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AAT1156
1MHz 700mA Step-Down DC-DC Converter General Description
The AAT1156 SwitchRegTM is a member of AnalogicTechTM's Total Power Management ICTM (TPMICTM) product family. The step-down switching converter is ideal for applications where high efficiency is required over the full range of load conditions. The 2.7V to 5.5V input voltage range makes the AAT1156 ideal for single-cell lithium-ion/polymer battery applications. Capable of more than 700mA with internal MOSFETs, the current-mode controlled IC provides high efficiency over a wide operating range. Fully integrated compensation simplifies system design and lowers external parts count. The AAT1156 is available in the 16-pin 3x3mm QFN package and is rated over the -40C to +85C temperature range.
Features
* * * * * * * * * * * * * * *
SwitchRegTM
VIN Range: 2.7 to 5.5 Volts Up to 95% Efficiency 110m RDS(ON) Internal Switches <1A Shutdown Current 1MHz Step-Down Switching Frequency Fixed or Adjustable VOUT 0.8V Integrated Power Switches Current Mode Operation Internal Compensation Stable with Ceramic Capacitors Internal Soft Start Over-Temperature Protection Current Limit Protection 16-Pin QFN 3x3mm Package -40C to +85C Temperature Range
Applications
* * * * * * Cellular Phones Digital Cameras MP3 Players Notebook Computers PDAs Wireless Notebook Adapters
Typical Application
U1 AAT1156 12 R1 100 C1 10F 11 10 7 9 6 C2 0.1 F 8 5 VP VP VP EN VCC LL NC SGND FB LX LX LX NC PGND PGND PGND 4 15 14 13 16 3 2 1 R4 59k C3, C4 2 x 22F L1 4.7H R3 187k
INPUT
2.5V
(VOUT = 2.5V; L = 4.7H; CDRH3D16)
100 95
AAT1156 Efficiency
VIN = 3.0V VIN = 4.2V VIN = 3.6V
Efficiency (%)
90 85 80 75 70 65 60 55 50 1 10 100 1000
C1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3 C3-C4 MuRata 22F 6.3V GRM21BR60J226ME39L X5R 0805 L1 Sumida CDRH3D16-4R7NC
Output Current (mA)
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Pin Descriptions
Pin #
1, 2, 3 4
Symbol
PGND FB
Function
Main power ground return pin. Connect to the output and input capacitor return. (See board layout rules.) Feedback input pin. This pin is connected to the converter output. It is used to set the output of the converter to regulate to the desired value via an internal resistive divider. For an adjustable output, an external resistive divider is connected to this pin on the 1V model. Signal ground. Connect the return of all small signal components to this pin. (See board layout rules.) Mode selector switch. When pulled low, the device enters light load mode. Enable input pin. A logic high enables the converter; a logic low forces the AAT1156 into shutdown mode, reducing the supply current to less than 1A. The pin should not be left floating. Not internally connected. Bias supply. Supplies power for the internal circuitry. Connect to input power via low pass filter with decoupling to SGND. Input supply voltage for the converter power stage. Must be closely decoupled to PGND. Connect inductor to these pins. Switching node internally connected to the drain of both high- and low-side MOSFETs. Exposed paddle (bottom); connect to PGND directly beneath package.
