AAT1155 SwitchReg step-down switching converter ideal applications whe
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1MHz 2.5A Step-Down DC/DC Converter General Description
AAT1155 SwitchReg step-down switching converter ideal applications where high efficiency, small size, ripple critical. Able deliver 2.5A with internal power MOSFET, current-mode controlled provides high efficiency. Fully internally compensated, AAT1155 simplifies system design lowers external parts count. AAT1155 available Pb-free MSOP-8 package rated over -40°C +85°C temperature range.
AAT1155
SwitchReg
5.5V Supply Input Fixed Adjustable VOUT: 1.0V 4.2V 2.5A Output Current Efficiency Integrated Resistance Power Switches Internally Compensated Current Mode Control 1MHz Switching Frequency Constant Pulse Width Modulation (PWM) Mode Output Ripple with Light Load Internal Soft Start Current Limit Protection Over-Temperature Protection MSOP-8 Package -40°C +85°C Temperature Range
Applications
Cable/DSL Modems Computer Peripherals High Efficiency Conversion from 3.3V Supply Network Cards Set-Top Boxes
Typical Application
INPUT
AAT1155
1.5H
OUTPUT 0.1F 120F
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Descriptions
AAT1155
Symbol
Function
Feedback input pin. Signal ground. Converter enable pin. Small signal filtered bias supply. Input supply converter power stage. Inductor connection pin.
Configuration
MSOP-8
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Absolute Maximum Ratings1
25°C, unless otherwise noted. Symbol
VCC, TLEAD VESD
AAT1155
Description
VCC, Operating Junction Temperature Range Maximum Soldering Temperature leads, sec) Rating2
Value
-0.3 VP+0.3 -0.3 VCC+0.3 -0.3 VCC+0.3 3000
Units
Thermal Characteristics3
Symbol
Description
Maximum Thermal Resistance Maximum Power Dissipation
Value
Units
°C/W
Recommended Operating Conditions
Symbol
Description
Ambient Temperature Range
Rating
Units
Stresses above those listed Absolute Maximum Ratings cause permanent damage device. Functional operation conditions other than operating conditions specified implied. Only Absolute Maximum Rating should applied time. Human body model 100pF capacitor discharged through 1.5k resistor into each pin. Mounted demo board (FR4, still air). 1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Electrical Characteristics
-40°C +85°C, unless otherwise noted. Typical values 25°C. Symbol
VOUT VUVLO VUVLO(HYS) ISHDN ILIM RDS(ON)H VOUT (VOUT*VIN) VOUT/VOUT FOSC THYS
AAT1155
Description
Input Voltage Range Output Voltage Tolerance Input Voltage Input High Voltage Under-Voltage Lockout Under-Voltage Lockout Hysteresis Quiescent Supply Current Shutdown Current Current Limit High Side Switch Resistance Efficiency Load Regulation Line Regulation Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis
Conditions
VOUT 5.5V, IOUT 0.5A
Units
-2.5
Rising Falling Load, 5.5V 25°C 25°C IOUT 1.0A ILOAD 2.5A 2.7V 5.5V 25°C
±2.3 0.75 1000
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics
Efficiency Load Current
(VIN 5.0V; VOUT 3.3V)
AAT1155
RDS(ON) Temperature
2.7V
3.6V
4.2V
Efficiency
RDS(ON)
0.01
5.0V
5.5V
Output Current
Temperature (°C)
Oscillator Frequency Variation Input Voltage
(VOUT 3.3V)
RDS(ON) Input Voltage
(IDS
Variation
0.25
RDS(ON)
-0.25
-0.5
Input Voltage
Input Voltage
Oscillator Frequency Variation Temperature
(VIN
Enable Threshold Input Voltage
Enable Threshold
EN(H)
Variation
EN(L)
Temperature (°C)
Input Voltage
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics
