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AAT4601 Datasheet, PDF (9/14 Pages) Advanced Analogic Technologies – 1.5A Current Limited P-Channel Switch
AAT4601
1.5A Current Limited P-Channel Switch
Applications Information
Operation in Current Limit
If an excessive load is applied to the output of an
AAT4601, the load's current will be limited by the
AAT4601's current limit circuitry. Refer to the figure
named "Overload Operation". If a short circuit were
to occur on the load, it would demand more current
than what is allowed by the internal current limiting
circuit and the voltage at the AAT4601's output will
drop. This causes the AAT4601 to dissipate more
power than in normal operation, causing the die tem-
perature to increase. When die temperature exceeds
the internal over temperature threshold, the AAT4601
will shut down. After shutting down, the AAT4601
cools to a level below the over temperature thresh-
old, at which point it will start up again. The AAT4601
will continue to cycle off and on until one of the fol-
lowing events occurs; the load current is reduced to
a level below the AAT4601's current limit setting, the
input power is removed, or until the output is turned
off by a logic high level applied to the ON pin.
Thermal Considerations
Since the AAT4601 has internal current limit and
over temperature protection, junction temperature is
rarely a concern. If an application requires a large
load current in a high temperature operating envi-
ronment, there is the possibility that the over tem-
perature protection circuit rather than the current
limit circuit will regulate the current available to the
load. In these applications, the maximum current
available without risk of activation of the over tem-
perature circuit can be calculated. The maximum
internal temperature while current limit is not active
can be calculated using Equation 1:
TJ(MAX) = IMAX2 × RDS(ON)(MAX) × RθJA + TA(MAX)
In Equation 1, IMAX is the maximum current required
by the load. RDS(ON)(MAX) is the maximum rated
RDS(ON) of the AAT4601 at high temperature. RθJA is
the thermal resistance between the AAT4601's die
and the board onto which it is mounted. TA(MAX) is
the maximum ambient temperature for the printed
circuit board assembly under the AAT4601 when the
load switch is not dissipating power. Equation 1 can
be transformed to provide IMAX; Refer to Equation 2.
IMAX=
TSD(MIN) - TA(MAX)
RDS(ON)(MAX) × RθJA
TSD(MIN) is the minimum temperature required to
activate the AAT4601's over temperature protec-
tion. With typical specification of 125°C, 115°C is a
safe minimum value to use.
For example, a portable device is specified to oper-
ate in a 50°C environment. The printed circuit
board assembly will operate at temperatures as
high as 85°C. This portable device has a sealed
case and the area of the printed board assembly is
rellatively small causing RθJA to be approximately
120°C/W. Using Equation 2,
IMAX=
115 - 85
130 × 120
= 1.4 A
If this system requires less than 1.4 A, the thermal
limit will not activate during normal operation.
Overload Operation
6
5
Input Voltage
4
3
1 9 is applied to output at t = 0
RSET is 2 k9
2
Output Voltage
1
0
-0.5
0
0.5
1
1.5
2
Time (s)
4601.2001.11.0.92
9