AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
General Description
The AAT4621 SmartSwitch family 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 conjunction with a super capaci-
tor, the AAT4621 will ensure that the power ratings of
the PCMCIA host are not exceeded at any time. Featuring
two independent, programmable current limits and a
power loop, the AAT4621 can ensure that the super
capacitor can be charged without exceeding PCMCIA
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 hysteresis is
provided with the addition of an external resistor. The
quiescent supply current is typically a low 40μA. In shut-
down mode, the supply current decreases to less than
1μA. The AAT4621 has a current limit range from 75mA
to 1200mA; the AAT4621-1 has a current limit range
from 150mA to 2400mA.
The AAT4621 is available in a thermally enhanced,
Pb-free 14-pin TDFN33 package and is specified over the
-40°C to 85°C temperature range.
Features
• Operating Voltage Range: 3.0V to 5.5V
• Dual Independent Current Limits
▪ AAT4621: 75mA to 1200mA
▪ AAT4621-1: 150mA to 2400mA
▪ ±10% Current Accuracy
• Reverse Current Blocking Protection
• Power Loop
• Low Quiescent Current
▪ 40μA Typical
▪ 1.0μA Max with Switch Off
• 65m Typical RDS(ON) at 3V
• System READY Output with Externally Programmable
Hysteresis
• Only 1.4V Needed for Enable Control Pin
• Under-Voltage Lockout
• Over-Temperature Protection
• Temperature Range: -40 to 85°C
• 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
GND
EN IL
EN IU
ISETU
ISETL
OUT
RDY
RSETU RSETL
SuperCap
To Load
VCC
VCC
100k
To μC
RHYS
Under-
Voltage
Lockout
1.2V
Reference
Current
Limit
Control
Reverse
Blocking
Over-Temp
Protection Power
Loop
ENIL
ENIU
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Pin Descriptions
Pin # Symbol Function
1RDY System ready pin. Open drain, active low, initiated when the capacitor is 98% charged.
2 RHYS System READY hysteresis. Connect a resistor to ground to set the System Ready comparator hysteresis.
3 ISETU
Upper current limit set input. A resistor from ISETL to ground sets the maximum upper current limit for
the switch. The AAT4621 has a current limit range from 75mA to 1200mA; the AAT4621-1 has a current
limit range from 150mA to 2400mA. Connect to ground to disable current limit.
4 ISETL
Lower current-limit set input. A resistor from ISETU to ground sets the maximum lower current limit for
the switch. The AAT4621 has a current limit range from 75mA to 1200mA; the AAT4621-1 has a current
limit range from 150mA to 2400mA. Connect to ground to disable current limit.
5, 6, 7 OUT P-channel MOSFET drain connection. Connect to super capacitor from OUT to GND.
8, 9, 10, 11 VCC Input pins to the P-channel MOSFET source. Connect 1μF capacitor from VCC to GND.
12 GND Device ground connection.
13 EN IL Enable input. Active low enable with internal pull up. Also switches in the lower current limit initiating
the super capacitor to start charging.
14 EN IU
Enable input. Active low enable with internal pull up. Also switches in the higher current limit to allow the
System to start functioning. Can be directly connected to System Ready for automatic enabling. When
both EN IL B and EN IU B are enabled, ISETU will be selected.
EP EP
The exposed thermal pad (EP) must be connected to the board ground plane and Pin 12. The ground
plane should include a large exposed copper pad under the package for thermal dissipation (see pack-
age outline).
Pin Configuration
TDFN33-14
(Top View)
RDY
ISETU
ISETL
1
OUT
OUT
OUT
EP
ENIU
GND
VCC
VCC
VCC
VCC
RHYS 2
3
4
5
6
7
14
ENIL
13
12
11
10
9
8
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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Absolute Maximum Ratings1
Symbol Description Value Units
VCC VCC to GND -0.3 to 6.0 V
VEN ENIL, ENIU to GND -0.3 to VCC + 0.3 V
VSET
, VOUT ISETL, ISETU, OUT to GND -0.3 to VCC + 0.3 V
IMAX Maximum Continuous Switch Current 2.5 A
TJMaximum Junction Operating Temperature Range -40 to +150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec.) 300 °C
T
STG Storage Temperature Range -65 to 150 °C
Thermal Characteristics
Symbol Description Value Units
JA Maximum Thermal Resistance250 °C/W
PD Maximum Power Dissipation22W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Electrical Characteristics1
VCC = 3.0V to 5.5V, TA = -40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C.
