AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
1171.2009.08.1.3 1
www.analogictech.com
General Description
The AAT1171 SwitchReg™ dynamically controls the oper-
ating voltage of a WCDMA or CDMA power amplifier
inside single-cell, lithium-ion battery-powered systems.
The AAT1171 outputs a voltage between 0.6V and 3.6V,
thereby optimizing the amplifier efficiency at both low
and high transmit levels.
The AAT1171 output voltage is controlled via an analog
signal from the baseband processor. It can deliver
600mA of continuous load current while maintaining a
low 45A of no load quiescent current. The 2MHz switch-
ing frequency minimizes the size of external components
while keeping switching losses low. To further improve
system efficiency, an 85m bypass MOSFET transistor is
also included to allow the PA to be powered directly from
the battery.
The AAT1171 maintains high efficiency thoughout the
entire load range in Light Load (LL) mode, and can be
forced into Pulse Wide Modulation (PWM) mode for low
noise operation or can be synchronized to an external
clock.
The AAT1171 is available in a Pb-free, space-saving
TDFN33-12 or 12-pin wafer-level chip scale package
(WLCSP) and is rated over the -40°C to +85°C tempera-
ture range.
Features
• VIN Range: 2.7V to 5.5V
• Variable Output Voltage: 0.6V to 3.6V
• 600mA Output Current
• DAC Input: 0.2V to 1.2V
• High Output Accuracy: ±3%
• 45A No Load Quiescent Current
• Internal Soft Start Limits Startup Current and Output
Voltage Overshoot
• Synchronizable to External 19.8MHz System Clock
• Over-Temperature and Current Limit Protection
• Integrated 85m Bypass MOSFET
• 2MHz Operation
• PWM/LL Control with Override
• Fast Start-Up:
50s (AAT1171-4, AAT1171-5)
150s (AAT1171-1)
• 100% Duty Cycle Operation
• <30s Output Voltage Response Time
• 3x3mm 12-Pin TDFN or 1.5x2.2mm 12-Pin WLCSP
Package
• Temperature Range: -40°C to +85°C
Applications
• WCDMA or CDMA PA in Cellular Phones, Smartphones,
Feature Phones, etc.
• Express Card
• PCMCIA Data Cards
Typical Application
AAT1171-1/
AAT1171-4
PA
VREF
VCC2
VCC2
VCONT
Baseband
Processor
TX
RX
DAC
0.6V - 3.6V
LX
VOUT
GNDx2
DAC
VIN
4.7μF 4.7μF
2.2μH
EN
MODE/SYNC
BYPASS
VCC
–
CIN COUT
L1
AAT1171-5
PA
VREF
VCC2
VCC2
VCONT
Baseband
Processor
TX
RX
DAC
0.6V - 3.6V
LX
VOUT
GNDx2
DAC
VIN
4.7μF 10μF
4.7μH
EN
MODE/SYNC
BYPASS
VCC
–
CIN COUT
L1
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
2 1171.2009.08.1.3
www.analogictech.com
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
2 1171.2009.08.1.3
www.analogictech.com
Pin Descriptions
Pin #
Symbol Function
TDFN33-12 WLCSP-12
1 N/A N/C Not connected.
2, 3 5, 9 VOUT
Feedback input pin. This pin is connected to the converter output. It is used to
complete the control loop, regulating the output voltage to the desired value.
When in bypass mode, a low resistance MOSFET is connected between this pin
and VIN.
4 7 VCC Bias supply. Supply power for the internal circuitry. Connect to input power via
low pass fi lter with decoupling to AGND.
5 6 AGND Analog ground. Connect the return of all small signal components to this pin.
6 1 DAC Control voltage input from a DAC. Input voltage between 0.2V and 1.2V to con-
trol output voltage of the converter. Force pin to 1.3V for bypass switch enable.
7 2 EN Enable DC/DC converter, active high.
8 3 BYPASS Enable control to bypass the DC/DC converter when PA transmitting at full
power from low battery voltage. Active high.
9 4 MODE/SYNC
This pin is used to program the device between PWM and LL mode:
HIGH - PWM Mode Only
LOW - LL Mode: PWM operation for loads above 100mA and variable switching
frequency for loads below 100mA. Connecting the SYNC pin to the system clock
(19.8MHz) will override the internal clock and force the switching frequency to
the external clock frequency divided by 10.
10 12 VIN Input supply voltage for the converter. Must be closely decoupled.
11 8, 11 PGND Main power ground. Connect to the output and input capacitor return.
12 10 LX Switching node. Connect the inductor to this pin. It is connected internally to
the drain of both low- and high-side MOSFETs.
EP N/A Exposed paddle (bottom). Connect to ground directly beneath the package.
