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AAT4285
12V Slew Rate Controlled Load Switch General Description
The AAT4285 SmartSwitch is a P-channel MOSFET power switch designed for high-side load switching applications. The MOSFET operates from a 3.0V to 13.2V input range making it ideal for applications in single or dual cell Lithium-Ion battery systems. The device has a typical RDS(ON) of 240m at 12V, allowing a low forward voltage drop and high current handling capability. The device is a slew rate limited turnon load switch and is functionally compatible with the AAT4250 and AAT4280 products, while offering a high operating voltage. The AAT4285 features fast load switch turn-on capability of 100s and offers a shutdown load discharge circuit to rapidly turn off a load circuit when the switch is disabled. The quiescent supply current is very low, typically 25A. The AAT4285 is available in a Pb-free, 8-pin SC70JW package and is specified over the -40C to +85C temperature range.
Features
* *
SmartSwitchTM
* * *
* * *
VIN Range: 3.0V to 13.2V Low RDS(ON) -- 240m typical @ 12V -- 310m Typical at 5V 100s Slew Rate Turn-on Time Fast Shutdown Load Discharge Low Quiescent Current -- Typically 25A -- 1A Maximum in Shutdown TTL/CMOS Input Logic Level Temperature Range: -40C to +85C 8-pin SC70JW Package
Applications
* * * * 2 Cell Lithium-Ion Batteries Camcorders Handheld Test Equipment Load Switching
Typical Application
VIN
IN IN C IN 1F ON ON/OFF GND x 4
OUT
V OUT
AAT4285
C OUT 0.1F
GND
GND
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AAT4285
12V Slew Rate Controlled Load Switch Pin Descriptions
Pin #
1,2 3 4 5, 6, 7, 8
Symbol
IN OUT ON/OFF GND
Function
P-channel MOSFET source. Bypass to ground through a 1F capacitor. P-channel MOSFET drain connection. Bypass to ground through a 0.1F capacitor. Active high enable input. A logic low turns the switch off and the device consumes less than 1A of current. Logic high resumes normal operation. Ground connection
Pin Configuration
SC70JW-8 (Top View)
IN IN OUT ON/OFF
1 2 3 4
8 7 6 5
GND GND GND GND
2
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AAT4285
12V Slew Rate Controlled Load Switch Absolute Maximum Ratings1
Symbol
VIN VON VOUT IMAX IDM TJ
Description
IN to GND ON/OFF to GND OUT to GND Maximum Continuous Switch Current Maximum Pulsed Current Operating Junction Temperature Range
Value
-0.3 to 14 -0.3 to 14 -0.3 to VIN + 0.3 1.7 3.4 -40 to 150
Units
V V V A A C
Thermal Characteristics2
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation
Value
140 714
Units
C/W mW
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. 4285.2007.04.1.0
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AAT4285
12V Slew Rate Controlled Load Switch Electrical Characteristics1
VIN = 12V, TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol
VIN VUVLO VUVLO(hys) IQ IQ(OFF) ISHD RDS(ON) TCRRDS TD(ON) TON TD(OFF) RPD VON(L) VON(H) ION
Description
Conditions
Min
3.0
Typ
2.7 250 25 0.1 240 310 380 2800 20 100 1 520
Max
13.2 3.0 50 1.0 1.0 400 500
Units
V V V A A A m
Operation Voltage Under-Voltage Lockout Under-Voltage Lockout Hysteresis Quiescent Current ON/OFF = Active, IOUT = 0 Off Supply Current ON/OFF = Inactive, OUT = Open Off Switch Current ON/OFF = GND, VOUT = 0 VIN = 12V On Resistance VIN = 5V VIN = 3.3V On Resistance Temperature Coefficient Output Turn-On Delay Time2 RLOAD = 20, TA = 25C Turn-On Rise Time2 RLOAD = 20, TA = 25C Output Turn-Off Delay Time2 RLOAD = 20, TA = 25C Output Pull-Down Resistance ON/OFF Inactive, TA = 25C During OFF ON/OFF Input Logic Low Voltage VIN = 3V to 13V ON/OFF Input Logic High Voltage VIN = 3V to 13V ON/OFF Leakage Current VON/OFF = 13V