Output Voltage Variation Temperature
(IOUT 3.3V)
Output Voltage Error
AAT1155
Line Regulation
(VOUT 3.3V)
Variation
0.3A
-0.2 -0.4 -0.6 -0.8
3.0A
Temperature (°C)
Input Voltage
AAT1155 Evaluation Board Over-Temperature Current Input Voltage
(VOUT 3.3V)
3.75 4.25 4.75 5.25 -1.0
Load Regulation
(VIN 5.0V; VOUT 3.3V)
Output Current
Output Error
55°C 70°C 85°C 100°C
-2.0 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 -9.0 -10.0 0.01
Input Voltage
Load Current
Non-Switching Operating Current Temperature
Operating Current (mA)
Over-Temperature Shutdown Current Temperature
(VOUT 3.3V; 5.0V)
2.7V
3.6V
4.2V
5.0V
5.5V
Output Current
Temperature (°C)
Temperature (°C)
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics
Enalbe Output Voltage (top trace)
AAT1155
Inrush Output Overshoot Characteristics
0.04 0.02
Tantalum Output Ripple
(IOUT 3.0A; VOUT 3.3V; 5.0V)
Inductor Current (bottom trace)
Inductor Current (bottom)
Output Ripple (top) (mV)
0.00 -0.02 -0.04 -0.06 -0.08 -0.10 -0.12 120F 6.3V Tantalum Vishay 594D127X96R3C2T
Time (ms)
Time
Loop Crossover Gain Phase
Phase 1.5Hy
Output Ripple
(IOUT 3.0A; VOUT 3.3V; 5.0V)
Output Ripple (top) (mV)
200F 6.3V Ceramic C3325X5R0J107M Vishay GRM43SR60J107ME20L
Phase (Degrees)
Inductor Current (bottom)
Gain (dB)
300F gain 100F Ceramic C3225X5R0J107M Vishay GRM43SR60J107ME20L
200F gain
-135
10000
-180 100000
Frequency (Hz)
Time
Loop Crossover Gain Phase
Output Ripple
(IOUT 3.0A; VOUT 3.3V; 5.0V)
Output Ripple (top) (mV)
300F 6.3VCeramic C3325X5R0J107M Vishay GRM43SR60J107ME20L
Inductor Current (bottom)
Phase (Degrees)
Gain (dB)
Gain
120F 6.3V Tantalum Vishay 594D127X96R3C2T 100000
-135 -180 1000000
10000
Frequency (Hz)
Time
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics
Tantalum Transient Response
(IOUT 3.0A; VOUT 3.3V; 5.0V)
3.40 3.30 120F 6.3V Tantalum Vishay 594D127X96R3C2T
3.40 3.30
AAT1155
Transient Response
(IOUT 3.0A; VOUT 3.3V; 5.0V)
100F 6.3V Ceramic C3325X5R0J107M Vishay GRM43SR60J107ME20L
Inductor Current (bottom)
Inductor Current (bottom)
Output Voltage (top) (mV)
Output Voltage (top) (mV)
3.20 3.10 3.00 2.90 2.80 2.70 2.60
3.20 3.10 3.00 2.90 2.80 2.70 2.60
Time
Time
Transient Response
(IOUT 3.0A; VOUT 3.3V; 5.0V)
3.40 3.30
100F 6.3V Ceramic C3325X5R0J107M Vishay GRM43SR60J107ME20L
Inductor Current (bottom)
Output Voltage (top) (mV)
3.20 3.10 3.00 2.90 2.80 2.70 2.60
Time
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Functional Block Diagram
2.5V 5.5V
AAT1155
LOGIC
Temp. Sensing
Applications Information
Main Control Loop
AAT1155 peak current mode step-down converter. inner wide bandwidth loop controls inductor peak current. inductor current sensed flows through internal P-channel MOSFET. fixed slope compensation signal then added sensed current maintain stability duty cycles greater than 50%. inner loop appears voltage-programmed current source parallel with output capacitor. voltage error amplifier output programs current loop necessary inductor current force constant output voltage load line conditions. feedback resistive divider internal, dividing output voltage error amplifier reference voltage 1.0V. error amplifier limited gain. This eliminates need external compensation components, while still providing sufficient loop gain good load regulation. crossover frequency phase margin output capacitor value.
Duty cycle extends 100% input voltage approaches output voltage. Thermal shutdown protection disables device event short-circuit overload condition.
