850kHz Synchronous Buck DC/DC Converter General Description AAT11
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AAT1152
850kHz Synchronous Buck DC/DC Converter General Description
AAT1152 SwitchRegis member AnalogicTech's Total Power Management IC(TPMICTM) product family. step-down switching converter ideal applications where high efficiency, small size, ripple critical. Able deliver with internal power MOSFETs, current-mode controlled provides high efficiency using synchronous rectification. Fully internally compensated, AAT1152 simplifies system design lowers external parts count. AAT1152 features Power Good (POK) function which monitors output, alerting system output voltage falls regulation. AAT1152 available MSOP-8 package rated over -40°C 85°C temperature range.
SwitchReg
5.5V Supply Input Fixed Adjustable VOUT 1.0V 4.2V Output Current Integrated Resistance Power Switches Synchronous Rectification Efficiency Power Good Signal Internally Compensated Current Mode Control High Initial Accuracy: 850kHz Switching Frequency Constant 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
100k
10µF
AAT1152
4.1µH
ENABLE OUTPUT SGND 0.1µF PGND 22µF
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Descriptions
Symbol
SGND PGND
Function
Feedback input pin. Signal ground. Converter enable pin. Small signal filtered bias supply. Input supply converter power stage. Inductor connection pin. Power Good indicator. Open-drain output when VOUT falls regulation. Power ground return output stage.
Configuration
MSOP-8
SGND
PGND
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Absolute Maximum Ratings
25°C, unless otherwise noted. Symbol
VCC, VEN, VPOK TLEAD VESD
Description
VCC, POK, Operating Junction Temperature Range Maximum Soldering Temperature leads, sec) Rating
Value
-0.3 VP+0.3 -0.3 VCC+0.3 -0.3 3000
Units
Note: 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. Note Human body model 100pF capacitor discharged through 1.5K resistor into each pin.
Thermal Characteristics
Symbol
Description
Maximum Thermal Resistance (MSOP-8) Maximum Power Dissipation (MSOP-8)
Value
Units
°C/W
Note Mounted demo board.
Recommended Operating Conditions
Symbol
Description
Ambient Temperature Range
Rating
Units
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Electrical Characteristics
-40°C 85°C, unless otherwise noted. Typical values 25°C. Symbol
VOUT ILIM VOUT (VOUT*VIN) VOUT/VOUT FOSC RDSON(H) RDSON(L) VEN(H) VEN(L) VUVLO VUVLO(hys) THYS ISHDN VTH(POK) RPOK
Description
Operation Voltage Output Voltage Tolerance Current Limit Quiescent Supply Current Load Regulation Line Regulation Oscillator Frequency High-Side Switch Resistance Low-Side Switch Resistance Enable Input High Voltage Enable Input Voltage Enable Leakage Current Under-Voltage Lockout
Conditions
25°C Full Temp
-1.0 -2.0
+1.0 +2.0
Units
IOUT 500mA
25°C Load, 4.2V, ILOAD 2.7V 5.5V 25°C 25°C 25°C 2.7V 5.5V 2.7V 5.5V 5.5V Rising Falling
1000
Under-Voltage Lockout Hysteresis Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Shutdown Current 5.5V Ramping Power Good Threshold Ramping Down Power Good Pull-Down Resistance
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Typical Characteristics
High Side RDS(ON) Temperature
Side RDS(ON) Temperature
3.6V 2.7V RDS(ON)
RDS(ON)
3.6V 2.7V 5.5V 4.2V
4.2V
5.5V
Temperature (°C)
Temperature (°C)
RDS(ON) Input Voltage
Enable Threshold Input Voltage
Enable Threshold
High Side RDS(ON)
VEN(H)
Side
VEN(L)
Input Voltage
Input Voltage
Oscillator Frequency Variation Supply Voltage
Oscillator Frequency Variation Temperature
(VIN 3.6V)
Variation
-0.5 -1.5
Variation
Supply Voltage
Temperature (°C)
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Typical Characteristics
Output Voltage Temperature
(IOUT 900mA; VOUT 1.5V) Output Voltage Error
Line Regulation
(VOUT 1.5V)
0.25 0.15
2.7V
Accuracy
IOUT 1.0A
0.05 -0.05 -0.15 -0.25
-0.2
3.6V
IOUT 0.4A
-0.6
-1.0
Temperature (°C)
Input Voltage
Load Regulation
(VOUT 1.5V; 3.6V)
Load Regulation
(VOUT 3.3V; 5.0V)
VOUT Error
Error
1050
Output Current
IOUT (mA)
Efficiency Input Voltage
(VOUT 1.5V)
Loop Gain Phase Output Capacitor
(VIN 3.6V; IOUT 0.3A; 22µF)
Efficiency
Gain (dB)
Phase
Phase (degrees)
-135
0.4A
Gain
-180 -225 1000
Input Voltage
Frequency (kHz)
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Typical Characteristics
Load Input Current Temperature
(VCC
Non-Switching Temperature
VCC)
Operating Current (µA)
5.5V Input Current (mA)
5.0V
5.5V 5.0V
4.2V 3.6V 2.7V
4.2V
3.6V
2.7V
Temperature (°C)
Temperature (°C)
Switching Waveform
(VIN 3.6V; VOUT 1.5V; IOUT 1.2A)
Transient Response
(VIN 3.6V; VOUT 1.5V; ILOAD 0.25 1.2A)
VOUT 50mV/div
V(LX) 2V/div Inductor Current 500mA/div
500mA/div
500nsec/div
20µs/div
Output Ripple
(VIN 3.6V; VOUT 1.5V; IOUT
Output Ripple
(VIN 3.6V; VOUT 1.5V; IOUT
VOUT 5mV/div BW=20MHz
VOUT 5mV/div BW=20MHz
2V/div
2V/div
500nsec/div
500nsec/div
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Typical Characteristics
