, then operation between V
CC(est)
and
V
CC(max)
is reliable under these conditions.
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