Pin Configuration
TDFN33-12 WLCSP-5
(Top View) (Top View)
N/C
VOUT
VOUT
1
VCC
A
GND
DAC
LX
PGND
VIN
MODE/SYNC
BYPASS
EN
2
3
4
5
6
12
11
10
9
8
7
121110
789
654
123
VIN
VCC
AGND
DAC
5: VOUT
2: EN
11: PGND
8: PGND
LX
VOUT
MODE/SYNC
BYPASS
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
1171.2009.08.1.3 3
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Absolute Maximum Ratings1
Symbol Description Value Units
VCC, VIN Input Voltage and Bias Power to GND 6.0 V
VLX LX to GND -0.3 to VIN + 0.3 V
VOUT VOUT to GND -0.3 to VIN + 0.3 V
VNEN, DAC, BYPASS, MODE/SYNC to GND -0.3 to 6.0 V
TJOperating Junction Temperature Range -40 to 150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C
Thermal Information2
Symbol Description Value Units
PDMaximum Power Dissipation, TA = 25°C TDFN33-122, 3 2.0 W
WLCSP-122, 4 0.88
JA Thermal Resistance, TA = 25°C TDFN33-12 50 °C/W
WLCSP-12 114
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 FR4 board; for the WLCSP package, use the NSMD (none-solder mask defined) pad style for tighter control on the copper etch process.
3. Derate 20mW/°C above 25°C ambient.
4. Derate 8.8mW/°C above 25°C ambient.
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
4 1171.2009.08.1.3
www.analogictech.com
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
4 1171.2009.08.1.3
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Electrical Characteristics1
TA = -40°C to +85°C, unless otherwise noted. VIN = VCC = 3.6V; typical values are TA = 25°C.
Symbol Description Conditions Min Typ Max Units
VIN Input Voltage 2.7 5.5 V
VUVLO
UVLO Threshold VIN Rising 2.6 V
UVLO Hysteresis 200 mV
VOUT VOUT Programmable Range 0.6 3.6 V
VDACIN Input Voltage Range from DAC 0.2 1.2 V
IQQuiescent Current No Load, Light Load 45 70 A
No Load, PWM, VCC Bias Current 420
ISHDN Shutdown Current EN = AGND = PGND 1.0 A
ILIM P-Channel Current Limit TA = 25°C 1.2 1.6 A
RDS(ON)H High Side Switch On Resistance 230 m
RDS(ON)L Low Side Switch On Resistance 230 m
RDS(ON)BP Bypass Switch Resistance VDAC = 1.3V or BYPASS = VIN 85 m
ILXLEAK LX Leakage Current VCC = 5.5V, VLX = 0 to VCC 1A
VOUT/
VOUT
Load Regulation ILOAD = 0 to 500mA 0.5 %
VOUT/
VOUT/VIN
Line Regulation 0.2 %/V
ROUT Feedback Impedance 170 k
VOUT Output Voltage Accuracy VDAC = 0.6V, ILOAD = 0 1.746 1.8 1.854 V
FOSC Oscillator Frequency 2.0 MHz
TSD Over-Temperature Shutdown Threshold 140 °C
THYS Over-Temperature Shutdown Hysteresis 15 °C
ILL Light Load Load Current Threshold 100 mA
tVOUTS Output Voltage Settling Time VOUT = 0.6V to VOUT(MAX), MODE/SYNC = VIN 30 s
