参数资料
型号: TPS2561DRC
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO10
封装: GREEN, SON-10
文件页数: 7/24页
文件大小: 942K
代理商: TPS2561DRC
www.ti.com
SLVS930 – DECEMBER 2009
POWER DISSIPATION AND JUNCTION TEMPERATURE
The low on-resistance of the N-channel MOSFET allows small surface-mount packages to pass large currents. It
is good design practice to estimate power dissipation and junction temperature. The below analysis gives an
approximation for calculating junction temperature based on the power dissipation in the package. However, it is
important to note that thermal analysis is strongly dependent on additional system level factors. Such factors
include air flow, board layout, copper thickness and surface area, and proximity to other devices dissipating
power. Good thermal design practice must include all system level factors in addition to individual component
analysis.
Begin by determining the rDS(on) of the N-channel MOSFET relative to the input voltage and operating
temperature. As an initial estimate, use the highest operating ambient temperature of interest and read rDS(on)
from the typical characteristics graph. Using this value, the power dissipation can be calculated by:
PD = (RDS(on) × IOUT1
2) +(R
DS(on) × IOUT2
2)
Where:
PD = Total power dissipation (W)
rDS(on) = Power switch on-resistance of one channel ()
IOUTx = Maximum current-limit threshold set by RILIM(A)
This step calculates the total power dissipation of the N-channel MOSFET.
Finally, calculate the junction temperature:
TJ = PD × θJA + TA
Where:
TA = Ambient temperature (°C)
θJA = Thermal resistance (°C/W)
PD = Total power dissipation (W)
Compare the calculated junction temperature with the initial estimate. If they are not within a few degrees, repeat
the calculation using the "refined" rDS(on) from the previous calculation as the new estimate. Two or three
iterations are generally sufficient to achieve the desired result. The final junction temperature is highly dependent
on thermal resistance
θJA, and thermal resistance is highly dependent on the individual package and board
layout. The Dissipating Rating Table provides example thermal resistances for specific packages and board
layouts.
Copyright 2009, Texas Instruments Incorporated
15
Product Folder Link(s): TPS2560 TPS2561
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