Soft Start/Enable
Soft start controls current limit when input voltage enable applied. limits current surge seen input eliminates output voltage overshoot. When pulled low, enable input forces device into low-power, non-switching state. total input current during shutdown less than 1µA.
Power Signal Source
Separate small signal ground power supply pins isolate internal control circuitry from switching noise. addition, pass filter (shown Figure filters noise associated with power switching.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
2.7V-5.5V VOUT 1.25V 2.5A 2.55k AAT1155-1.0 1.5µH
AAT1155
100µF
100k
10µF 0.1µF 10.0k
B340LA
120µF
Murata 10µF 6.3V GRM42-6X5R106K6.3 Vishay 120µF 6.3V 594D127X96R6R3C2T 0603ZD104M Vishay Sprague 100µF 595D107X0016C 100µF B340LA Diodes Inc. CDRH6D28-1.5µH Sumida Options MuRata 100uF 6.3V GRM43-2 107M 100µF 6.3V (two three parallel) 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two three parallel)
Figure AAT1155 Evaluation Board with Adjustable Output.
Current Limit Over-Temperature Protection
Over-temperature current limit circuitry protects AAT1155 external Schottky diode during overload, short-circuit, excessive ambient temperature conditions. junction over-temperature threshold 140°C nominal 15°C hysteresis. Typical graphs over-temperature load current input voltage ambient temperature shown Typical Characteristics section this document.
peak ripple current Assuming input voltage ripple, output inductance required
VOUT VOUT VIN(MAX) 3.3V 3.3V 2.5A 1MHz 5.25V
1.23H
factor fraction full load (40%) selected ripple current maximum input voltage. corresponding inductor current
IRMS 2.5A
Inductor
output inductor selected limit ripple current full load current maximum input voltage. Manufacturer's specifications list both inductor current rating, which thermal limitation, peak current rating, which determined inductor saturation characteristics. inductor should show appreciable saturation under normal load conditions. During overload short-circuit conditions, inductor exceed peak current rating without affecting converter performance. Some inductors have sufficient peak average current ratings result excessive losses high DCR. losses associated with effect total converter efficiency must considered. 2.5A load ripple current maximum input voltage, maximum peak-to10
peak-to-peak ripple current which fixed inductor selection above. peak-topeak current full load current, peak current full load will 120% full load. 1.5µH inductor selected from Sumida CDRH6D38 series 4.0A current rating with height 4mm. full load, inductor loss 70mW 0.84% loss efficiency.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
Schottky Freewheeling Diode
Schottky average current load current multiplied minus duty cycle.
AAT1155
Surface Mount Schottky Diodes
Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V 0.45 0.46V
Input Capacitor Selection
primary function input capacitor provide impedance loop edges pulsed current drawn AAT1155. ESR/ESL ceramic capacitor ideal this function. minimize stray inductance, capacitor should placed closely possible This also keeps high frequency content input current localized, minimizing radiated conducted while facilitating optimum performance AAT1155. Proper placement input capacitor shown layout Figure Ceramic capacitors ideal. size required will vary depending load, output voltage, input voltage source impedance characteristics. Typical values range from 10µF. input capacitor current varies with input voltage output voltage. highest when input voltage double output voltage where half load current.
IRMS
VOUT 3.3V, average diode current
3.3V 0.85A IAVG 2.5A 5.0V
With 125°C maximum junction temperature 120°C/W thermal resistance, maximum average current
IAVG J(MAX)- 125°C 70°C 1.14A 0.4V
overload, short-circuit, excessive ambient temperature conditions, AAT1155 enters overtemperature shutdown mode protecting AAT1155 well output Schottky. this mode, output current limited internally until junction temperature reaches temperature limit (see over-temperature characteristics graphs). diode reverse voltage must rated withstand input voltage.