5 6 7
SGND LL EN
8, 16 9 10, 11, 12 13, 14, 15 EP
NC VCC VP LX
Pin Configuration
QFN33-16 (Top View) LX LX LX NC
16 15 14 13
PGND PGND PGND FB
1 2 3 4 5 6 7 8
12 11 10 9
VP VP VP VCC
NC EN LL SGND
2
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Absolute Maximum Ratings1
Symbol
VCC, V VLX VFB VEN TJ VESD
Description
VCC, VP to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range ESD Rating2 - HBM
Value
6 -0.3 to VP+0.3 -0.3 to VCC+0.3 -0.3 to 6 -40 to 150 3000
Units
V V V V C V
Thermal Characteristics
Symbol
JA PD
Description
Maximum Thermal Resistance (QFN33-16) Maximum Power Dissipation (QFN33-16)4 (TA = 25C)
3
Value
50 2.0
Units
C/W W
Recommended Operating Conditions
Symbol
T
Description
Ambient Temperature Range
Value
-40 to 85
Units
C
1. Stresses above those listed in Absolute Maximum Ratings may cause 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. Human body model is 100pF capacitor discharged through a 1.5k resistor into each pin. 3. Mounted on a demo board (FR4, in still air). 4. Derate 20mW/C above 25C. 1156.2005.11.1.2
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Electrical Characteristics
VIN = VCC = VP = 5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C. Symbol
VIN VOUT VIL VIH VUVLO VUVLO(HYS) IIL IIH IQ ISHDN ILIM
Description
Input Voltage Range Output Voltage Tolerance Input Low Voltage Input High Voltage Under-Voltage Lockout Under-Voltage Lockout Hysteresis Input Low Current Input High Current Quiescent Supply Current
Conditions
VIN = VOUT + 0.2 to 5.5V, IOUT = 0 to 700mA
Min
2.7 -3
Typ
Max
5.5 3 0.6
Units
V % V V V mV A A A A A m m % %/V kHz C C
1.4 VIN Rising, VEN = VCC VIN Falling, VEN = VCC VIN = VFB = 5.5V VIN = VFB = 0V No Load, LL = 0V; VFB = 0V, VIN = 4.2V, TA = 25C VEN = 0V, VIN = 5.5V TA = 25C TA = 25C TA = 25C VIN = 4.2V, ILOAD = 0 to 700mA VIN = 2.7 to 5.5V TA = 25C 2.5 1.2 250 1.0 1.0 350 1.0 1.2 110 100 0.9 0.1 1000 140 15 150 150
220
Shutdown Current Current Limit RDS(ON)H High Side Switch On Resistance RDS(ON)L Low Side Switch On Resistance VOUT(VOUT*VIN) Load Regulation DVOUT/VOUT Line Regulation FOSC Oscillator Frequency TSD Over-Temperature Shutdown Threshold THYS Over-Temperature Shutdown Hysteresis
750
1350
4
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Typical Characteristics
Output Ripple
(0.8V; 10mA; VIN = 3.6V) Enable and Output Voltage (top) (V)
20 1.4 1.2 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2
Soft Start
(0.8V; 700mA; VIN = 3.6V)
3.5 3
Output Voltage (AC coupled) (top) (mV)
10 0 -10 -20 -30 -40 -50 -60
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
1 0.8 0.6 0.4 0.2 0 -0.2
2.5 2 1.5 1 0.5 0 -0.5
Time (2s/div)
Time (100s/div)
Output Ripple
(0.8V; 700mA; VIN = 3.6V)
20 3.5 3 4.4 4.2
Line Transient
(IOUT = 500mA; VO = 0.8V) Output Voltage (AC coupled) (bottom) (mV)
60 50 40 30 20 10 0 -10 -20
Output Voltage (AC coupled) (top) (mV)
10 0 -10 -20 -30 -40 -50 -60
Inductor Current (bottom) (A)
Input Voltage (top) (V)
2.5 2 1.5 1 0.5 0 -0.5
4 3.8 3.6 3.4 3.2 3 2.8
Time (250ns/div)
Time (20sec/div)
Load Transient Response
(50mA-680mA; VIN = 3.6V; VOUT = 0.8V)
0.83 0.81
No Load Supply Current vs. Input Voltage
300
Inductor and Load Current (bottom) (500mA/div)
Supply Current (A)
250 200 150
85C
Output Voltage (top) (20mV/div)
0.79 0.77 0.75 0.73 0.71 0.69 0.67
25C -40C
O O Time (10sec/div)
100 50 0 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Typical Characteristics
Output Voltage vs. Temperature
(VIN = 4.2V; VOUT = 0.8V; 400mA VOUT)
0.1
DC Regulation
(VOUT = 0.6V)
3.0 2.0 1.0 0.0
Output Voltage Error (%)
Output Error (%)
0.0 -0.1 -0.2 -0.3 -0.4 -40
VIN = 4.2V VIN = 3.6V
-1.0
VIN = 2.7V
-2.0 -3.0
-20
0
20
40
60
80
100
0.0001
0.001
0.01
0.1
1
Temperature (C)
Output Current (A)
Frequency vs. Temperature
(VIN = 3.6V)