Symbol Description Conditions Min Typ Max Units
AAT4621
VCC Operation Voltage 3.0 5.5 V
IQQuiescent Current EN IL or EN IU = VCC, IOUT = 0, RHYS = 200k40 75 μA
IQU0 Quiescent Current U0
EN IL = VCC, EN IU = GND, IOUT = 0, ISET =
GND, RHYS = 200k40 75 μA
IQ(OFF) Off Supply Current EN IL = EN IU = VCC 0.4 1.0 μA
ISD(OFF) Off Switch Current EN IL = EN IU = VCC, VSUPERCAP = 0 0.4 10 μA
VUVLO Under-Voltage Lockout Rising edge, 1% hysteresis 2.7 3.0 V
RDS(ON) On-Resistance VCC = 4.75V, RSETL = RSETU = 0k 50 100 m
VCC = 3.0V, RSETL = RSETU = 0k 65 120
ILIMACC Lower Current Limit Accuracy RSETL = 249KΩ; ΔTA ≤ 25°C 180 200 220 mA
RSETL = 249KΩ170 200 230
ILIMACC Upper Current Limit Accuracy RSETU = 1.24MΩ; ΔTA ≤ 25°C 900 1000 1100 mA
RSETU = 1.24MΩ850 1000 1150
ILIM(MIN) Minimum Current Limit 75 mA
VEN(L) EN Input Low Voltage VCC = 3.0V to 5.5V20.4 V
VEN(H) EN Input High Voltage VCC = 3.0V to 5.5V21.4 V
IEN(SINK) EN Input Leakage VEN = 5.5V 1.0 μA
TDEL(OFF) Turn-Off Delay Time VCC = 5V 0.4 1.0 μs
VRDY System READY Trip Threshold VOUT rising, TA = 25°C 98 % of VOUT
VRDYHYS System READY Hysteresis RHYS = 200k200 mV
VRDY(L) System READY Voltage Low ISINK = 1mA 0.4 V
IRDY RDY Leakage Current VRDY < 5.5V, VOUT < 98% of VOUT 1.0 μA
OTMP Shutdown Temperature 145 °C
1. The AAT4621 is guaranteed to meet performance specification over the -40°C to 85°C operating temperature range and is assured by design, characterization and correlation
with statistical process controls.
2. For VCC outside this range consult the Typical EN Threshold curve.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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Electrical Characteristics1
VCC = 3.0V to 5.5V, TA = -40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C.
