參數(shù)資料
型號(hào): TPS2012APWP
廠商: Texas Instruments, Inc.
英文描述: POWER-DISTRIBUTION SWITCHES
中文描述: 配電開關(guān)
文件頁數(shù): 18/22頁
文件大?。?/td> 356K
代理商: TPS2012APWP
TPS2010A, TPS2011A, TPS2012A, TPS2013A
POWER-DISTRIBUTION SWITCHES
SLVS189A – DECEMBER 1998 – REVISED NOVEMBER 1999
18
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
overcurrent (continued)
Three possible overload conditions can occur. In the first condition, the output has been shorted before the
device is enabled or before V
I(IN)
has been applied (see Figure 6). The TPS201xA senses the short and
immediately switches into a constant-current output.
In the second condition, the excessive load occurs while the device is enabled. At the instant the excessive load
occurs, very high currents may flow for a short time before the current-limit circuit can react (see Figures 12–19).
After the current-limit circuit has tripped (reached the overcurrent trip threshhold) the device switches into
constant-current mode.
In the third condition, the load has been gradually increased beyond the recommended operating current. The
current is permitted to rise until the current-limit threshold is reached or until the thermal limit of the device is
exceeded (see Figures 7–10). The TPS201xA is capable of delivering current up to the current-limit threshold
without damaging the device. Once the threshold has been reached, the device switches into its
constant-current mode.
power dissipation and junction temperature
The low on-resistance on the n-channel MOSFET allows small surface-mount packages, such as SOIC, to pass
large currents. The thermal resistances of these packages are high compared to those of power packages; it
is good design practice to check power dissipation and junction temperature. The first step is to find r
DS(on)
at
the input voltage and operating temperature. As an initial estimate, use the highest operating ambient
temperature of interest and read r
DS(on)
from Figures 30–33. Next, calculate the power dissipation using:
I2
PD
rDS(on)
Finally, calculate the junction temperature:
TJ
PD
RJA
TA
Where:
T
A
= Ambient Temperature
°
C
R
θ
JA
= Thermal resistance SOIC = 172
°
C/W
Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees,
repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally
sufficient to get an acceptable answer.
thermal protection
Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for
extended periods of time. The faults force the TPS201xA into constant current mode, which causes the voltage
across the high-side switch to increase; under short-circuit conditions, the voltage across the switch is equal
to the input voltage. The increased dissipation causes the junction temperature to rise to high levels. The
protection circuit senses the junction temperature of the switch and shuts it off. Hysteresis is built into the thermal
sense circuit, and after the device has cooled approximately 20 degrees, the switch turns back on. The switch
continues to cycle in this manner until the load fault or input power is removed.
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