参数资料
型号: A3425LL-T
元件分类: 模拟信号调理
英文描述: SPECIALTY ANALOG CIRCUIT, PDSO8
封装: LEAD FREE, PLASTIC, MS-012AA, SOIC-8
文件页数: 2/21页
文件大小: 484K
代理商: A3425LL-T
Ultra-Sensitive Dual-Channel Quadrature
Hall-Effect Bipolar Switch
A3425
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Typical Thermal Performance
The device must be operated below the maximum junction
temperature of the device, TJ(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 TJ. (Thermal data is also available on
the Allegro MicroSystems Web site.)
The Package Thermal Resistance, RθJA, is a gure 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, RθJC, is
relatively small component of RθJA. Ambient air temperature,
TA, and air motion are signicant external factors, damped by
overmolding.
The effect of varying power levels (Power Dissipation, PD), can
be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.
PD = VIN
× IIN
(1)
ΔT = PD
× RθJA (2)
TJ = TA + ΔT
(3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 4 mA, and RθJA = 140 °C/W, then:
PD = VCC
× ICC = 12 V × 4 mA = 48 mW
ΔT = PD
× RθJA = 48 mW × 140 °C/W = 7°C
TJ = TA + ΔT = 25°C + 7°C = 32°C
A worst-case estimate, PD(max), represents the maximum allow-
able power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RθJA and TA.
Example: Reliability for VCC at TA=150°C, package L, using
minimum-K PCB
Observe the worst-case ratings for the device, specically:
RθJA=140°C/W, TJ(max) =165°C, VCC(max)=18V, and
ICC(max) = 6mA.
Calculate the maximum allowable power level, PD(max). First,
invert equation 3:
ΔTmax = TJ(max) – TA = 165°C–150°C = 15°C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = ΔTmax÷RθJA =15°C÷140 °C/W=107mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max)= 107mW÷6mA=18 V
The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤VCC(est).
Compare VCC(est) to VCC(max). If VCC(est) ≤ VCC(max), then reli-
able operation between VCC(est) and VCC(max) requires enhanced
RθJA. If VCC(est) ≥ VCC(max), then operation between VCC(est) and
VCC(max) is reliable under these conditions.
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