1.2 200 180 160
P-Channel RDSON vs. Input Voltage
Frequency (MHz)
1.1 1 0.9 0.8 0.7 0.6 -40 -20 0 20 40 60 80 100
100C
120C
RDSON (m)
140 120 100 80 60 40 20 0 2.5 3 3.5 4 4.5 5 5.5
85C
25C
Temperature (C)
Input Voltage (V)
Frequency vs. Input Voltage
1.02 1.01 200 180 160
N-Channel RDSON vs. Input Voltage
Frequency (MHz)
1 0.99 0.98 0.97 0.96 0.95 0.94 2.7 3.2 3.7 4.2 4.7 5.2 5.7
100C
120C
RDSON (m)
140 120 100 80 60 40 20 0 2.5 3 3.5 4 4.5 5 5.5
85C
25C
Input Voltage (V)
Input Voltage (V)
6
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Functional Block Diagram
VCC
VP= 2.7V to 5.5V
1.0V REF
FB
OP. AMP
CMP
DH
LOGIC
LX
1M
DL Temp. Sensing
OSC
SGND
EN
LL
PGND
Operation
Control Loop
The AAT1156 is a peak current mode step-down converter. The inner, wide bandwidth loop controls the inductor peak current. The inductor current is sensed through the P-channel MOSFET (high side) and is also used for short-circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The loop appears as a voltage-programmed current source in parallel with the output capacitor. The voltage error amplifier output programs the current loop for the necessary inductor current to force a constant output voltage for all load and line conditions. The external voltage feedback resistive divider divides the output voltage to the error amplifier reference voltage of 0.6V. The voltage error amplifier DC gain is limited. This eliminates the need for external compensation components, while
still providing sufficient DC loop gain for good load regulation. The voltage loop crossover frequency and phase margin are set by the output capacitor.
Soft Start/Enable
Soft start increases the inductor current limit point in discrete steps once the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1156 into a non-switching shutdown state. The total input current during shutdown is less than 1A.
Power and Signal Source
Separate small signal ground and power supply pins isolate the internal control circuitry from the noise associated with the output MOSFET switching. The low pass filter R1 and C2 (shown in the schematic in Figure 1) filters the input noise associated with the power switching.
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AAT1156
1MHz 700mA Step-Down DC-DC Converter
Enable Vin+ 12 R1 100 R2 C1 10F 100K C2 0.1 F 11 10 7 9 6 R6 8 100k 5 VP VP VP EN VCC LL N/C SGND
U1 AAT1156 FB LX LX LX N/C PGND PGND PGND 4 15 14 13 16 3 2 1 R4 59k L1 4.7H R3 200k
Vout+
C3, C4 2 x 22F
LL
C1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3 C3, C4 MuRata 22F 6.3V GRM21BR60J226ME396 X5R 0805 L1 Sumida CDRH3D16-4R7NC
Figure 1: AAT1156 Evaluation Board Schematic--Lithium-Ion to 2.5V Converter.
Current Limit and Over-Temperature Protection
For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140C with 15C of hysteresis.
L= L=
V VOUT 1 - OUT IO k F VIN 1.5V 1.5V 10.7A 0.4 1MHz 4.2V
L = 3.44H
The factor "k" is the fraction of full load selected for the ripple current at the maximum input voltage. For ripple current at 40% of the full load current, the peak current will be 120% of full load. Selecting a standard value of 3.3H gives 42% ripple current. A 3.3H inductor selected from the Sumida CDRH3D16 series has a 63m DCR and a 1.1A DC current rating. At full load, the inductor DC loss is 31mW which amounts to less than 3% loss in efficiency for a 0.7A, 1.5V output.
Inductor
The output inductor is selected to limit the ripple current to a predetermined value, typically 20% to 40% of the full load current at the maximum input voltage. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. For a 0.7A, 1.5V output with the ripple set to 40% at a maximum input voltage of 4.2V, the maximum peak-to-peak ripple current is 280mA. The inductance value required is 3.44H.