ppm/C 40 250 10 800 0.4 s s s V V A
1.6 -1.0
1.0
1. The AAT4285 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Contact factory for other turn-on and delay options.
4
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AAT4285
12V Slew Rate Controlled Load Switch Typical Characteristics
Quiescent Current vs. Temperature
30 35
Quiescent Current vs. Input Voltage
Quiescent Current (A)
Quiescent Current (A)
85
25 20 15 10 5
30 25 20 15 10 5 0
VIN = 12V VIN = 5V VIN = 4.2V
VIN = 3.3V
0 -40 -15 10 35 60
0
2
4
6
8
10
12
14
Temperature (C)
Input Voltage (V)
RDS(ON) vs. Temperature
500 450 400
RDS(ON) vs. Input Voltage
420
VIN = 4.2V
RDS(ON) (m)
350 300 250 200 150 100 -40 -15 10 35 60 85
RDS(ON) (m)
VIN = 3.3V
380
0.1A
340 300 260 220 3 4 5 6 7 8 9 10 11 12
0.5A 2A 1A
VIN = 5V
VIN = 12V
Temperature (C)
Input Voltage (V)
ON/OFF Threshold Low vs. Input Voltage
0.95
ON/OFF Threshold High vs. Input Voltage
1.05
ON/OFF Threshold (V)
0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 3 5
-40C
ON/OFF Threshold (V)
1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65
-40C
25C
7 9
85C
11 13
25C
85C
3
5
7
9
11
13
Input Voltage (V)
Input Voltage (V)
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AAT4285
12V Slew Rate Controlled Load Switch Typical Characteristics
Output Pull-Down Resistance vs. Temperature
800 750
Turn-On
(VIN = 12V; 600mA Load)
VIN = 4.2V VIN = 3.3V
Resistance ()
700 650 600 550 500 450 400 -40
ON/OFF (5V/div)
VOUT (5V/div) VIN = 5V
-15 10 35
VIN = 12V
60 85
IOUT (500mA/div)
Temperature (C)
Time (25s/div)
Turn-Off
(VIN = 12V; 600mA Load) ON/OFF (5V/div) VOUT (5V/div) IOUT (500mA/div)
Time (10s/div)
6
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AAT4285
12V Slew Rate Controlled Load Switch Functional Block Diagram
IN
UnderVoltage Lockout Level Shift Turn-On Slew Rate Control
OUT
ON/OFF
GND GND GND GND
Functional Description
The AAT4285 is a slew rate controlled P-channel MOSFET power switch designed for high-side load switching applications. The device operates with input voltages ranging from 3.0V to 13.2V, making it ideal for single- or multi-cell battery-powered applications. In cases where the input voltage drops below 3.0V, the AAT4285 MOSFET is protected from entering the saturated region of operation by automatically shutting down. In addition, the TTL compatible ON/OFF pin makes the AAT4285 an ideal level-shifted load switch. The slew rate controlling feature eliminates inrush current when
the MOSFET is turned on, allowing the AAT4285 to operate with a small input capacitor, or no input capacitor at all. During slewing, the current ramps linearly until it reaches the level required for the output load condition. The proprietary control method works by careful control and monitoring of the MOSFET gate voltage. When the device is switched ON, the gate voltage is quickly increased to the threshold level of the MOSFET. Once at this level, the current begins to slew as the gate voltage is slowly increased until the MOSFET becomes fully enhanced. Once it has reached this point, the gate is quickly increased to the full input voltage and RDS(ON) is minimized.
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AAT4285
12V Slew Rate Controlled Load Switch Applications Information
Input Capacitor
A 1F or larger capacitor is typically recommended for CIN in most applications. A CIN capacitor is not required for basic operation. However, CIN is useful in preventing load transients from affecting upstream circuits. CIN should be located as close to the device VIN pin as practically possible. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN. However, for higher current operation, ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources, such as batteries in portable devices. itor is highly recommended. A larger value of CIN with respect to COUT will affect a slower CIN decay rate during shutdown, thus preventing VOUT from exceeding VIN. In applications where there is a greater danger of VOUT exceeding VIN for extended periods of time, it is recommended to place a Schottky diode from IN to OUT (connecting the cathode to IN and anode to OUT). The Schottky diode forward voltage should be less than 0.45V.
Thermal Considerations and High Output Current Applications
The AAT4285 is designed to deliver a continuous output load current. The limiting characteristic for maximum safe operating output load current is package power dissipation. In order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account. The following discussions will assume the load switch is mounted on a printed circuit board utilizing the minimum recommended footprint, as stated in the Layout Considerations section of this datasheet. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation:
TJ(MAX) - TA JA
Output Capacitor
For proper slew operation, a 0.1F capacitor or greater between OUT and GND is recommended. The output capacitor has no specific capacitor type or ESR requirement. If desired, COUT may be increased without limit to accommodate any load transient condition without adversely affecting the device turn-on slew rate time.
Enable Function
The AAT4285 features an enable / disable function. This pin (ON/OFF) is compatible with both TTL and CMOS logic.
