参数资料
型号: TPS2553DRV-1
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO6
封装: PLASTIC, SON-6
文件页数: 9/32页
文件大小: 2005K
代理商: TPS2553DRV-1
POWER DISSIPATION AND JUNCTION TEMPERATURE
www.ti.com...................................................................................................................................... SLVS841C – NOVEMBER 2008 – REVISED SEPTEMBER 2009
While both the constant-current devices (TPS2552/53) and latch-off devices (TPS2552-1/53-1) operate identically
during the initial onset of an overcurrent event, they behave differently if the overcurrent event lasts longer than
the internal delay "deglitch" circuit (7.5-ms typ). The constant-current devices (TPS2552/53) assert the FAULT
flag after the deglitch period and continue to regulate the current to the current-limit threshold indefinitely. In
practical circuits, the power dissipation in the package will increase the die temperature above the
overtemperature shutdown threshold (135°C min), and the device will turn off until the die temperature decreases
by the hysteresis of the thermal shutdown circuit (10°C typ). The device will turn on and continue to thermal cycle
until the overload condition is removed. The constant-current devices resume normal operation once the
overload condition is removed. The latch-off devices (TPS2552-1/53-1) assert the FAULT flag after the deglitch
period and immediately turn off the device. The device remains off regardless of whether the overload condition
is removed from the output. The latch-off devices remain off and do not resume normal operation until the
surrounding system either toggles the enable or cycles power to the device.
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) × IOUT
2
Where:
PD = Total power dissipation (W)
rDS(on) = Power switch on-resistance ()
IOUT = Maximum current-limit threshold (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)
θ
JA = 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
θ
JA, 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 2008–2009, Texas Instruments Incorporated
17
Product Folder Link(s): TPS2552 TPS2553 TPS2552-1 TPS2553-1
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