Symbol Description Conditions Min Typ Max Units
AAT4621-1
VCC Operation Voltage 3 5.5 V
IQQuiescent Current ENIL or ENIU = 0V, IOUT = 0; RHYS = 200kΩ40 75 μA
IQ(OFF) Off Supply Current ENIL = ENIU = High, VOUT = Open 0.4 1 μA
ISD(OFF) Off Switch Current ENIL = ENIU = High, VOUT = 0V 0.4 10 μA
VUVLO
Under-Voltage Lockout Rising Edge 2.7 3 V
Hysteresis 120 mV
RDS(ON) On-Resistance VCC = 4.75V, RSETU = RSETL = 0K 50 100 mΩ
VCC = 3.0V, RSETU = RSETL = 0K 65 120
ILIMACC Lower Current Limit Accuracy RSETL = 249KΩ; ΔTA ≤ 25°C 360 400 440 mA
RSETL = 249KΩ340 400 460
ILIMACC Upper Current Limit Accuracy RSETU = 1.24MΩ; ΔTA ≤ 20°C, 1800 2000 2200 mA
RSETU = 1.24MΩ , 1700 2000 2300
ILIM(MIN) Minimum Current Limit 150 mA
VEN(L)
EN Input Low Voltage, VENLU VCC = 3.0 to 5.5V 0.4 V
EN Input Low Voltage, VENLL VCC = 3.0 to 5.5V 0.4 V
VEN(H)
EN Input High Voltage, VENHU VCC = 3.0 to 5.5V 1.4 V
EN Input High Voltage, VENHL VCC = 3.0 to 5.5V 1.4 V
IEN(SINK) EN Input Leakage VEN = 5.5V 1 μA
TDEL(OFF) Turn-Off Delay Time VCC = 5.0V 0.4 1 μs
VRDY System Ready Trip Threshold VOUT Rising, TA = 25°C (VIN = 3.3V) 98 % of VOUT
VRDYHYS System Ready Hysteresis RHYS = 200KΩ200 mV
VRDY(L) System Ready Voltage Low ISINK = 1mA 0.4 V
IRDY RDY_ Leakage Current VRDY < 5.5V, VOUT < 98% Of VOUT 1μA
OTMP Shutdown Temperature Thermal Shutdown Temperature 150 °C
Thermal Shutdown Hysteresis 15
1. The AAT4621 is guaranteed to meet performance specification over the -40°C to 85°C operating temperature range and is assured by design, characterization and correlation
with statistical process controls.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Typical Characteristics
AAT4621 Output Current vs. Output Voltage
(RSETU = 383kΩ, 25°C)
Output Voltage (V)
Output Current (A)
0.00
0.10
0.20
0.30
0.40
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3
VCC = 5V
VCC = 3.3V
AAT4621-1 Output Current vs. Output Voltage
(RSETU = 374KΩ; TA = 25°C)
Output Voltage (V)
Output Current (A)
1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
VCC = 5V
VCC = 3.3V
AAT4621 ILIM vs. RSET
(25°C)
RSET (kΩ)
ILIM (A)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
0 200 400 600 800 1000 1200 1400 1600
VCC = 5V
VCC = 3.3V
AAT4621-1 ILIM vs. RSET
(25°C)
RSET (kΩ)
ILIM (A)
0 200 400 600 800 1000 1200 1400 1600
0
0.5
1
1.5
2
2.5
3
VCC = 3.3V
VCC = 5V
Reverse Off-Switch Current vs. Temperature
(ENIU = ENIL = High; VCC = 0V)
Temperature (°C)
IRSD(OFF) (μA)
0.01
0.1
1
10
100
-40 -20 0 20 40 60 80 100 120
VOUT = 5V
VOUT = 3.3V
Off-Switch Current vs. Temperature
(ENIU = ENIL = High; VOUT = 0V)
Temperature (°C)
ISD(OFF) (μA)
0.01
0.1
1
10
100
-40 -20 0 20 40 60 80 100 120
VCC = 5V
VCC = 3.3V
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Typical Characteristics
Off-Supply Current vs. Temperature
(ENIU = ENIL = VCC; VOUT = Open)
Temperature (°C)
IQ(OFF) (μA)
0.01
0.1
1
10
-40 -20 0 20 40 60 80 100 120
VCC = 3.3V
VCC = 5V
RDS(ON) vs. Input Voltage
(RSET = 0kΩ
Ω
)
Input Voltage (V)
RDS(ON) (m
Ω
)
45
50
55
60
65
70
2.5 3 3.5 4 4.5 5 5.5
RDS(ON) vs. Temperature
(RSET = 0Ω)
Temperature (°C)
RDS(ON) (mΩ)
30
40
50
60
70
80
90
-40 -20 0 20 40 60 80 100
VCC = 3V
VCC = 5V