Output Ripple
(VIN 5.0V; VOUT 3.3V; IOUT
Output Ripple
(VIN 5.0V; VOUT 3.3V; IOUT
VOUT 5mV/div BW=20MHz
VOUT 5mV/div BW=20MHz
2V/div
2V/div
500nsec/div
500nsec/div
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Functional Block Diagram
2.7V- 5.5V
1.0V
LOGIC
Temp. Sensing Power Good
SGND
PGND
Applications Information
850kHz DC-DC Synchronous Buck Converter Control Loop
AAT1152 peak current mode buck converter. inner, wide bandwidth loop controls peak current output inductor. output inductor current sensed through P-channel MOSFET (high side) also used short-circuit overload protection. fixed slope compensation signal added sensed current maintain stability. 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 error amplifier does have large gain typical most error amplifiers. This eliminates need external compensation components, while still providing sufficient loop gain load regulation. crossover frequency phase margin output capacitor value only.
Soft Start/Enable
Soft start increases inductor current limit point discrete steps when input voltage enable input applied. limits current surge seen input eliminates output voltage overshoot (see Figure When pulled low, enable input forces AAT1152 into low-power, non-switching state. total input current during shutdown less than 1µA.
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
Enable 2V/div
VOUT 1V/div 0.5A/div
200µsec/div
Figure Inrush Limit (VIN 3.6V; VOUT 1.5V; 1A).
Current Limit Over-Temperature Protection
overload conditions, peak input current limited. Figure displays current limit characteristics. load impedance decreases output voltage falls closer zero, more power dissipated internally, raising device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting device from damage. junction over-temperature threshold 140°C with 15°C hysteresis.
Power Signal Source
Separate small signal ground power supply pins isolate internal control circuitry from noise associated with output MOSFET switching. pass filter (shown schematic Figures filters noise associated with power switching.
5.0V 3.3V
VOUT
=3.6V 1.5V
IOUT
Figure Current Limit Characteristics.
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
100k AAT1152-1.0 10µF 100k 0.1µF 2.7µH
Vin+ 3.3V
2.55k 1.25V1A
Sgnd Pgnd
22µF
Murata 10µF 6.3V GRM42-6X 5R106K6.3 MuRata 22µF 6.3V GRM21BR60J226ME39L 0805 Sumida CDRH4D28-2R
Figure 3.3V 1.25V Converter.
1.5V Efficiency IOUT
100k AAT1152-1.5 100k 10µF 0.1µF Sgnd Pgnd 22µF 4.1µH
Vin+ 2.7V-5.5V
1.5V
2.7V
Efficiency
4.2V
3.6V
Murata 10µF 6.3V GRM42-6X5R106K6.3 MuRata 22µF 6.3V GRM21BR60J226ME39L 0805 Sumida CDRH5D 18-4R
1000
Iout (mA)
Figure Lithium-Ion 1.5V Output Converter.
Power Good
AAT1152 features integrated Power Good (POK) comparator open-drain output signal. goes when converter output more below nominal regulation voltage when device shutdown. Connect pull-up resistor from converter input output. Typical resistor pull-up values range from 100k 10k.
Inductor
output inductor selected limit ripple current some predetermined value, typically full load current maximum
input voltage. Manufacturer's specifications list both inductor current rating, which thermal limitation, peak current rating, which determined saturation characteristics. inductor should show appreciable saturation under normal load conditions. During overload short-circuit conditions, average current inductor meet exceed ILIMIT point AAT1152 without affecting converter performance. Some inductors have sufficient peak average current ratings result excessive losses high DCR. Always consider losses associated with effect total converter efficiency when selecting inductor.
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
load ripple maximum input voltage, maximum peak-to-peak ripple current 300mA. inductance value required 3.9µH. VOUT 1.5V 1.5V 11.0A 830kHz 4.2V
Input Capacitor
primary function input capacitor provide impedance loop edges pulsed current drawn AAT1152. ESR/ESL ceramic capacitor ideal this function. minimize stray inductance, capacitor should placed closely possible This keeps high frequency content input current localized, minimizing radiated conducted while facilitating optimum performance AAT1152. Ceramic capacitors ideal this function. size required will vary depending load, output voltage, input voltage source impedance characteristics. typical value around 10µF. input capacitor current varies with input voltage output voltage. equation current input capacitor 1VIN
3.9µH
factor fraction full load selected ripple current maximum input voltage. corresponding inductor current
IRMS
peak-to-peak ripple current which fixed inductor selection above. peak-to-peak current full load current, peak current full load will 115% full load. 4.1µH inductor selected from Sumida CDRH5D18 series 1.95A current rating. full load, inductor loss 57mW, which amounts 3.8% loss efficiency.