3.5V-5.5V
Vout 3.3V 2.5A AAT1155-3.3 1.5µH
100µF
100k
10µF 0.1µF
B340LA
120µF
Murata 10µF 6.3V GRM42-6X5R106K6.3 Vishay120µF 6.3V 594D127X96R6R3C2T 0603ZD104M Vishay Sprague 100µF 595D107X0016C 100µF B340LA Diodes Inc. CDRH6D28-1.5µH Sumida Options MuRata 100µF 6.3V GRM43-2 107M 100µF 6.3V (two three parallel) 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two three parallel)
Figure 3.3V, Output Efficiency.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
high tantalum capacitor with value about times input ceramic capacitor also required when using 10µF smaller ceramic input bypass capacitor. This dampens input oscillations that occur source inductance resonating with converter input impedance. zero associated with tantalum capacitor, smaller values than those required with ceramic capacitors provide more phase margin with greater loop crossover frequency.
AAT1155
Layout
Figures display suggested layout AAT1155. following guidelines should used help ensure proper layout. connection from input capacitor Schottky anode should short possible. input capacitor should connect closely possible (Pins (Pin should connected closely possible. connection from cathode Schottky node should short possible. feedback trace (Pin should separate from power trace connect closely possible load point. Sensing along high-current load trace degrade load regulation. resistance trace from load return (Pin should kept minimum. This will help minimize error regulation differences potential internal reference ground load return. required order provide cleaner power source AAT1155 control circuitry.
Output Capacitor
With external compensation components, output capacitor strong effect loop stability. Larger output capacitance will reduce crossover frequency with greater phase margin. 200µF ceramic capacitor provides sufficient bulk capacitance stabilize output during large load transitions characteristics necessary very output ripple. ripple current given
IRMS (VIN VOUT)
ceramic output capacitor, dissipation current associated output ripple negligible. Tantalum capacitors with sufficiently meet output ripple requirements generally have current rating much greater than that actually seen this application. maximum tantalum output capacitor
VRIPPLE
where peak-to-peak inductor ripple current.
Figure Evaluation Board Side.
Figure Evaluation Board Bottom Side.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
Thermal
Losses associated with AAT1155 output switching MOSFET switching losses conduction losses. conduction losses associated with RDS(ON) characteristics output switching device. full load condition, assuming continuous conduction mode (CCM), accurate calculation RDS(ON) losses derived from following equations:
RMS2 RDS(ON)
AAT1155
Design Example
(see Figures reference) IOUT IRIPPLE VOUT TMAX 2.5A Full Load 2.5V 1MHz 70°C
RDS(ON) losses
Inductor Selection
IRMS
Internal switch current duty cycle forward voltage drop Schottky diode.
VOUT VOUT 3.3V 3.3V 1.23H 2.5A 1MHz 5.25V
standard value 1.5µH Sumida inductor Series CDRH6D38.
peak-to-peak inductor ripple current. simplified form calculating RDS(ON) switching losses given
RDS(ON)
3.3V 3.3V 0.82A 11.5H 1MHz 5.25V
IOUT
2.5A 0.41 2.91A
Efficiency Load Current
(VIN 5.0V; VOUT 3.3V)
where AAT1155 quiescent current. Once total losses have been determined, junction temperature derived. thermal resistance (JA) MSOP-8 package mounted printed circuit board still 150°C/W. TAMB TAMB maximum ambient temperature resultant maximum junction temperature.
Efficiency
0.01
Output Current
Figure Input, 3.3V Output.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
AAT1155 Junction Temperature
RDS(ON) 2.52 3.3V 20ns 1MHz 2.5A
AAT1155
120µF Vishay 594D tantalum capacitor ripple current rating 1.48Arms case size. Although smaller case sizes sufficiently rated this ripple current, their level would result excessive output ripple. requirement tantalum capacitor estimated
0.42 Watts
TJ(MAX) TAMB 70°C 150°C/W 0.42W 133°C
IRMS
VRIPPLE 111m 0.9A
(VOUT (VIN VOUT)
3.65V 240mArms 1.5H 1MHz
Diode
IDIODE 3.3V 0.93A 2.5A 5.25V
0.35V
PDIODE IDIODE
0.35V 0.93A 0.33A
Given ambient thermal resistance 120°C/W from manufacturer's datasheet, TJ(MAX) diode
three 1812 100µF 6.3V ceramic capacitors parallel also provide sufficient phase margin. associated with ceramic capacitors also reduces output ripple significantly over that seen with tantalum capacitors. Temperature rise ripple current dissipation also reduced.