VRHYS vs. RRHYS
RRHYS (kΩ)
VRHYS (V)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
0 500 1000 1500
AAT4621 ILIM vs. Temperature
(VCC = 4V; VOUT = 3.85V; ENIL = 0V; RSETL = 249kΩ)
Temperature (°C)
ILIM (mA)
185
190
195
200
205
-50 -25 0 25 50 75 100
AAT4621 ILIM vs. Temperature
(VCC = 4V; VOUT = 3.85V; ENIU = 0V; RSETU = 1.3MΩ)
Temperature (°C)
ILIM (mA)
950
960
970
980
990
1000
1010
1020
-50 -25 0 25 50 75 100
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Typical Characteristics
AAT4621-1 ILIM vs. Temperature
(VCC = 5V; VOUT = 4.5V; ENIL = 0V; RSETL = 249kΩ)
Temperature (°C)
ILIM (mA)
-50 -25 0 25 50 75 100
395
400
405
410
415
420
AAT4621-1 ILIM vs. Temperature
(VCC = 5V; VOUT = 4.5V; ENIU = 0V; RSETU = 1.24MΩ)
Temperature (°C)
ILIM (mA)
-50 -25 0 25 50 75 100
1940
1960
1980
2000
2020
2040
2060
2080
2100
Quiescent Current IQ vs. Temperature
(ENIU = 0V; ENIL = VCC; or ENIL = 0V;
ENIU = VCC; VOUT = Open)
Temperature (°C)
IQ (μA)
25
30
35
40
45
50
55
-40 -20 0 20 40 60 80 100 120
VCC = 5V
VCC = 3.3V
VEN(H) and VEN(L) vs. Input Voltage
(ENIU = Open; Vary ENIL; T = 25°C)
Input Voltage (V)
VIH and VIL (V)
0.6
0.7
0.8
0.9
1.0
1.1
2.5 3.5 4.5 5.5 6.5 7.5
VEN(L)
VEN(H)
VEN(H) and VEN(L) vs. Input Voltage
(ENIL = Open; Vary ENIU; T = 25°C)
Input Voltage (V)
VEN(H) and VEN(L) (V)
0.6
0.7
0.8
0.9
1.0
1.1
2.5 3.5 4.5 5.5 6.5 7.5
VEN(H)
VEN(L)
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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Typical Characteristics
Hard Short Circuit
(VCC = 3.3V)
Time (20ms/div)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Output Current (bottom) (A)
0
2
4
0.0
0.5
1.0
1.5
VCC
VOUT
IOUT
Hard Short Circuit
(VCC = 5V)
Time (20ms/div)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Output Current (bottom) (A)
0
2
4
6
0.0
0.5
1.0
1.5
VCC
VOUT
IOUT
Soft Short Circuit with 5Ω Series Impedance
(VCC = 3.3V)
Time (2ms/div)
Input Voltage (V)
Output Voltage (V)
Output Current (A)
3
4
5
6
0.0
0.2
0.4
0.6
VCC
and V
OUT
IOUT
Soft Short Circuit with 5Ω Series Impedance
(VCC = 5V)
Time (2ms/div)
Input Voltage (V)
Output Voltage (V)
Output Current (A)
4
5
6
0.0
0.2
0.4
0.6
0.8
1.0
VCC
and V
OUT
IOUT
Charging Profile
(ILIMIT = 150mA; VCC = 4.5V; CO = 0.55F)
Time (5s/div)
Output Voltage (V)
Output Current (A)
0
2
4
6
0.00
0.05
0.10
0.15
VOUT
IOUT
Charging Profile
(ILIMIT = 1A; VCC = 4.5V; CO = 0.55F)
Time (1s/div)
Output Voltage (V)
Output Current (A)
0
2
4
6
0.0
0.2
0.4
0.6
0.8
1.0
VOUT
IOUT
Thermal Foldback
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Typical Characteristics
GSM900 GPRS Class 12 Transmit
1-Slot Ch975, 33dBm
Time (1ms/div)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Output Current (bottom) (A)
-0.5
0.0
0.5
1.0
1.5
2.0
VCC = 3.83V
IOUT
VOUT
= 3.80V
GSM900 GPRS Class 12 Transmit
2-Slot Ch975, 33dBm
Time (1ms/div)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Output Current (bottom) (A)
-0.5
0.0
0.5
1.0
1.5
2.0
VCC
= 3.83V
IOUT
VOUT
= 3.76V
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
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
threshold is specified by ILIM(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 VCC.
