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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Features
* * * * VIN Range: 2.7V to 5.5V Low Noise Light Load Mode Low Ripple PWM Mode Output Current: Channel 1: 600mA Channel 2: 600mA 96% Efficient Step-Down Converter Low No Load Quiescent Current 70A Total for Both Converters Integrated Power Switches 100% Duty Cycle 1.7MHz Switching Frequency Optional Fixed Frequency or External SYNC Logic Selectable 180 Phase Shift Between the Two Converters Current Limit Protection Automatic Soft-Start Over-Temperature Protection QFN33-16 Package -40C to +85C Temperature Range
General Description
The AAT2713 is a high efficiency dual synchronous stepdown converter for applications where power efficiency, thermal performance and solution size are critical. Input voltage ranges from 2.7V to 5.5V, making it ideal for systems powered by single-cell lithium-ion/polymer batteries. The AAT2713 incorporates a unique low noise architecture which reduces ripple and spectral noise. Each converter is capable of 600mA output current and has its own enable pin. Efficiency of the converters is optimized over full load range. Total no load quiescent current is 70A, allowing high efficiency even under light load conditions. The integrated power switches are controlled by pulse width modulation (PWM) with a 1.7MHz typical switching frequency at full load, which minimizes the size of external components. Fixed frequency, low noise operation can be forced by a logic signal on the MODE pin. Furthermore, an external clock can be used to synchronize the switching frequency of both converters. A phase shift pin (PS) is available to operate the two converters 180 out of phase at heavy load to achieve low input ripple. The AAT2713 is available in a Pb-free, thermally enhanced 16-pin QFN33 package and is specified for operation over the -40C to +85C temperature range.
* * * * * * * * * * * *
Applications
* * * * * * Cellular Phones / Smart Phones Digital Cameras Handheld Instruments Micro Hard Disc Drives Microprocessor / DSP Core / IO Power PDAs and Handheld Computers
Typical Application
Input: 2.7V to 5.5V
CIN 1F
VIN1 VIN2 VCC
L1 LX1 FB1 L2 LX2 2.2H VOUT2 R3
C1 4.7F
VOUT1 R1
C2 4.7F
2.2H
AAT2713
MODE/SYNC PS EN1 EN2
R2
FB2 R4
AGND
PGND1 PGND2
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Pin Descriptions
Pin #
1 2 4, 3 5, 16 6, 15 7, 14 8, 13
Low Noise Dual 600mA Step-Down Converter with Synchronization
Symbol
PS AGND FB1, FB2 VIN1, VIN2 N/C LX1, LX2 PGND1, PGND2
Function
Phase shift pin. Logic high enables the PS feature which forces the two converters to operate 180 out of phase when both are in forced PWM mode. Analog ground. Return the feedback resistive divider to this ground. See section on PCB layout guidelines and evaluation board layout diagram. Feedback input pins. An external resistive divider ties to each and programs the respective output voltage to the desired value. Input supply voltage pins. Must be closely decoupled to the respective PGND. Not connected Output switching nodes that connect to the respective output inductor. Main power ground return. Connect to the input and output capacitor return. See section on PCB layout guidelines and evaluation board layout diagram. Converter enable input pins. A logic high enables the converter channel. A logic low forces the channel into shutdown mode, reducing the channel supply current to less than 1A. This pin should not be left floating. When not actively controlled, this pin can be tied directly to VIN and/ or VCC. Control circuit power supply. Connect to the higher voltage of VIN1 or VIN2. Logic low enables light load mode operation for light loads and fixed-frequency PWM operation for heavy loads. Logic high forces low noise PWM operation under all operating conditions. Connect to an external clock for synchronization (PWM only). Exposed paddle (bottom). Use properly sized vias for thermal coupling to the ground plane. See section on PCB layout guidelines.
