Current Limited Load Switch
the value of R
SET
may also be calculated using the
I
LIM
R
SET
product found in the chart "R
SET
Coefficient vs. I
LIM
". The maximum current is
derived by multiplying the typical current for the
chosen R
SET
in the chart by 1.25. A few standard
resistor values are listed in Table 1.
Device Will Device Always
Current Not Current Current Limits
R
SET
Limit
Limit Below
Below
Ω
(kΩ) Typ (mA)
(mA)
(mA)
40.2
30.9
24.9
22.1
19.6
17.8
16.2
14.7
13.0
10.5
8.87
7.50
6.81
6.04
5.49
4.99
4.64
200
250
300
350
400
450
500
550
600
700
800
900
1000
1100
1200
1300
1400
150
188
225
263
300
338
375
413
450
525
600
675
750
825
900
975
1050
250
313
375
438
500
563
625
688
750
875
1000
1125
1250
1375
1500
1625
1750
AAT4610
imately 0.700A as a typical I
LIM
value for 10.5kΩ.
Multiplying 0.700A by 0.75 and 1.25 shows that the
AAT4610 will limit the load current to greater than
0.525A but less than 0.875A.
Operation in Current Limit
When a heavy load is applied to the output of the
AAT4610, the load current is limited to the value of
I
LIM
determined by R
SET
(see Figure 2). Since the
load is demanding more current than I
LIM
, the volt-
age at the output drops. This causes the AAT4610 to
dissipate a larger than normal quantity of power, and
results in increased die temperature. When the die
temperature exceeds an over-temperature limit, the
AAT4610 will shut down until is has cooled suffi-
ciently, at which point it will start up again. The
AAT4610 will continue to cycle on and off until the
load is removed, power is removed, or until a logic
high level is applied to ON (Pin 4).
Enable Input
In many systems, power planes are controlled by
integrated circuits which run at lower voltages than
the power plane itself. The enable input ON (Pin 4)
of the AAT4610 has low and high threshold volt-
ages that accommodate this condition. The thresh-
old voltages are compatible with 5V TTL and 2.5V
to 5V CMOS.
Table 1: Current Limit R
SET
Values.
Example: A USB port requires 0.5A. 0.5A multiplied
by 1.33 is 0.665A. From the chart "R
SET
vs. I
LIM
," R
SET
should be less than 11kΩ. 10.5 kΩ is a standard value
that is a little less than 11kΩ. The chart gives approx-
Reverse Voltage
The AAT4610 is designed to control current flowing
from IN to OUT. If a voltage is applied to OUT which
is greater than the voltage on IN, large currents may
flow. This could damage the AAT4610.
1
0.75
Output Voltage (V)
0.5
0.25
0
5
4
3
2
1
0
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
Output Current (A)
Output Current
1Ω load is turned on at time = 0
Output Voltage
Figure 2: Overload Operation.
4610.2006.09.1.3
Not recommended for new designs; pin-for-pin upgrade: AAT4610A.
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