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 VCC 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.
Functional Block Diagram
GND
EN IL
EN IU
ISETU
VCC OUT
ISETL
RDY
RHYS
Reverse
Blocking
Over-Temp
Protection Power
Loop
Under-
Voltage
Lockout
1.2V
Reference
Current Limit
Control
AAT4621
PC Card Current Limit Interface and Capacitor Charger
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RSET Range
(Ω)I
ISET (μA)
ILIM/VISET (A/V) Current Limit Range (A) Current Limit (A)
AAT4621 AAT4621_1 AAT4621 AAT4621_1 AAT4621 AAT4621_1
1.5Meg -750K 1 0.8 1.6 1.2-0.6 2.4 - 1.2 RSET*1*0.8 RSET*1*1.6
750K -375K 2 0.4 0.8 0.6-0.3 1.2 - 0.6 RSET*2*0.4 RSET*2*0.8
375K -187.5K 4 0.2 0.4 0.3-0.15 0.6 -0.3 RSET*4*0.2 RSET*4*0.4
187.5K-93.75K 8 0.1 0.2 0.15-0.075 0.3 - 0.15 RSET*8*0.1 RSET*8*0.2
Table 1: RSET Table.
Application Information
ISETU and ISETL Current Limit Set
The AAT4621/AAT621-1 current limit is set at two differ-
ent 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 RSETU or RSETL 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.
VISET = RSET · IISET = 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 VCC to the output pin with
no current limit.
To activate the upper current level (RSETU) pull EN IU low.
To activate the lower current level (RSETL) pull EN IL low.
If both EN IU and EN IL are pulled low the EN IU current
limit level (RSETU) will be selected.
The AAT4621 has a current limit range from 75mA to
1200mA; the AAT4621-1 has a current limit range from
150mA to 2400mA.
RSETU and RSETL (Ω)
Current Limit (mA)
100 300 500 700 900 1100 1300 1500
0
500
1000
1500
2000
2500
3000
AAT4621-1
AAT4621
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 hysteresis voltage and is equal to the
RHYS source current (1μA) times the RHYS resistance.
VHYST = RHYS · 1µA
= 200kΩ · 1µ
A
= 0.2V
The system ready pin (RDY) is an open drain output 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 100k.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
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Power Loop
The AAT4621 power loop limits the load current in the
event that the device power dissipation becomes exces-
sive. The AAT4621 power loop regulates the die tempera-
ture to 110°C (or 130°C for the AAT4621-1), decreasing
the load current in increments of 1/32 of the current limit
set point when the die temperature reaches 110°C (or
130°C for the AAT4621-1). When the die temperature
exceeds 110°C (or 130°C for the AAT4621-1) it decreas-
es the load current by 1/32 of the current limit set point.
If die temperature is less than 110°C (or 130°C for the
AAT4621-1), 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 (or 130°C for the AAT4621-1).
The delay time between die temperature measurements
varies depending on the load current limit set point. The
delay ranges from 0.5ms for a 75mA (or 150mA for the
AAT4621-1) current limit set point to 4ms for a 1.2A (or
2.4A for the AAT4621-1) current limit set point.
For the condition where there is no current limit set point
(shorting RSETU or RSETL to ground) the soft start incre-
ments the current limit is 1/32 steps of 1.2A (or 2.4A for
the AAT4621-1) until the current reaches 1.2A (or 2.4A
for the AAT4621-1), at which point the power MOSFET
turns on fully. At this point, the current is limited by the
RDS(ON) of the power MOSFET 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.
Short Circuit Protection
The series pass power MOSFET turns off completely after
the output has charged to within 18mV of the input volt-
age. 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 hys-
teresis, the current will immediately attempt to slew
from zero to the final programmed value. The device will
continue to output the current limit as long as the output
is VIN - 18mV or until the die temperature reaches
110°C. If temperature fold-back occurs, then the power
loop will become active.