Input Capacitor
The primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current drawn by the AAT1156. A low ESR/ESL ceramic capacitor is ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing radiated and conducted EMI while facilitating optimum performance of the AAT1156. Ceramic X5R or X7R capacitors are ideal for this function. The size required will vary depending on
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AAT1156
1MHz 700mA Step-Down DC-DC Converter
the load, output voltage, and input voltage source impedance characteristics. Values range from 1F to 10F. The input capacitor RMS current varies with the input voltage and output voltage. The equation for the RMS current in the input capacitor is: VO VO 1VIN VIN For an X7R or X5R ceramic capacitor, the ESR is so low that dissipation due to the RMS current of the capacitor is not a concern. Tantalum capacitors with sufficiently low ESR to meet output voltage ripple requirements also have an RMS current rating well beyond that actually seen in this application.
IRMS = IO
Layout
Figures 2 and 3 display the suggested PCB layout for the AAT1156. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C1) should connect as closely as possible to VP (Pins 10, 11, and 12) and PGND (Pins 1, 2, and 3). 2. C3, C4, and L1 should be connected as closely as possible. The connection from L1 to the LX node should be as short as possible. 3. The feedback trace (Pin 4) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. 4. The resistance of the trace from the load return to the PGND (Pins 1, 2, and 3) should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. 5. Low pass filter R1 and C2 provide a cleaner bias source for the AAT1156 active circuitry. C2 should be placed as closely as possible to SGND (Pin 5) and VCC (Pin 9).
The input capacitor RMS ripple current reaches a maximum when VIN is two times the output voltage, where it is approximately one half of the load current. Losses associated with the input ceramic capacitor are typically minimal and are not an issue. Proper placement of the input capacitor is shown in the reference design layout in Figure 2.
Output Capacitor
Since there are no external compensation components, the output capacitor has a strong effect on loop stability. Larger output capacitance will reduce the crossover frequency with greater phase margin. For the 1.5V, 0.7A design using the 3.3H inductor, two 22F capacitors provide a stable output. In addition to assisting in stability, the output capacitor limits the output ripple and provides holdup during large load transitions. The output capacitor RMS ripple current is given by:
1 2 3 VOUT (VIN - VOUT) L F VIN
IRMS =
Figure 2: QFN Evaluation Board Top Side.
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Figure 3: QFN Evaluation Board Bottom Side. 9
AAT1156
1MHz 700mA Step-Down DC-DC Converter
Thermal Calculations
There are three types of losses associated with the AAT1156: MOSFET switching losses, conduction losses, and quiescent current losses. The conduction losses are due to the RDS(ON) characteristics of the internal Pand N-channel MOSFET power devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the total losses is given by:
P=
IO2 (RDSON(HS) VO + RDSON(LS) (VIN - VO)) + (tsw F IO VIN + IQ) VIN VIN
where IQ is the AAT1156 quiescent current. Once the total losses have been determined, the junction temperature can be derived from the JA for the QFN33-16 package.
TJ = P * JA + TAMB
Adjustable Output
Resistors R3 and R4 of Figure 1 force the output to regulate higher than 0.6V. The optimum value for R4 is 59k. Values higher than this may cause problems with stability, while lower values can degrade light load efficiency. For a 2.5V output with R4 set to 59k, R3 is 187k.
VO 2.5V R3 = V -1 * R4 = 0.6V - 1 * 59k = 187k REF
500 450 400 350
R4=59k
R3 (k)
300 250 200 150 100 50 0 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Output Voltage (V)
Figure 4: R3 vs. VOUT for Adjustable Output Using the AAT1156.