Input Capacitor
input capacitor ripple
J(MAX) 70°C 120°C 0.33W 109°C
IRMS
1.82Arms
Output Capacitor
output capacitor value required sufficient loop phase margin depends type capacitor selected. ceramic capacitor, minimum value 200µF required. tantalum capacitor, lower values acceptable. While relatively higher associated with tantalum capacitor will give more phase margin more dampened transient response, output voltage ripple will higher.
examples shown, ceramic capacitor located closely possible. provides impedance path sharp edges associated with input current. required, depending upon impedance characteristics looking back into source. serves dampen input oscillations that arise from source that highly inductive. most applications, where source sufficient bulk capacitance directly AAT1155 through large traces planes, required. When operating AAT1155 evaluation board bench, required inductance wires running from laboratory power supply evaluation board.
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
Adjustable Output
applications requiring output other than fixed outputs available, version programmed externally. Resistors Figure force output regulate higher than volt. accurate results (less than error outputs), select 10k. Once been selected, calculated. 1.25 volt output with 10k, 2.5k. 0.25 2.5k
AAT1155
Capacitors Part Number
C4532X5ROJ107M GRM43-2 107M GRM43-2 476K GRM42-6 106K 594D127X_6R3C2T 595D107X0016C
Manufacturer
MuRata MuRata MuRata Vishay Vishay
Capacitance (µF)
Voltage
Temp
Case
1812 1812 1812 1206
Inductors Part Number
CDRH6D38-4763-T055 N05D B1R5M NP06DB B1R5M LQH55DN1R5M03 LQH66SN1R5M03
Manufacturer
Sumida Taiyo Yuden Taiyo Yuden MuRata MuRata
Inductance (µH)
(Amps)
0.014 0.025 0.022 0.022 0.016
Height (mm)
Type
Shielded Non-Shielded Shielded Non-Shielded Shielded
Diodes Manufacturer
Diodes Inc. ROHM Micro Semi
Part Number
B340LA RB050L-40 5820SM
0.45V 0.45 0.46V
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter Ordering Information
Output Voltage
1.0V (Adj. VOUT 1.0V) 1.8V 2.5V 3.3V
AAT1155
Package
MSOP-8 MSOP-8 MSOP-8 MSOP-8
Marking1
KXXYY KYXYY ILXYY IKXYY
Part Number (Tape Reel)2
AAT1155IKS-1.0-T1 AAT1155IKS-1.8-T1 AAT1155IKS-2.5-T1 AAT1155IKS-3.3-T1
AnalogicTech products offered Pb-free packaging. term "Pb-free" means semiconductor products that compliance with current RoHS standards, including requirement that lead exceed 0.1% weight homogeneous materials. more information, please visit website
Package Information
MSOP-8
1.95
3.00 0.10
4.90 0.10
0.60 0.20 0.254
0.95
3.00 0.10
0.95 0.15 0.85 0.10
0.075 0.075 0.65 0.30 0.08
dimensions millimeters.
assembly date code. Sample stock generally held part numbers listed BOLD.
GAUGE PLANE
0.155 0.075
1155.2006.09.1.7
1MHz 2.5A Step-Down DC/DC Converter
AAT1155
Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility circuitry other than circuitry entirely embodied AnalogicTech product. circuit patent licenses, copyrights, mask work rights, other intellectual property rights implied. AnalogicTech reserves right make changes their products specifications discontinue product service without notice. Customers advised obtain latest version relevant information verify, before placing orders, that information being relied current complete. products sold subject terms conditions sale supplied time order acknowledgement, including those pertaining warranty, patent infringement, limitation liability. AnalogicTech warrants performance semiconductor products specifications applicable time sale accordance with AnalogicTech's standard warranty. Testing other quality control techniques utilized extent AnalogicTech deems necessary support this warranty. Specific testing parameters each device necessarily performed. AnalogicTech AnalogicTech logo trademarks Advanced Analogic Technologies Incorporated. other brand product names appearing this document registered trademarks trademarks their respective holders.
Advanced Analogic Technologies, Inc.
Arques Avenue, Sunnyvale, 94085 Phone (408) 737-4600 (408) 737-4611
1155.2006.09.1.7
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