PWM/Light Load/EN
VEN(L) Enable Threshold Low 0.6 V
VEN(H) Enable Threshold High 1.4 V
IEN Input Low Current VCC = 5.5V -1.0 1.0 A
tEN Turn-On Enable Response Time
AAT1171-1: EN = Low to High, MODE/SYNC
= High, VDAC = 1.2V 150
s
AAT1171-4/AAT1171-5: EN = Low to High,
MODE/SYNC = High, VDAC = 1.2V 50
SYNC
FSYNC Synchronization Frequency Sync to 19.8MHz219.8 MHz
VSYNC(H) SYNC High Level Threshold 1.6 V
VSYNC(L) SYNC Low Level Threshold 0.6
ISYNC SYNC Low Current VSYNC = GND or VCC -1.0 1.0 A
DAC Input
Gain Output Voltage/DAC Voltage33 V/V
1. The AAT1171 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
2. Please contact Sales for other synchronization frequencies.
3. Please contact Sales for other output voltage/DAC voltage gains.
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
1171.2009.08.1.3 5
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
1171.2009.08.1.3 5
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Typical Characteristics
Efficiency vs. Output Current
(LL Mode; VOUT = 3.3V)
Output Current (mA)
Efficiency (%)
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 5.0V
VIN = 4.2V
VIN = 3.9V
Load Regulation
(LL Mode; VOUT = 3.3V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1 1 10 100 1000
VIN = 5.0V
VIN = 4.2V
VIN = 3.6V
Efficiency vs. Output Current
(PWM Mode; VOUT = 3.3V)
Output Current (mA)
Efficiency (%)
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.6V
VIN = 5.0V
VIN = 4.2V
Load Regulation
(PWM Mode; VOUT = 3.3V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1 1 10 100 1000
VIN = 5.0V
VIN = 4.2V
VIN = 3.6V
Efficiency vs. Output Current
(LL Mode; VOUT = 2.5V)
Output Current (mA)
Efficiency (%)
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.0V
VIN = 4.2V
VIN = 5.0V
Load Regulation
(LL Mode; VOUT = 2.5V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1 1 10 100 1000
VIN = 5.0V
VIN = 4.2V
VIN = 3.0V
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
6 1171.2009.08.1.3
www.analogictech.com
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
6 1171.2009.08.1.3
www.analogictech.com
Typical Characteristics
Efficiency vs. Output Current
(PWM Mode; VOUT = 2.5V)
Output Current (mA)
Efficiency (%)
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.0V
VIN = 4.2V
VIN = 5.0V
Load Regulation
(PWM Mode; VOUT = 2.5V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1 1 10 100 1000
VIN = 5.0V
VIN = 4.2V
VIN = 3.0V
Efficiency vs. Output Current
(LL Mode; VOUT = 1.8V)
Output Current (mA)
Efficiency (%)
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
Load Regulation
(LL Mode; VOUT = 1.8V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0 1 10 100 1000
VIN = 3.6V
VIN = 2.7V
VIN = 4.2V
Efficiency vs. Output Current
(PWM Mode; VOUT = 1.8V)
Output Current (mA)
Efficiency (%)
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000.
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
Load Regulation
(PWM Mode; VOUT = 1.8V)
Output Current (mA)
Output Voltage Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1 1 10 100 1000
VIN = 3.6V
VIN = 4.2V
VIN = 2.7V
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
1171.2009.08.1.3 7
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Typical Characteristics
Output Voltage vs. Supply Voltage
(LL Mode; VOUT = 1.5V)
Supply Voltage (V)
Output Voltage (V)
1.494
1.498
1.502
1.506
1.510
1.514
2.7 2.9 3.1 3.3 3..5 3.7 3..9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
IOUT = 50mA
IOUT = 300mA
IOUT = 600mA
Output Voltage vs. Supply Voltage
(PWM Mode; VOUT = 1.5V)
Supply Voltage (V)
Output Voltage (V)
1.494
1.498
1.502
1.506
1.510
1.514
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
IOUT = 50mA
IOUT = 300mA
IOUT = 600mA
Output Voltage vs. Temperature
(VIN = 3.6V; VOUT = 1.8V; VDAC = 0.6V; RL = 10)
Temperature (°
°
C)
Output Voltage Error (%)
-1.5
-1.0
-0.5
0.0
0.5
1.0
-40 -15 10 35 60 85
Bypass Mode Dropout Voltage
vs. Load Current
Load Current (mA)
Dropout Voltage (V)
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.1 1 10 100 1000
Supply Current vs. Supply Voltage
(No Load; LL Mode)
Supply Voltage (V)
Supply Current (µA)
30
35
40
45
50
55
60
65
70
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VOUT = 1.8V
VOUT = 0.6V
Supply Current vs. Supply Voltage
(No Load; PWM Mode)
Supply Voltage (V)
Supply Current (mA)
3.0
3.5
2.0
2.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VOUT = 1.8V
VOUT = 0.6V
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
8 1171.2009.08.1.3
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Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
2.7 3.1 3.5 3.9 4.5 4.9 5.52.9 3.3 3.7 4.1 4.3 4.7 5.1 5.3
0
50
100
150
200
250
300
350
400
TJ = 120°CTJ = 85°C
TJ = 25°C
Bypass RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON) (mΩ
Ω
)
0
20
40
60
80
100
120
140
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
TJ = 25°C
TJ = 85°C
TJ = 120°C
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V; RL = 10)
Temperature (°
°
C)
Switching Frequency (MHz)
1.90
1.92
1.94
1.96
1.98
2.00
2.02
2.04
2.06
-40.0 -20.0 0.0 20.0 40.0 60.0 80.0
LL
PWM
Output Voltage vs. DAC Voltage
(VIN = 4.2V; LL Mode)
DAC Voltage (V)