10
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Design Example
Specifications
IOUT VOUT VIN FS TAMB 0.7A IRIPPLE 40% of Full Load at Max VIN 2.5V 2.7V to 4.2V (3.6V nominal) 1MHz 85C
Maximum Input Capacitor Ripple:
IRMS = I O * V V O * 1 - O = 0.34Arms, VIN = 2 x VO VIN VIN
P = esr * IRMS2 = 5m * 0.342 A = 0.6mW
Inductor Selection:
L=
V VOUT 2.5V 2.5V 1 - OUT = 1= 4.82H IO k F VIN 0.7A 0.3 1MHz 4.2V
Select Sumida inductor CDRH3D16 or CDRH4D28 4.7H. 2.5V VO V 2.5V 1- O = 1= 220mA L F VIN 4.7H 1MHz 4.2V
I =
IPK = IOUT +
I = 0.7A + 0.11A = 0.81A 2
P = IO2 DCR = (0.7A)2 80m = 40mW
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AAT1156
1MHz 700mA Step-Down DC-DC Converter
Output Capacitor Ripple Current:
IRMS = VOUT * (VIN - VOUT) 1 2.5V * (4.2V - 2.5V) * = 62mArms = L * F * VIN 2 * 3 4.7H * 1MHz * 4.2V 2* 3 1 *
Pesr = esr * IRMS2 = 5m * (62 mA)2 = 19W
AAT1156 Dissipation:
IO2 * (RDSON(HS) * VO + RDSON(LS) * (VIN -VO)) VIN
PTOTAL =
+ (tsw * F * IO + IQ) * VIN
=
(0.7A)2 * (0.17 * 2.5V + 0.16 * (4.2V - 1.5V))
4.2V
+ (20nsec * 1MHz * 0.7A + 300A) * 4.2V = 0.141W
TJ(MAX) = TAMB + JA * PLOSS = 85C + 50C/W * 0.141W = 92C
INPUT 12 R1 100 C1 10F 11 10 7 9 6 C2 0.1 F 8 5 VP VP VP EN VCC LL N/C
U1 AAT1156 FB LX LX LX N/C PGND PGND PGND 4 15 14 13 16 3 2 1 R4 59k L1 2.2H R3 19.6k
0.8V
(VOUT = 0.8V; L = 2.2H; CDRH3D16)
100 90
AAT1156 Efficiency
Efficiency (%)
80 70 60 50 40 30
VIN = 2.7V VIN = 4.2V VIN = 3.6V
C3, C4 2 x 22F
SGND
C1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3 C3, C4 MuRata 22F 6.3V GRM21BR60J226ME39L X5R 0805 L1 Sumida CDRH3D16-2R2NC
20 1 10 100 1000
Output Current (mA)
Figure 5: 0.8V Solution.
12
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Surface Mount Inductors
Manufacturer
TaiyoYuden Toko Sumida Sumida Sumida Sumida Sumida Sumida MuRata MuRata
Part Number
NPO5DB4R7M A914BYW-3R5M-D52LC CDRH4D28-4R7 CDRH3D16-2R2 CDRH3D16-3R3 CDRH3D16-4R7 CDRH5D28-4R2 CDRH5D18-4R1 LQH55DN4R7M03 LQH66SN4R7M03
Value
4.7H 3.5H 4.7H 2.2H 3.3H 4.7H 4.2H 4.1H 4.7H 4.7H
Max DC Current
1.4A 1.34A 1.32A 1.2A 1.1A 0.9 2.2A 1.95A 2.7A 2.2A
DCR
0.038 0.073 0.072 0.050 0.063 0.080 0.031 0.057 0.041 0.025
Size (mm) LxWxH
5.9x6.1x2.8 5.0x5.0x2.0 4.7x4.7x3.0 3.8x3.8x1.8 3.8x3.8x1.8 3.8x3.8x1.8 5.7x5.7x3.0 5.7x5.7x2.0 5.0x5.0x4.7 6.3x6.3x4.7
Type
Shielded Shielded Shielded Shielded Shielded Shielded Shielded Sielded Non-Shielded Shielded
Surface Mount Capacitors
Manufacturer
MuRata MuRata MuRata
Part Number
GRM40 X5R 106K 6.3 GRM42-6 X5R 106K 6.3 GRM21BR60J226ME39L
Value
10F 10F 22F
Voltage
6.3V 6.3V 6.3V
Temp. Co.
X5R X5R X5R
Case
0805 1206 0805
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AAT1156
1MHz 700mA Step-Down DC-DC Converter Ordering Information
Output Voltage
0.6V (Adj VOUT 0.8V)
Package
QFN33-16
Marking1
LUXYY
Part Number (Tape and Reel)2
AAT1156IVN-T1
Package Information
Pin 1 Identification
1
0.230 0.05
5
3.000 0.05
Pin 1 Dot By Marking
0.400 0.05
13 9
3.000 0.05
0.500 0.05
Top View
Bottom View
1.55 0.15 0.025 0.025 0.203 0.0254
Side View
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. Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 14
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0.850 0.05

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