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PDF AAT4621 Data sheet ( Hoja de datos )
| Número de pieza | AAT4621 | |
| Descripción | PC Card Current Limit Interface and Capacitor Charger | |
| Fabricantes | AAT | |
| Logotipo |  |
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General Description
The AAT4621 SmartSwitch is a current limited P-
channel MOSFET power switch designed for high-
side load-switching applications in PC Card
GSM/GPRS/3G modem cards. Used in conjunc-
tion with a super capacitor, the AAT4621 will
ensure that the power ratings of the PCMCIA host
are not exceeded at any time. Featuring two inde-
pendent, programmable current limits and a power
loop, the AAT4621 can ensure that the super
capacitor can be charged without exceeding PCM-
CIA specifications. The current limit is set by two
external resistors allowing a ±10% current limit
accuracy over the normal operating temperature
range. The switch can be controlled from either of
the two enable inputs and in the off condition will
block currents in both directions. The AAT4621
also incorporates a System READY function which
can advise the system that the super capacitor is
fully charged and ready for use. Adjustable hys-
teresis is provided with the addition of an external
resistor. The quiescent supply current is typically a
low 40µA. In shutdown mode, the supply current
decreases to less than 1µA.
The AAT4621 is available in a thermally enhanced,
Pb-free, 12-pin TSOPJW or 14-pin TDFN33 pack-
age and is specified over the -40°C to 85°C tem-
perature range.
AAT4621
PC Card Current Limit Interface
and Capacitor Charger
Features
SmartSwitch™
• VIN Range: 3.0V to 5.5V
• Dual Independent Current Limits
— 75mA to 1200mA
— ±10% Current Accuracy
— 20°C Temperature Band
• Reverse Current Blocking Protection
• Power Loop
• Low Quiescent Current
— 40µA Typical
— 1.0µA Max with Switch Off
• 65mΩ Typical RDS(ON) at 3V
• Only 1.4V Needed for Enable Control Pin
• System READY Output with Externally
Programmable Hysteresis
• Under-Voltage Lockout
• Temperature Range: -40 to 85°C
• 12-Pin TSOPJW Package or 14-Pin TDFN33
Package
Applications
• Capacitor Charger
• CF Card Port Power Protection
• Express Card GSM/GPRS/3G Modems
• PC Card GSM/GPRS Class 10/12 Modems
• WiMAX Cards
Typical Application
V CC
ENSUPERCAP
EN OPERATION
VCC
EN IL
Under-
Voltage
Lockout
Reverse
Blocking
Over-Temp
Protection
Power
Loop
EN IU
1.2V
Reference
GND
Current
Limit
Control
RHYS
OUT
RDY
100kΩ
To Load
To μC
ISETL
ISETU
RSETU
RSETL
SuperCap
4621.2007.07.1.0
1
1 page  
Typical Characteristics
Output Current vs. Output Voltage
(RSETU = 249KΩ; T = 25°C)
0.30
0.25 VIN = 5V
0.20
0.15
0.10 VIN = 3.3V
0.05
0.00
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Output Voltage (V)
5
Reverse Off-Switch Current vs. Temperature
(ENUB = ENLB = VCC; VIN = 0V)
100
10
VOUT = 5V
1
0.1 VOUT = 3.3V
0.01
-40
-20
0 20 40 60 80
Temperature (°C)
100 120
Off-Supply Current vs. Temperature
(ENUB = ENLB = VCC; VOUT = Open)
10
VIN = 5V
1
0.1
VIN = 3.3V
0.01
-40
-20
0 20 40 60 80
Temperature (°C)
100 120
AAT4621
PC Card Current Limit Interface
and Capacitor Charger
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0
RSET vs. ILIM
(25°C)
VIN = 3.3V
VIN = 5V
200 400 600 800 1000 1200 1400 1600
RSET (kΩ)
Off-Switch Current vs. Temperature
(ENUB = ENLB = VCC; VOUT = 0V)
100
10
VIN = 5V
1
0.1
0.01
-40
-20
VIN = 3.3V
0 20 40 60
Temperature (°C)
80
100 120
4621.2007.07.1.0
5
5 Page 
ILOAD vs. RSETU and RSETL
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.10
0.30
0.50
0.70
0.90
1.10
1.30
1.50
RSETU and RSETL (MΩ)
Figure 1: Calculated Current Limit RSET
Characteristic.
System Ready Hysteresis (RHYS) and
System Ready (RDY)
In internal comparator senses the output voltage
and delivers a ready signal to the external micro
controller when the output voltage reaches 98% of
the final value (VCC). The comparator hysteresis is
programmed by a resistor from the RHYS pin to
ground. The RHYS voltage determines the hys-
teresis voltage and is equal to the RHYS source
current (1µA) times the RHYS resistance.
VHYST = RHYS · 1μA
= 200kΩ · 1μA
= 0.2V
The system ready pin (RDY) is an open drain out-
put that switches low when the output voltage
reaches 98% of the input voltage. It requires an
external pull up resistor tied to the input voltage
with a typical value of 100kΩ.
Power Loop
The AAT4621 power loop limits the load current in
the event that the device power dissipation becomes
excessive. The AAT4621 power loop regulates the
die temperature to 110°C, decreasing the load cur-
rent in increments of 1/32 of the current limit set point
when the die temperature reaches 110°C. When the
die temperature exceeds 110°C it decreases the
load current by 1/32 of the current limit set point. If
4621.2007.07.1.0
AAT4621
PC Card Current Limit Interface
and Capacitor Charger
die temperature is less than 110°C, it increases the
load current in increments of 1/32 of the current limit
set point until the set current limit point is reached or
the die temperature exceeds 110°C.
The delay time between die temperature measure-
ments varies depending on the load current limit
set point. The delay ranges from 0.5ms for a 75mA
current limit set point to 4ms for a 1.2A current limit
set point.
For the condition where there is no current limit set
point (shorting RSETU or RSETL to ground) the soft
start increments the current limit is 1/32 steps of
1.2A until the current reaches 1.2A, at which point
the power MOSFET turns on fully. At this point, the
current is limited by the RDS(ON) of the power MOS-
FET and other series resistance. The Power Loop
and Over-Temperature Loop then takes control to
limit the current until the output voltage has fully
charged.
Over-Temperature Protection
If the die temperature rate of rise is fast enough to
exceed the power loop regulated temperature,
over-temperature shutdown disables the device.
The over-temperature threshold is 145°C. After
over-temperature shutdown, soft start is initiated
once the die temperature drops to 130°C.
Short Circuit Protection
The series pass power MOSFET turns off complete-
ly after the output has charged to within 18mV of the
input voltage. This protects the device in the event
where a short circuit is applied to the output. After
applying a short circuit or heavy load to the output,
which causes the output to sink below the 18mV
threshold plus some hysteresis, the current will
immediately attempt to slew from zero to the final
programmed value. The device will continue to out-
put the current limit as long as the output is VIN -
18mV or until the die temperature reaches 110ºC. If
temperature foldback occurs, then the power loop
will become active.
Under-Voltage Shutdown
Under-voltage lockout enables the device at 2.7V
typical with 100mV of hysteresis. The maximum
UVLO level is 3.0V.
11
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