IRMS
input capacitor ripple current reaches maximum when times output voltage where approximately half load current. Losses associated with input ceramic capacitor typically minimal issue. Proper placement input capacitor seen reference design layout Figures
Figure AAT1152 Layout Layer.
Figure AAT1152 Layout Bottom Layer.
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
Output Capacitor
Since there external compensation components, output capacitor strong effect loop stability. Larger output capacitance will reduce crossover frequency with greater phase margin. 1.5V design using 4.1µH inductor, 22µF capacitors provide stable output. addition assisting stability, output capacitor limits output ripple provides holdup during large load transitions. output capacitor ripple current given
VOUT (VIN VOUT)
Layout Considerations
Figures display suggested layout AAT1152. most critical aspect layout placement input capacitor proper operation, must placed closely possible AAT1152.
Thermal Calculations
There types losses associated with AAT1152 output switching MOSFET: switching losses conduction losses. Conduction losses associated with RDS(ON) characteristics output switching device. full load, assuming continuous conduction mode (CCM), simplified form total losses
IRMS
ceramic capacitor, dissipation current capacitor concern. Tantalum capacitors with sufficiently meet output voltage ripple requirements also have current rating much greater than that actually seen this application.
PLOSS
(RDSON(H) RDSON(L) (VIN VO))
Adjustable Output
applications requiring output other than fixed outputs available, version programmed externally. Resistors Figure force output regulate higher than should times less than internal resistance pin. Once selected, calculated. 1.25V output with 10.0k, 2.55k.
Once total losses have been determined, junction temperature derived from MSOP-8 package.
0.25 10.0k 2.55k
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
Design Example:
Specifications IOUT IRIPPLE VOUT full load 1.5V 2.7V 4.2V (3.6V nominal) 830kHz
Maximum Input Capacitor Ripple:
IRMS 0.5ARMS,
ESRCOUT IRMS2 0.52A 1.25mW
Inductor Selection:
VOUT 1.5V 1.5V 3.9µH 830kHz 4.2V
Select Sumida Inductor CDRH5D18 4.1µH 2.0mm height.
1.5V 1.5V 280mA 4.1µH 830kHz 4.2V
IOUT
0.14A 1.14A
57mW
Output Capacitor Dissipation:
IRMS VOUT (VIN VOUT) 1.5V (4.2V 1.5V) 82mARMS 4.1µH 830kHz 4.2V
PESR ESRCOUT IRMS2 0.0822A 33µW
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter
AAT1152 Dissipation:
(RDSON(H) RDSON(L) (VIN -VO)) (tsw
(0.14 1.5V 0.145 (3.6V 1.5V)) 3.6V
(20nsec 830kHz 1.0A 0.3mA) 3.6V 0.203W
TJ(MAX) TAMB PLOSS 85°C 150°C/W 0.203W 115°C
Table Surface Mount Inductors
Manufacturer
TaiyoYuden Toko Sumida Sumida MuRata MuRata
Part Number
NPO5DB4R7M A914BYW-3R5M-D52LC CDRH5D28-4R2 CDRH5D18-4R1 LQH55DN4R7M03 LQH66SN4R7M03
Value
4.7µH 3.5µH 4.2µH 4.1µH 4.7µH 4.7µH
Current
1.4A 1.34A 2.2A 1.95A 2.7A 2.2A
0.038 0.073 0.031 0.057 0.041 0.025
Size (mm) Type Shielded Shielded Shielded Shielded Non-Shielded Shielded
Table Surface Mount Capacitors
Manufacturer
MuRata MuRata MuRata MuRata
Part Number
GRM40 106K GRM42-6 106K GRM21BR60J226ME39L GRM21BR60J106ME39L
Value
10µF 10µF 22µF 10µF
Voltage
6.3V 6.3V 6.3V 6.3V
Temp.
Case
0805 1206 0805 0805
1152.2005.01.1.3
AAT1152
850kHz Synchronous Buck DC/DC Converter Ordering Information
Output Voltage 1.0V (Adj. VOUT 1.0V) 1.8V 2.5V 3.3V Package MSOP-8 MSOP-8 MSOP-8 MSOP-8 Marking1 LTXYY MLXYY MMXYY IAXYY Part Number (Tape Reel) AAT1152IKS-1.0-T1 AAT1152IKS-1.8-T1 AAT1152IKS-2.5-T1 AAT1152IKS-3.3-T1
Note: Sample stock held part numbers listed bold. Note assembly date code.
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 0.65 0.30 0.08
0.075 0.075
dimensions millimeters.
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, advise customers 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.
Advanced Analogic Technologies, Inc.
Arques Avenue, Sunnyvale, 94085 Phone (408) 737-4600 (408) 737-4611
1152.2005.01.1.3
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