Output Voltage (V)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.2 0.4 0.6 0.8 1.0 1.2 1.4
25°C
85°C
-40°C
Heavy Load Switching Waveform
(VIN = 3.6V; VOUT = 1.8V; RL = 3Ω; COUT = 4.7µF; L = 2.2µH)
Time (200ns/div)
VOUT
(AC coupled)
20mV/div
IL
200mA/div
VLX
2V/div
0
0
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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Typical Characteristics
Light Load Switching Waveform
(PWM Mode; VIN = 4.2V; VOUT = 0.6V; RL = 10Ω;
COUT = 4.7µF; L = 2.2µH)
Time (200ns/div)
VOUT
(AC coupled)
20mV/div
IL
100mA/div
VLX
2V/div
0
0
Light Load Switching Waveform
(LL Mode; VIN = 4.2V; VOUT = 0.6V; RL = 10Ω;
COUT = 4.7µF; L = 2.2µH)
Time (1µs/div)
VOUT
(AC coupled)
20mV/div
IL
200mA/div
VLX
2V/div
0
0
DAC Transient Response in PWM Mode
(VIN = 3.6V; RL = 10Ω; COUT = 4.7µF; L = 2.2µH)
Time (25µs/div)
VOUT
1V/div
VDAC
0.5V/div
0
0
3.3V
0.6V
1.2V
0.2V
DAC Transient Response in LL Mode
(VIN = 3.6V; RL = 10Ω; COUT = 4.7µF; L = 2.2µH)
Time (25µs/div)
VOUT
1V/div
VDAC
0.5V/div
0
0
3.3V
0.6V
1.2V
0.2V
Bypass Transient Response
(PWM Mode; VIN = 3.6V; RL = 10Ω; COUT = 4.7µF; L = 2.2µH)
Time (25µs/div)
VOUT
1V/div
VBYP
1V/div
0
0
3.5V
0.6V
Bypass Transient Response
(LL Mode; VIN = 3.6V; RL = 10Ω; COUT = 4.7µF; L = 2.2µH)
Time (25µs/div)
VOUT
1V/div
VBYP
1V/div
0
0
3.5V
0.6V
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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Typical Characteristics
DAC to Bypass Transient Response
(LL Mode; VIN = 4.2V; RL = 10Ω; COUT = 4.7µF; L = 2.2µH)
Time (25µs/div)
VOUT
1V/div
VDAC
0.5V/div
0
0
0.6V
4.2V
1.3V
0.2V
Enable Soft Start
(VIN = 3.6V; VOUT = 1.8V; RL = 3.9Ω;
COUT = 4.7µF; L = 2.2µH)
Time (20µs/div)
VOUT
1V/div
Enable
2V/div
IIN
200mA/div
0V
0V
0A
1.8V
Load Transient Response
(VIN = 4.2V; VOUT = 3.3V; COUT = 4.7µF; L = 2.2µH)
Time (20µs/div)
VOUT
(AC coupled)
20mV/div
IOUT
200mA/div
525mA
250mA
3.51V
3.26V
Load Transient Response
(VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; L = 2.2µH)
Time (20µs/div)
VOUT
(AC coupled)
20mV/div
IOUT
100mA/div
200mA
500mA
1.914V
1.798V
Line Transient Response
(VOUT = 1.5V; RL = 10Ω
Ω
; COUT = 4.7µF; L = 2.2µH)
Time (50µs/div)
VOUT
(AC coupled)
50mV/div
VIN
0.5V/div
3.6V
3.0V
1.56V
1.44V
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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Functional Description
The AAT1171 is a 600mA 2MHz peak current mode syn-
chronous step-down (buck) converter designed to oper-
ate from a single-cell lithium-ion battery with a 2.7V to
4.2V input range. The output voltage is dynamically pro-
grammed by the DAC input voltage.
To maximize converter efficiency over all load conditions,
the converter automatically transitions to a variable fre-
quency light load (LL) mode when the load is less than
100mA. When combined with the very low quiescent cur-
rent, the LL mode maintains a high efficiency over the
complete load range. For noise sensitive applications,
the converter can be forced into a fixed frequency PWM
mode. Provisions are also made for synchronization of
the converter to an external system clock.
The synchronous buck converter power output devices
are sized at 230m for a 600mA full load output current.
In addition to the converter output, an additional low
resistance bypass MOSFET (85m) can be connected
between the battery input and the converter output (VIN
to VOUT), bypassing the converter and output inductor to
improve headroom and extend the WCDMA PA full power
range. This reduces the battery voltage necessary for a
WCDMA RF power amplifier to meet linearity require-
ments, thus extending operating time. In dual mode
systems, the bypass mode may also be used when the
WCDMA RF power amplifier is in GSM mode. Bypass
mode is activated by setting the bypass input high or by
forcing the baseband DAC output voltage to 1.3V.
The AAT1171 requires only three external components
for operation (CIN, COUT
, LX). The high 2MHz switching
frequency reduces the inductor size required to 2.2H
for the AAT1171-1/AAT1171-4 and 4.7H for the
AAT1171-5. This reduces the DC resistance and improves
the converter efficiency while minimizing the inductor
Functional Block Diagram
Logic
DH
DL
Comp
Error
Amp
VOUT VCC VIN
L
X
AGND PGND
DAC
EN
BYPASS
MODE/SYNC
MODE/SYNC
Interface
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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footprint and height. The output voltage of the converter
is regulated to within 0.5% and will settle in less than
30s (according to WCDMA specifications) in response to
any step change in the DAC input.
Under-voltage lockout, internal compensation, soft-start,
over-current, and over-temperature protection are also
included.
DAC Output Voltage Control
The output voltage is programmed by way of the DAC
input voltage. The DAC to output gain for the AAT1171
is 3.
VOUT = 3 · VDAC
The DAC input voltage range is 0.2V to 1.2V, which cor-
responds to an output voltage range of 0.6V to 3.6V (see
Figure 1). For a 1.3V DAC level, the bypass switch is
activated and the output voltage level is equivalent to
the input voltage minus the bypass MOSFET (RDS(ON)(bp))
drop.
