AAT4608 Datasheet, PDF (7/10 Pages) Advanced Analogic Technologies – Current Limited Load Switch in SOT-23 Package

AAT4608
Current Limited Load Switch in SOT-23 Package
Applications Information
Setting Current Limit
In most applications, the variation in I_LIM must be
taken into account when determining R_SET. The I_LIM
variation is due to processing variations from part
to part, as well as variations in the voltages at IN
(pin 5) and OUT (pin 3), plus the operating temper-
ature. See charts "Current Limit vs. Temperature",
and "Output Current vs. V_OUT". Together these
three factors add up to a ±25% tolerance (see I_LIM
specification in Electrical Characteristics section).
In the figure below, a cold device with a statistical-
ly higher current limit, and a hot device with a sta-
tistically lower current limit, both with R_SET equal to
10.5kΩ are shown. While the chart, "R_SET vs. I_LIM"
indicates an I_LIM of 0.7A with an R_SET of 10.5kΩ ,
this figure shows that the actual current limit will be
at least 0.525A, and no greater than 0.880A.
Current Limit Using 10.5 kΩ
1.2
1
0.88 A
Device with high current limit at -40°C
0.8
0.6
0.4
0.525 A
0.2
Device with low current limit at 85°C
0
0
1
2
3
4
5
V_OUT ( V )
To determine R_SET, start with the maximum current
drawn by the load, and multiply it by 1.33. (typi-
cal_I_LIM = minimum_I_LIM / 0.75) This is the typical
current limit value. Next, refer to "R_SET vs. I_LIM" and
find the R_SET that corresponds to the typical current
limit value. Choose the largest resistor available
that is less than or equal to it. For greater precision,
the value of R_SET may also be calculated using the
I_LIM R_SET product found in the chart "R_SET coeffi-
cient 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 the table "Current Limit R_SET Values".
Current Limit R_SET Values
R_SET
(kΩ)
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
Current
Limit typ
(mA)
200
250
300
350
400
450
500
550
600
700
800
900
1000
1100
1200
1300
1400
Device will
not current
limit below:
(mA)
150
188
225
263
300
338
375
413
450
525
600
675
750
825
900
975
1050
Device always
current limits
below:
(mA)
250
313
375
438
500
563
625
688
750
875
1000
1125
1250
1375
1500
1625
1750
Example: A USB port requires 0.5A. 0.5A multiplied
by 1.33 is 0.665A. From the chart named "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 but
very close. The chart reads approximately 0.700A
as a typical I_LIM value for 10.5kΩ. Multiplying
0.700A by 0.75 and 1.25 shows that the AAT4608
will limit the load current to greater than 0.525A but
less than 0.875A.
4608.2001.10.0.9
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