AAT4620_12 Datasheet, PDF (10/14 Pages) Skyworks Solutions Inc. – PCMCIA Current Limit Interface and Capacitor Charger

DATA SHEET
AAT4620
PCMCIA Current Limit Interface and Capacitor Charger
threshold is specified by I_LIM(MIN). If the load condition
maintains the device in current limit and the chip tem-
perature reaches a critical point, then an internal power
loop will reduce the current to a safe level. Connecting
ISETU to ground disables the current limit protection
allowing a low impedance path to the host V_CC.
The load switch is turned off by applying a logic high
level to both of the EN pins. When both EN IL and EN IU
are selected ISETU will be selected. The EN function has
logic level thresholds that allow the AAT4620 to be TTL
compatible and may also be controlled by 2.5V to 5.0V
CMOS circuits. The voltage level applied to the EN pins
should not exceed the input supply level present on the
VCC pin. The AAT4620 typically consumes 40μA when
operating, when off, the device draws less then 1μA. In
the off state, current is prevented from flowing between
the input and output.
Under-voltage lockout circuitry ensures that the V_CC sup-
ply is high enough for correct operation of the IC. Also
included is a System Ready function which will be acti-
vated when the capacitor voltage is charged and the load
is permitted to take current. For automatic functionality,
this pin can be directly connected to the EN IU pin. An
external resistor is provided to add hysteresis to this
function.
Application Information
ISETU and ISETL Current Limit Set
The AAT4620 current limit is set at two different levels.
Resistors from ISETL and ISETU set the lower and upper
current limit levels respectively.
The ISETL and ISETU nodes operate within a window of
0.75V to 1.5V for resistor values ranging from 93.75 to
1.5M. Resistor values outside this range are not recom-
mended. The ISETL and ISETU source current varies with
the resistor value used according to Table 1. To determine
the resulting current limit multiply the R_SETU or R_SETL node
voltage times the gain in Table 1. Note that the voltage at
the node varies from 0.75V to 1.5V and the current limit
gain varies depending on the resistor value used.
V_ISET = R_SET · I_ISET = 0.75V to 1.5V
If the set pin is open circuit or allowed to exceed 2V, all
power devices are disabled and the input is disconnected
from the output. Shorting the set pin to GND enables all
power devices and shorts the V_CC to the output pin with
no current limit.
To activate the upper current level (R_SETU) pull EN IU low.
To activate the lower current level (R_SETL) pull EN IL low.
If both EN IU and EN IL are pulled low the EN IU current
limit level (R_SETU) will be selected.
R_SET Range
1.5Meg - 750k
750k - 375k
375k - 187.5k
187.5 - 93.75k
I_ISET (μA)
1
2
4
8
I_LIM/V_ISET (A/V)
0.8
0.4
0.2
0.1
Current Limit Range (A)
1.2-0.6
0.6-0.3
0.3-0.15
0.15-0.075
Table 1: R_SET Table.
Current Limit
R_SET*1μA*0.8
R_SET*2μA*0.4
R_SET*4μA*0.2
R_SET*8μA*0.1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201943A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012