Bypass Mode
In bypass mode, the AAT1171 bypasses the output
inductor, connecting the input directly to the output
through a low RDS(ON) 85m MOSFET. Bypass mode is
initiated by applying 1.3V to the DAC input or by apply-
ing a logic high to the bypass input. When not activated,
a logic level low must be applied to the bypass input pin.
The bypass MOSFET current is limited to 600mA.
LL/PWM Control
Two control modes are available with the AAT1171: LL
mode and PWM mode. PWM mode maintains a fixed
switching frequency regardless of load. The fixed switch-
ing frequency gives the advantage of lower output ripple
and simplified output and input noise filtering. PWM
mode also provides a faster output voltage response to
changes in the DAC voltage.
In LL mode, the converter transitions to a variable
switching frequency as the load decreases below 100mA.
Above 100mA, where switching losses no longer domi-
nate, the switching frequency is fixed. The LL mode’s
effect on the DAC to output voltage response time is
most notable when transitioning from a high output volt-
age to a low voltage. When the converter is in PWM
mode, the inductor current can be reversed and the out-
put voltage actively discharged by the synchronous
MOSFET. While in LL mode, the output voltage is dis-
charged by the load only, resulting in a slower response
to a DAC transition from a high to a low voltage.
For PWM mode, apply a logic level high to the MODE/
SYNC pin; for LL mode, apply a logic level low to the
MODE/SYNC pin.
Soft Start/Enable
The AAT1171 soft-start control prevents output voltage
overshoot and limits inrush current when either the input
power or the enable input is applied. When pulled low,
the enable input forces the converter into a low-power,
non-switching state with less than 1A bias current.
1V
2V
3V
4V
3.6V
1V 1.2V
DAC Output
Output to PA
0.6V
0.2V
V
IN
1.3V
BYPASS MODE
Figure 1: VOUT vs. VDAC.
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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Low Dropout Operation
For conditions where the input voltage drops to the out-
put voltage level, the converter duty cycle increases to
100%. As 100% duty cycle is approached, the minimum
off-time initially forces the high-side on-time to exceed
the 2MHz clock period, reducing the converter switching
frequency. Once the input drops to the level where the
output can no longer be regulated, the high-side P-channel
MOSFET is enabled continuously for 100% duty cycle. The
output voltage then tracks the input voltage minus the IR
drop of the high side P-channel MOSFET RDS(ON).
UVLO Shutdown
Under-voltage lockout (UVLO) circuitry monitors the input
voltage and disables the converter when the input voltage
drops to 2.4V, guaranteeing sufficient operating input
voltage to maintain output voltage regulation and control.
For a rising input voltage, the UVLO circuitry enables the
converter 200mV above the shutdown level at 2.6V.
Current Limit and
Short-Circuit Protection
The high-side P-channel MOSFET current limit compara-
tor limits the peak inductor current to 1.6A. In PWM
mode, the synchronous MOSFET current limit compara-
tor limits the peak negative inductor current, and output
capacitor discharge current is limited to 1A. In bypass
mode, the bypass MOSFET current is limited to 600mA.
In the event of an overload or short-circuit condition, the
current limit protects the load and the AAT1171 power
devices. Upon removal of the short-circuit or fault condi-
tion, the AAT1171 output automatically recovers to the
regulated level.
Thermal Overload Protection
The maximum junction temperature is limited by the
AAT1171 over-temperature shutdown protection circuit-
ry. Both the step-down converter and the bypass
MOSFET are disabled when the junction temperature
reaches 140°C. Normal operation resumes once the
junction temperature drops to 125°C.
External Synchronization
The AAT1171 switching frequency can be synchronized to
an external square wave clock via the MODE/SYNC input.
The external clock frequency range and logic levels for
which the AAT1171 will remain synchronized are listed in
the Electrical Characteristics table of this datasheet.
Applications Information
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. Because the required
slope compensation varies with output voltage, the
AAT1171 varies the slope compensation to match the
output voltage. This allows the use of a single inductor
value for all output voltage levels. The inductor value is
2.2H for the AAT1171-1/AAT1171-4 and 4.7H for the
AAT1171-5.
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 satura-
tion characteristics.
The inductor should not show any appreciable saturation
under normal load conditions. The inductor ripple cur-
rent varies with both the input voltage and the output
voltage and peaks at the maximum input voltage with
the output at one half of the input voltage. For the typi-
cal AAT1171, this corresponds to a 4.2V input voltage
and a 2.1V output voltage. With the suggested 2.2H
inductor, this corresponds to 239mA peak-to-peak ripple
current. For a 600mA DC load current, the peak inductor
current would be 718mA. In order to prevent saturation
under normal load conditions, the peak inductor current
should be less than the inductor saturation current.
