AAT4621_12 Datasheet, PDF (11/17 Pages) Skyworks Solutions Inc. – PC Card Current Limit Interface and Capacitor Charger

DATA SHEET
AAT4621
PC Card Current Limit Interface and Capacitor Charger
Functional Block Diagram
VCC
Reverse
Blocking
OUT
EN IL
EN IU
Under-
Voltage
Lockout
Over-Temp
Protection
Power
Loop
RDY
1.2V
Reference
Current Limit
Control
ISETL
ISETU
GND
Functional Description
The AAT4621 SmartSwitch family is an integrated
P-channel MOSFET load switch with an upper and lower
adjustable current limits which can be enabled indepen-
dently, over temperature protection, a power loop and a
super capacitor charger. The current limit control is com-
bined with an over temperature thermal limit and power
loop circuit to provide a comprehensive system to pro-
tect the load switch and its supply from load conditions
which exceed the supply specifications. The AAT4621
has been designed specifically to provide the interface
between a PCMCIA host and PC card where a super
capacitor has been used to “average out” high pulse cur-
rents which would otherwise exceed the PCMCIA/
Express Card power specifications. e.g. GSM/ GPRS
modem cards, where pulse currents during transmit sig-
nals can exceed the 1A maximum specification (1.3A in
the case of Express Card).
The current limit and over temperature circuits act inde-
pendently. The device current limit is activated when the
output load current exceeds an internal threshold level.
There are two internal current limits which are enabled
independently. The current limit threshold in each case
is determined by external resistors connected between
the two SET pins and ground. The minimum current limit
RHYS
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 AAT4621 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 AAT4621 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
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