参数资料
型号: ATS651LSH
厂商: Allegro MicroSystems, Inc.
英文描述: Two-Wire Self-Calibrating Differential Speed and Direction Sensor with Vibration Immunity
中文描述: 双线自校准差分速度和方向传感器的振动免疫
文件页数: 11/12页
文件大小: 438K
代理商: ATS651LSH
11
651LSH-DS
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Two-Wire Self-Calibrating Differential Speed and Direction Sensor with Vibration Immunity
ATS651LSH
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
. (Thermal data is also available on
the Allegro MicroSystems Web site.)
The Package Thermal Resistance, R
θ
JA
, is a figure of merit sum-
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
θ
JC
, is
relatively small component of R
θ
JA
. Ambient air temperature,
T
A
, and air motion are significant external factors, damped by
overmolding.
The effect of varying power levels (Power Dissipation, 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
+
Δ
T
(3)
For example, given common conditions such as: T
A
= 25°C,
V
CC
= 5 V, I
CC
= 14 mA, and R
θ
JA
= 126 °C/W, then:
P
D
= V
CC
×
I
CC
= 12 V
×
4.0 mA = 70.0 mW
Δ
T = P
D
×
R
θ
JA
= 70.0 mW
×
126 °C/W = 8.8°C
T
J
= T
A
+
Δ
T = 25°C + 8.8°C = 23.8°C
A worst-case estimate, P
D(max)
, represents the maximum allow-
able power level (V
CC(max)
, I
CC(max)
), without exceeding T
J(max)
,
at a selected R
θ
JA
and T
A
.
Example
: Reliability for V
CC
at T
A
=
150°C, package SH, using
the PCB with least exposed copper.
Observe the worst-case ratings for the device, specifically:
R
θ
JA
=
126°C/W, T
J(max)
=
165°C, V
CC(max)
=
28
V, and
I
CC(max)
=
16.8
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 ÷ 126 °C/W = 119 mW
Finally, invert equation 1 with respect to voltage:
V
CC(est)
= P
D(max)
÷ I
CC(max)
= 119 mW ÷ 16.8 mA = 7.1 V
The result indicates that, at T
A
, the application and device can
dissipate adequate amounts of heat at voltages
V
CC(est)
.
Compare V
CC(est)
to V
CC(max)
. If V
CC(est)
V
CC(max)
, then reli-
able operation between V
CC(est)
and V
CC(max)
requires enhanced
R
θ
JA
. If V
CC(est)
V
CC(max)
, then operation between V
CC(est)
and
V
CC(max)
is reliable under these conditions.
This value applies only to the voltage drop across the
ATS651LSH chip. If a protective series diode or resistor is used,
the effective maximum supply voltage is increased.
For example, when a standard diode with a 0.7 V drop is used:
V
S(max)
= 7.1 V + 0.7 V = 7.8 V
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