V
IN(MAX)
8 ⋅ L ⋅ F
S
4.2V
8 ⋅ 2.2µH ⋅ 2MHz
I
PK(MAX)
= I
O
+
= 0.6A +
= 0.6A + 0.12A
= 0.72A
Some inductors may meet peak and average current
requirements 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. The inductor losses can be esti-
mated by using the full load output current. The output
inductor losses can then be calculated to estimate their
effect on overall device efficiency.
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
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P
O
P
O
+ PL
3.4 ⋅ 0.6A
3.4V ⋅ 0.6A + 50mW
η = = = 97%
PL = I
O2
⋅ DCR = 0.6A
2
⋅ 0.14Ω = 50mW
The 2.2H inductor selected for the AAT1171 evaluation
board has a 140m DCR and a 0.91A DC current rating.
At 600mA load current, the inductor loss is 50mW which
gives 2.4% loss in efficiency for a 600mA 3.4V output
voltage with an inductor that measures 3.2x3.2x1.2mm.
Output Capacitor Selection
The AAT1171-1/AAT1171-4 are designed for use with
4.7F 10V X5R ceramic output capacitors, while the
AAT1171-5 is designed for use with 10F 10V X5R
ceramic output capacitors. Although a larger output
capacitor provides improved response to large load tran-
sients, it also limits the output voltage rise and fall time
in response to the DAC input. For stable operation, with
sufficient phase and gain margin, the internal voltage
loop compensation limits the minimum output capacitor
value to 4.7F. Increased output capacitance will reduce
the crossover frequency with greater phase margin.
The output voltage droop due to load transients is dom-
inated by the output capacitor. During a step increase in
load current, the output capacitor supplies the load cur-
rent while the control loop responds. Within two or three
switching cycles, the inductor current increases to match
the load current demand. The relationship of the output
voltage droop during the three switching cycles to the
output capacitance can be estimated by:
COUT =
3 · ∆ILOAD
VDROOP · FS
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion establishes a limit on the minimum output capacitor
value necessary to meet a given output voltage droop
requirement (VDROOP) for a given load transient.
The maximum output capacitor RMS ripple current is:
1
23
VOUT · (VIN(MAX) - VOUT)
RMS(MAX)
IL · FS · VIN(MAX)
=·
·
Dissipation due to the RMS current in the ceramic output
capacitor ESR is typically minimal, resulting in less than
a few degrees rise in hot-spot temperature.
Input Capacitor Selection
A 10V X5R or X7R ceramic capacitor is suggested for the
input capacitor with typical values ranging from 4.7F to
10F. To estimate the required input capacitance size,
determine the acceptable input ripple level (VPP) and solve
for C, as shown below. The calculated value varies with
input voltage and is a maximum when VIN is double the
output voltage. Always examine the ceramic capacitor DC
voltage coefficient characteristics when selecting the
proper value. For example, due to the voltage coefficient
of a 10F 6.3V X5R ceramic capacitor, with an applied
voltage of 5V DC the capacitance decreases to 6F.
⎛⎞
· 1 -
⎝⎠
VO
VIN
CIN =
VO
VIN
⎛⎞
- ESR · FS
⎝⎠
VPP
IO
⎛⎞
· 1 - =
⎝⎠
VO
VIN
VO
VIN
1
4
CIN(MIN) = 1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
The maximum input capacitor RMS current is:
⎛⎞
IRMS = IO · · 1 -
⎝⎠
VO
VIN
VO
VIN
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current.
⎛⎞
· 1 - = D · (1 - D) = 0.52 =
⎝⎠
VO
VIN
VO
VIN
1
2
for VIN = 2 · VO
IO
RMS(MAX)
I2
=
The term
⎛⎞
· 1 -
⎝⎠
VO
VIN
VO
VIN appears in both the input voltage
ripple and input capacitor RMS current equations and is
a maximum when VIN is twice Vo; therefore, the input
voltage ripple and the input capacitor RMS current ripple
are a maximum at 50% duty cycle.
AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
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The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1171. Low
ESR/ESL X7R and X5R ceramic capacitors are ideal for
this function. To minimize stray inductance, the capaci-
tor should be placed as closely as possible to the IC. This
keeps the high frequency content of the input current
localized, minimizing EMI and input voltage ripple.
The proper placement of the input capacitor (C1) can be
seen in the evaluation board layout in Figure 4.
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the eval-
uation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients with errors in loop phase and gain
measurements.
Since the inductance of a short PCB trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most applications do not
exhibit this problem.
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic capacitor (C3 of Figure 5) should be
placed in parallel with the low ESR, ESL bypass ceramic
capacitor. This dampens the high Q network and stabi-
lizes the system.
DAC Programming Gain
The output voltage is dynamically controlled by the DAC
input voltage. The DAC to output gain is fixed at 3. The
typical response time for a 0.2V to 1.2V pulsed signal on
the DAC input is less than 30s. The DAC gain can be
reduced by an external resistive divider at the DAC
input, as shown in the evaluation board schematic in
Figures 2 and 3. For a DAC to output gain of 2 and R2
at 10k, R1 is 4.99k.