10, 9 11 12 EP
EN1, EN2 VCC MODE/SYNC
Pin Configuration
QFN33-16 (Top View)
PGND2 LX2 N/C VIN2
16 15 14 13
PS AGND FB2 FB1
1 2 3 4 5 6 7 8
12 11 10 9
MODE/SYNC VCC EN1 EN2
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PGND1 LX1 N/C VIN1
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Absolute Maximum Ratings1
TA = 25C unless otherwise noted. Symbol
VINX VN TJ TS TLEAD
Description
[VIN1, VIN2] to GND [VCC, EN1, EN2, FB1, FB2, MODE/SYNC, PS, LX1, LX2] to GND Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 -0.3 to VINX + 0.3 -40 to 150 -65 to 150 300
Units
V V C C C
Thermal Information
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation
Value
50 2
Units
C/W W
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.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics1
VIN = VCC = 3.6V, TA = -40C to +85C, unless noted otherwise. Typical values are at TA = 25C. Symbol
Power Supply VCC, VIN1, VIN2 UVLO IQ ISHDN Each Converter VOUT VOUT IFB ILIM RDS(ON)H RDS(ON)L VOUT/ VOUT/IOUT VOUT/ VOUT/VIN VFB FOSC TS Logic TSD THYS VIL VIH IEN, IMODE/SYNC, IPS Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis EN, MODE/SYNC, PS Logic Low Threshold EN, MODE/SYNC, PS Logic High Threshold Logic Input Current VIN = VFB = 5.5V 140 15 0.6 1.5 -1.0 1.0 C C v V A
Description
Input Voltage Under-Voltage Lockout Quiescent Current Shutdown Current Output Voltage Tolerance Output Voltage Range Feedback Leakage P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance Load Regulation Line Regulation Feedback Threshold Voltage Accuracy Oscillator Frequency Start-Up Time
Conditions
Min
2.7
Typ
Max
5.5 2.7
Units
V V A A % V A A %/mA %/V
VCC Rising VCC Falling VEN1 = VEN2 = VFB1 = VFB2 = VCC, No Load EN1 = EN2 = GND IOUT = 0 to 600mA, VIN = 3.0 to 5.5V IOUT = 0 to 450mA, VIN = 2.7 to 5.5V VFB = 1.0V Each Converter -3.0 0.6
2.35 70
140 1.0 -3.0 VIN 0.2
1.5 0.45 0.40 0.002 0.125 0.591 0.600 1.7 0.609
ILOAD = 0 to 600 mA VIN = 2.7 to 5.5V, ILOAD = 100 mA No Load, TA = 25C From Enable to Output Regulation; Both Channels
V MHz s
150
1. The AAT2713 guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization and correlation with statistical process controls.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
Efficiency vs. Load
(VOUT = 3.3V; L = 4.7H; LL/PWM Mode)
100 90 1.0
Load Regulation
(VIN = 4.2V to 5.5V; VOUT = 3.3V; L = 4.7H; LL/PWM Mode)
Efficiency (%)
80 70 60 50 40 30 20 10 0.1 1 10 100
Output Error (%)
0.5
0.0
VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
1000
-0.5
-1.0 0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 4.7H; LL/PWM Mode)
100 90 1.0
Load Regulation
(VIN = 2.7V to 5.5V; VOUT = 2.5V; L = 3.3H; LL/PWM Mode)
Output Error (%)
Efficiency (%)
80 70 60 50 40 30 20 0.1 1 10 100
0.5
VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
1000
0.0
-0.5
-1.0 0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.8V; L = 2.2H; LL/PWM Mode)
100 90 1.0
Load Regulation
(VIN = 2.7V to 5.5V; VOUT = 1.8V; L = 2.2H; LL/PWM Mode)
Efficiency (%)
80 70 60 50 40 30 20 10 0.1 1 10 100 1000
Output Error (%)
0.5
VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
0.0
-0.5
-1.0 0.1 1 10 100 1000
Output Current (mA)
Output Current (mA)
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
Efficiency vs. Load
(VOUT = 1V; L = 1.2H; LL/PWM Mode)
100 90
Line Transient
(VIN = 3.6V to 4.6V; VOUT = 1.8V; IOUT = 600mA; COUT = 4.7F) Output Voltage (AC coupled) (bottom) (V) Input Voltage (top) (V)
5 4 3 1.85 1.80 1.75
Efficiency (%)
80 70 60 50 40 30 20 10 0.1 1 10 100 1000
VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
Output Current (mA)
Time (200s/div)
Switching Frequency vs. Temperature
(VIN = 3.6V; IOUT = 600mA) Switching Frequency (MHz)
1.74 1.72 1.70 1.68 1.66 1.64 1.62 1.60 1.58 -40 -20 0 20 40 60 80 100 2
Switching Frequency vs. Input Voltage
(IOUT = 600mA)
VOUT = 2.5V
Frequency Variation (%)
1
VOUT = 1.8V
0 -1 -2 -3 -4 2.7
VOUT = 1.0V