PD(MAX) =
Reverse Output-to-Input Voltage Conditions and Protection
Under normal operating conditions, a parasitic diode exists between the output and input of the load switch. The input voltage should always remain greater than the output load voltage, maintaining a reverse bias on the internal parasitic diode. Conditions where VOUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into the OUT pin and possibly damage the load switch. In applications where there is a possibility of VOUT exceeding VIN for brief periods of time during normal operation, the use of a larger value CIN capac-
Constants for the AAT4285 are maximum junction temperature, TJ(MAX) = 125C, and package thermal resistance, JA = 140C/W. Worst case conditions are calculated at the maximum operating temperature where TA = 85C. Typical conditions are calculated under normal ambient conditions where TA = 25C. At TA = 85C, PD(MAX) = 286mW. At TA = 25C, PD(MAX) = 714mW. The maximum continuous output current for the AAT4285 is a function of the package power dissipation and the RDS of the MOSFET at TJ(MAX). The maximum RDS of the MOSFET at TJ(MAX) is calculated by increasing the maximum room temperature RDS by the RDS temperature coefficient. The temperature coefficient (TCRRDS) is 2800ppm/C. Therefore,
MAX RDS125C = RDS25C * (1 + TCRRDS * T) MAX RDS125C = 240m * (1 + 0.0028 * (125C - 25C)) = 307m
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AAT4285
12V Slew Rate Controlled Load Switch
For maximum current, refer to the following equation:
PD(MAX) RDS
The power dissipation for a 100mA load is calculated as follows:
IOUT(MAX) <
For example, if VIN = 12V, RDS(MAX) = 307m and TA = 25C, IOUT(MAX) = 1.53A. If the output load current were to exceed 1.53A or if the ambient temperature were to increase, the internal die temperature would increase, and the device would be damaged. Higher peak currents can be obtained with the AAT4285. To accomplish this, the device thermal resistance must be reduced by increasing the heat sink area or by operating the load switch in a duty cycled manner.
PD(MAX) = IOUT2 * RDS PD(100mA) = (100mA)2 * 307m PD(100mA) = 3.07mW PD(90%D/C) = %DC * PD(100mA) PD(90%D/C) = 0.90 * 3.07mW PD(90%D/C) = 2.76mW
The power dissipation for 100mA load at 90% duty cycle is 2.76mW. Now the power dissipation for the remaining 10% of the duty cycle at 2A is calculated:
High Peak Output Current Applications
Some applications require the load switch to operate at a continuous nominal current level with short duration, high-current peaks. The duty cycle for both output current levels must be taken into account. To do so, first calculate the power dissipation at the nominal continuous current level, and then add in the additional power dissipation due to the short duration, high-current peak scaled by the duty factor. For example, a 12V system using an AAT4285 operates at a continuous 100mA load current level and has short 2A current peaks. The current peak occurs for 500s out of a 5ms period. First, the current duty cycle is calculated:
x 500s % Peak Duty Cycle = 100 = 5.0ms % Peak Duty Cycle = 10%
PD(MAX) = IOUT2 * RDS PD(2A) = (2A)2 * 307m PD(2A) = 1.23W PD(10%D/C) = %DC * PD(2A) PD(10%D/C) = 0.10 * 1.23mW PD(10%D/C) = 123mW
The power dissipation for 2A load at 10% duty cycle is 123mW. Finally, the two power figures are summed to determine the total true power dissipation under the varied load.
PD(TOTAL) = PD(100mA) + PD(2A) PD(TOTAL) = 2.76mW + 123mW PD(TOTAL) = 125.76mW
The load current is 100mA for 90% of the 5ms period and 2A for 10% of the period. De-rated for temperature:
The maximum power dissipation for the AAT4285 operating at an ambient temperature of 85C is 286mW. The device in this example will have a total power dissipation of 123mW. This is well within the thermal limits for safe operation of the device; in fact, at 85C, the AAT4285 will handle a 2A pulse for up to 23% duty cycle. At lower ambient temperatures, the duty cycle can be further increased.
240m * (1 + 0.0028 * (125C - 25C)) = 307m
Printed Circuit Board Layout Recommendations
For proper thermal management and to take advantage of the low RDS(ON) of the AAT4285, a few circuit board layout rules should be followed: VIN
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AAT4285
12V Slew Rate Controlled Load Switch
and VOUT should be routed using wider than normal traces, and GND should be connected to a ground plane. To maximize package thermal dissipation and power handling capacity of the AAT4285 SC70JW-8 package, the ground plane area connected to the ground pins should be made as large as possible. For best performance, CIN and COUT should be placed close to the package pins.
Evaluation Board Layout
The AAT4285 evaluation board layout follows the printed circuit board layout recommendations and can be used for good application guide. Refer to Figures 1 through 3. Note: Board layout shown is not to scale.
Figure 1: AAT4285 Evaluation Board Component Side Layout and Silk Screen.
Figure 2: AAT4285 Evaluation Board Solder Side Layout.
VOUT
VIN
1 2 3
R1 100K C1 1F
4
IN IN OUT EN AAT4285
GND GND GND GND
8 7 6 5
C2 0.1F
JP1 ON/OFF
C1 1F X7R 16V 0805 GRM21BR71C105KA01 (C1 1F X5R 16V 0603 GRM188R61C105KA93) C2 0.1F X5R 16V 0805 GRM219R71C104KA01 (C2 0.1F X7R 16V 0603 GRM188R71C104KA01)
Figure 3: AAT4285 Evaluation Board Circuit Schematic Diagram. 10
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AAT4285
12V Slew Rate Controlled Load Switch Ordering Information
Package
SC70JW-8
Marking1
UAXYY
Part Number (Tape and Reel)2
AAT4285IJS-3-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Package Information
SC70JW-8
0.50 BSC 0.50 BSC 0.50 BSC
1.75 0.10
0.225 0.075 2.00 0.20
2.20 0.20
0.048REF
0.85 0.15
1.10 MAX
0.15 0.05
0.100
7 3
0.45 0.10 2.10 0.30
4 4
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611
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