(3- G
DAC
)R2
G
DAC
(3 - 2)10kΩ
2
R1 = = = 4.99kΩ
Thermal Calculations
There are three types of losses associated with the
AAT1171 step-down converter: switching losses, con-
duction losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteristics of
the power MOSFET devices. Switching losses are domi-
nated by the gate charge of the power MOSFET devices.
The AAT1171 main and synchronous power MOSFETs are
sized to have similar RDS(ON) values that track with the
input voltage. At full load, assuming continuous conduc-
tion mode (CCM), a simplified form of the step-down
converter losses is given by:
PTOTAL = IO
2 · RDS(ON) + (tSW · FS · IO + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load switching loss-
es, which are dominated by the gate charge losses.
For the condition where the buck converter is at 100%
duty cycle dropout, the total device dissipation reduces
to:
PTOTAL = IO
2 · RDS(ON) + IQ · VIN
In bypass mode, the bypass MOSFET RDS(ON)(bp) is used to
determine the losses. The power MOSFET RDS(ON) increas-
es with decreasing input voltage and the associated
losses are a maximum at the minimum input voltage
(2.7V).
PTOTAL = IO
2 · RDS(ON)(bp) + IQ · VIN
Since the RDS(ON), quiescent current, and switching losses
all vary with input voltage, the total losses should be
investigated over the complete input voltage range.
After calculating the total losses, the maximum junction
temperature can be derived from the JA for the TDFN33-
12 package which is typically 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
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2.2μH
L1
4.7μF
C2
BYPASS
4.7μF
C1
1 2 3321123
ENABLE
VOUT
DAC
VOUT
2
N/C
1
PGND
11
EN 7
BYPASS 8
VIN 10
VOUT
3
LX 12
MODE/SYNC 9
DAC
6
AGND
5
VCC
4
AAT1171-1/AAT1171-4
U1
VIN
GND
SYNC
R1 R2
GND
PWMLL
On OffOnOff
Figure 2: AAT1171-1/AAT1171-4 Evaluation Board Schematic.
4.7μH
L1
10μF
C2
BYPASS
4.7μF
C1
1 2 3321123
ENABLE
VOUT
DAC
VOUT
2
N/C
1
PGND
11
EN 7
BYPASS 8
VIN 10
VOUT
3
LX 12
MODE/SYNC 9
DAC
6
AGND
5
VCC
4
AAT1171-5
U2
V
IN
GND
SYNC
R1 R2
GND
PWMLL
On OffOnOff
Figure 3: AAT1171-5 Evaluation Board Schematic.
AAT1171
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WLCSP Package Light Sensitivity
The electrical performance of the WLCSP package can be
adversely affected by exposing the device to certain light
sources such as direct sunlight or a halogen lamp whose
wavelengths are red and infra-reds. However, fluores-
cent lighting has very little effect on the electrical per-
formance of the WLCSP package.
Layout
The suggested PCB layout for the AAT1171 is shown in
Figures 4 and 5. The following guidelines should be used
to ensure a proper layout.
1. The input capacitor (C1) should connect as closely
as possible to VIN (Pin 10) and PGND (Pin 11).
2. C2 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin should be as
short as possible.
3. The PCB trace connected to VOUT (Pins 2 and 3) is
tied to the bypass path, as well as the feedback path
for the control loop. In bypass mode, the full load
current is delivered directly from the battery input;
therefore, this trace should be sufficient to handle
current up to the bypass current limit level.
4. The resistance of the trace from the load return to
PGND (Pin 11) should be kept to a minimum. This
minimizes any error in DC regulation due to differ-
ences in the potential of the internal signal ground
and the power ground.
5. For good thermal coupling, PCB vias are required
from the pad for the TDFN exposed paddle to the
ground plane. The via diameter should be 0.3mm to
0.33mm and positioned on a 1.2mm grid.
Figure 4: AAT1171 Evaluation Board Figure 5: AAT1171 Evaluation Board
Top Side Layout. Bottom Side Layout.
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PA Step-Down Converter Design Example
Specifications
VO(BUCK) 0.6V to 3.4V with RL =10
VIN 2.7V to 4.2V (3.6V nominal)
FS 2.0MHz
TAMB 85°C
Output Inductor
L1 = 2.2H
For Copper Electronics SD3112, 2.2H, DCR = 140m.
V
O
V
O
2.1
V
2.1V
ΔI
L1(MAX)
= ⋅ 1 - = ⋅ 1 - = 239m
A
L ⋅ F
S
V
IN
2.2µH ⋅ 2.0MHz
4.2V
⎛
⎝⎞
⎠
⎛
⎝⎞
⎠
The maximum inductor ripple current occurs at 50% duty cycle at the maximum input voltage.
I
PKL1
= I
O
+ ΔI
L1(MAX)
= 0.6A + 0.118A = 0.718
A
2
P
L1
= I
O
2
⋅ DCR = 0.6A
2
⋅ 140mΩ = 50mW
Output Capacitor
Specify that VDROOP = 0.2V for a 600mA load pulse.
