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參數資料
| 型號： | 2045A |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES |
| 中文描述： | 限流配電開關 |
| 文件頁數： | 20/31頁 |
| 文件大?。?/td> | 478K |
| 代理商： | 2045A |
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TPS2045A, TPS2046A, TPS2047A, TPS2048A
TPS2055A, TPS2056A, TPS2057A, TPS2058A
CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES
SLVS251A
–
SEPTEMBER 2000
–
REVISED FEBRUARY 2001
20
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
GND
IN
IN
EN
OUT
OC
OUT
OUT
TPS2045A
Rpullup
V+
Figure 25. Typical Circuit for OC Pin (Example, TPS2045A)
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. Begin by determining the r
DS(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 r
DS(on)
from Figure 18. Using this value, the
power dissipation per switch can be calculated by:
I2
PD
rDS(on)
Depending on which device is being used, multiply this number by the number of switches being used. This step
will render the total power dissipation from the N-channel MOSFETs.
Finally, calculate the junction temperature:
TJ
PD
RJA
TA
Where:
T
A
= Ambient temperature
°
C
R
θ
JA
= Thermal resistance SOIC = 172
°
C/W (for 8 pin), 111
°
C/W (for 16 pin)
P
D
= Total power dissipation based on number of switches being used.
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 a reasonable 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 TPS204xA and TPS205xA 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.
The TPS204xA and TPS205xA implement a dual thermal trip to allow fully independent operation of the power
distribution switches. In an overcurrent or short-circuit condition the junction temperature will rise. Once the die
temperature rises to approximately 140
°
C, the internal thermal sense circuitry checks which power switch is
in an overcurrent condition and turns that power switch off, thus isolating the fault without interrupting operation
of the adjacent power switch. Should the die temperature exceed the first thermal trip point of 140
°
C and reach
160
°
C, both switches turn off. The OC open-drain output is asserted (active low) when overtemperature or
overcurrent occurs.
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