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 (or 150°C for the
AAT4621-1). After over-temperature shutdown, soft
start is initiated once the die temperature drops to
130°C (or 135°C for the AAT4621-1).
Under-Voltage Shutdown
Under-voltage lockout enables the device at 2.7V typical
with 120mV of hysteresis. The maximum UVLO level is
3.0V.
Digitally Programmed
Soft Start Current Limit
At turn on, the digital soft start increases the load cur-
rent in discrete levels equal to 1/32 of the final pro-
grammed current limit set point from zero to the final
programmed current limit level.
Once the AAT4621 has fully charged the supercap, the
soft start circuit is disabled. The soft start function will
only reactivate under the following conditions:
1. The power source or enable is cycled off and back on
2. The thermal shutdown is activated
3. Switching from ENIU to ENIL or vice versa
4. Following an over-current event.
Reverse Current Blocking
An internal comparator disables the internal pass tran-
sistor when the input voltage is less than the output
voltage blocking any reverse current from the output to
the input.
Evaluation Board
The AAT4621/AAT4621-1 evaluation board schematic is
shown in Figure 2. The AAT4621/AAT4621-1 PCB layout
is shown in Figures 3 and 4.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Layout Guidance
When laying out the PC board, the following layout
guideline should be followed to ensure proper operation
of the AAT4621/AAT4621-1:
1. The exposed pad EP must be reliably soldered to
GND. The exposed thermal pad should be connected
to the board ground plane and Pin 12. The ground
plane should include a large exposed copper pad
under the package with VIAs to all board layers for
thermal dissipation.
2. The power traces, including GND traces and the VCC
trace should be kept short, direct and wide to allow
large current flow. Use several via pads when rout-
ing between layers.
3. The input capacitors (C1) should be connected as
close as possible to VCC (Pins 8, 9, 10, 11) and GND
(Pin 12) to get good power filtering.
4. The output capacitor (C2) should be connected as
close as possible to OUT (Pins 5, 6, 7) and GND (Pin
12) to get good power filtering as the device will
recharge the Supercap when the output voltage level
sensed on the OUT pin is reduced by approximately
18-20mV below its input voltage (VCC) level.
EN IL
J2
EN IU
J1
VCC
P2
GND
P4
GND
P5
RDY
P1
OUT
P3
VCC
VCC
VCC
EN IL
EN IU
RHYS
ISETL
ISETU
OUT
RDY
VCC
200K
R2
1M
R3
120K
R4
LED RED
D1
10µF
C1
10µF
C2
IN
TB1
OUT
TB2
+
+
0.55F
SC1
47.5K
R5
47.5K
R6
1.5K
R1
OUT 5
RDY 1
OUT 6
VCC
10
RHYS 2
ISETU 3
VCC
9
ISETL 4
VCC
11
GND
12
EN IL
13
EN IU
14
OUT 7
VCC
8
AAT4621/AAT4621-1
U1
Figure 2: AAT4621/AAT4621-1 Evaluation Board Schematic.
Figure 3: AAT4621/AAT4621-1 Evaluation Board PCB Top Side.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Figure 4: AAT4621/AAT4621-1 Evaluation Board PCB Bottom Side.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Ordering Information
Package Marking1 Part Number (Tape and Reel)2
TDFN33-14 YWXYY AAT4621IWO-T1
TDFN33-14 K5XYY AAT4621IWO-1-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information3
TDFN33-14
Top View Bottom View
3.000
±
0.050
Index Area
3.000
±
0.050
Detail "A"
1.650
±
0.050
2.500
±
0.050
0.203 REF
0.750
±
0.050
0.000
+
0.100
- 0.000
Detail "A"
Side View
0.425
±
0.050
0.400 BSC
0.180
±
0.050
Pin 1 Indicator
(Optional)
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
AAT4621
PC Card Current Limit Interface and Capacitor Charger
DATA SHEET
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201944A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 15, 2012
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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