1
23
1 3.4V · (4.2V - 3.4V)
4.7µH · 2.0MHz · 4.2V
23
RMS
IL1 · FS · VIN(MAX)
= ·
·
3 · ΔILOAD
VDROOP · FS
3 · 0.6A
0.2V · 2.0MHz
COUT = = = 4.5µF
· = 69mArms
·
(VO) · (VIN(MAX) - VO)=
PESR = ESR · IRMS2 = 5mΩ · (69mA)2 = 24µW
Input Capacitor
Specify a maximum input voltage ripple of VPP = 25mV.
CIN(MIN) = = = 3.4µF
1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
1
⎛⎞
- 5mΩ · 4 · 2.0MHz
⎝⎠
25mV
0.6A
IO
RMS
I
P = ESR · IRMS
2 = 5mΩ · (0.3A)2 = 0.45mW
2
= = 0.3Arms
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AAT1171 Losses
PTOTAL
= 0.62 · 0.29Ω + (5ns · 2.0MHz · 0.6A + 60µA) · 4.2V = 104m
= IO
2 · RDS(ON) + (tsw · FS · IO + IQ) · VIN
TJ(MAX) = PTOTAL · ΘJA + TAMB = 104mW · 50°C/W = 5.2°C + 70°C = 75.2°C
AAT1171 Dropout Losses
PTOTAL
= 0.62 · 310mΩ + 100µA · 3.5V = 112mW
= IO
2 · RDS(ON)(HS) + IQ · VIN
TJ(MAX) = PTOTAL · ΘJA + TAMB = 112mW · 50°C/W = 5.6°C + 70°C = 75.6°C
AAT1171
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Manufacturer Value Device Voltage Case Size Part Number
AVX
www.avxcorp.com 10F Output Capacitor 10V 0805 0805ZD106KAT
Murata
www.murata.com
4.7FOutput or Input Capacitor 10V 0805 GRM21BR61A475KA73L
Input Capacitor 6.3V 0603 GRM188R60J475KE19D
10F Output Capacitor 10V 0805 GRM21BR61A106K
TDK
www.tdk.com
4.7FOutput or Input Capacitor 10V 0805 C2012X5R1A475K
Input Capacitor 6.3V 0603 C1608X5ROJ475K
10F Output Capacitor 10V 0805 C2012X5R1A106K
Taiyo Yuden
www.t-yuden.com 4.7FOutput or Input Capacitor 10V 0805 LMK212BJ475MG
Input Capacitor 6.3V 0603 JMK107BJ475MA
Manufacturer Value ISAT I
RMS DCR Case Size
(mm) Part Number
Cooper Electronics
www.cooperet.com
2.2H 1.12A 0.91A 140mΩ3.1x3.1x1.2 SD3118-2R2
4.7H 0.8A 0.74A 246m3.1x3.1x1.2 SD3112-4R7-R
Sumida
www.sumida.com
2.2H 1.1A 1.3A 96mΩ3.2x3.2x1.2 CDRH2D11/HP
4.7H 0.75A 0.85A 238m3.2x3.2x1.2 CDRH2D11/HP
ABCO Electronics
www.abco.co.kr
2.2H 0.52A 200mΩ 2.0x2.0x1.0 LPF2010-2R2M
2.2H 0.55A 110mΩ 2.0x2.0x1.4 LPF2010-2R2M
Table 1: Suggested Component Selection.
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Ordering Information
Package Marking1Part Number (Tape and Reel)2
TDFN33-12 RXXYY AAT1171IWP-1-T13
TDFN33-12 XCXYY AAT1171IWP-4-T13
TDFN33-12 XDXYY AAT1171IWP-5-T13
WLCSP-12 UGYW4AAT1171IUP-1-T13
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/aboutus/quality.php.
Package Information5
TDFN33-12
Top View Bottom View
Detail "A"
Side View
3.00
±
0.05
Index Area Detail "A"
1.70
±
0.05
3.00
±
0.05
0.05
±
0.05
0.23
±
0.05
0.75
±
0.05
2.40
±
0.05
0.43
±
0.05
0.45
±
0.050.23
±
0.05
0.1 REF
Pin 1 Indicator
(optional)
C0.3
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. Available exclusively outside of the United States and its territories.
4. YW = data code (year, week) for WLCSP-12 package.
5. 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.
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AAT1171
600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass SwitchSwitchRegTM
PRODUCT DATASHEET
22 1171.2009.08.1.3
www.analogictech.com
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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 specifi cations 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 fi tness 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. Specifi c 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.
WLCSP-12
1.000
1.535
±
0.035
1.500
0.250
0.500 BSC
0.300
0.300
0.200
Line 1:
Part Code
Line 2:
Year Code and
Bi-Week Code
(laser marking)
ø 0.2 (Ref.)
Pin 1 indication
0.600
±
0.075
0.380
0.25 +
0.03
- 0.04
2.235 +
0.035
- 0.015
0.300
0.100
Top View
End View Side View
Bottom View
All dimensions in millimeters.