VOUT = 1.2V VOUT = 2.5V
3.1 3.5 3.9 4.3
VOUT = 3.3V
4.7 5.1 5.5
Temperature (C)
Input Voltage (V)
No Load Quiescent Current vs. Input Voltage
(VEN1 = VEN2 = VIN)
90 900
P-Channel RDS(ON) vs. Input Voltage
120C
Quiescent Current (A)
80
85C RDS(ON) (m)
800 700 600 500 400 300 2.5
100C
85C
70
25C
60
-40C
50
25C
3 3.5 4 4.5 5 5.5 6
40 2.5
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Input Voltage (V)
6
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
N-Channel RDS(ON) vs. Input Voltage
700
Logic High Threshold (VIH) vs. Input Voltage
1.3
120C
600
100C VIH (V)
1.2 1.1
RDS(ON) (m)
500 1.0 0.9 0.8 400 300 200 100 2.5
-40C
25C
3 3.5
85C
0.7 0.6 2.5
25C
85C
4
4.5
5
5.5
6
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Logic Low Threshold (VIL) vs. Input Voltage
1.2 1.1 1.0
0.8
Line Regulation
(VOUT = 1.8V; L = 2.2H)
Output Accuracy (%)
0.4
-40C
IOUT = 10mA to 600mA
VIL (V)
0.9 0.8 0.7 0.6 2.5
0.0
25C
3.0 3.5 4.0
85C
4.5 5.0 5.5 6.0
-0.4
IOUT = 0.1mA
-0.8 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
Input Voltage (V)
Line Regulation
(VOUT = 1V; L = 1.2H)
0.4 1.0
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 2.5V) Output Voltage Error (%)
Output Accuracy (%)
0.2
IOUT = 0.1mA to 600mA
0.5
IOUT = 600mA
0.0
0.0
IOUT = 0.1mA
-0.5
-0.2
-0.4 2.5
-1.0 3.0 3.5 4.0 4.5 5.0 5.5 -40 -15 10 35 60 85
Input Voltage (V)
Temperature (C)
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
1.0 1.0
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 1V) Output Voltage Error (%)
Output Voltage Error (%)
0.5
0.5
IOUT = 600mA
0.0
IOUT = 0.1mA
0.0
IOUT = 0.1mA
-0.5
-0.5
IOUT = 600mA
-15 10 35 60 85
-1.0 -40
-1.0 -40 -15 10 35 60 85
Temperature (C)
Temperature (C)
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 600mA) Enable Voltage (top) (V) Output Voltage (middle) (V) Enable Voltage (top) (V) Output Voltage (middle) (V)
4 2 4 2
Soft Start
(VIN = 3.6V; VOUT = 1.2V; IOUT = 600mA)
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
0 2 1 0 1.0 0.5 0.0
0 2 1 0 1.0 0.5 0.0
Time (100s/div)
Time (100s/div)
Load Transient
(1mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF Open) Output Voltage (AC coupled) (top) (V)
2.3
Load Transient
(1mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF = 100pF) Output Voltage (AC coupled) (top) (V)
2.3
Output Current (bottom) (A)
Output Current (bottom) (A)
1.8 1.3
1.8 1.3
0.5 0.0
0.5 0.0
Time (50s/div)
Time (50s/div)
8
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
Load Transient
(450mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF Open) Output Voltage (AC coupled) (top) (V)
1.85
Load Transient
(450mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF = 100pF) Output Voltage (AC coupled) (top) (V)
1.85
Output Current (bottom) (A)
Output Current (bottom) (A)
1.80 1.75
1.80 1.75
0.6 0.4
0.6 0.4
Time (50s/div)
Time (50s/div)
Load Transient
(1mA to 600mA; VIN = 3.6V; VOUT = 1.2V; COUT = 4.7F; CFF Open) Output Voltage (AC coupled) (top) (V) Output Voltage (AC coupled) (top) (V)
1.7 1.7
Load Transient
(1mA to 600mA; VIN = 3.6V; VOUT = 1.2V; COUT = 4.7F; CFF = 100pF)
Output Current (bottom) (A)
Output Current (bottom) (A)
1.2 0.7
1.2 0.7
0.5 0.0
0.5 0.0
Time (50s/div)
Time (50s/div)
Line Transient
(VIN = 3.6V to 4.6V; VOUT = 1.8V; IOUT = 600mA; COUT = 4.7F) Output Voltage (AC coupled) (bottom) (V) Input Voltage (top) (V) Input Voltage (top) (V)
5 4 3 1.85 1.80 1.75 5 4 3
Line Transient
(VIN = 3.6V to 4.6V; VOUT = 1.2V; IOUT = 600mA; COUT = 4.7F) Output Voltage (AC coupled) (bottom) (V)
1.25 1.20 1.15
Time (200s/div)
Time (200s/div)
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Electrical Characteristics
Input Voltage Ripple
(CIN = 2 x 10F; VIN = 3.6V; VOUT1 = 1.8V; VOUT2 = 2.5V; IOUT1,2 = 600mA; 0 Phase Shift; PS Logic Low)
3.62
Input Voltage Ripple
(CIN = 2 x 10F; VIN = 3.6V; VOUT1 = 1.8V; VOUT2 = 2.5V; IOUT1,2 = 600mA; 180 Phase Shift; PS Logic High) Input Voltage (top) (V)
3.61
Input Voltage (top) (V)
3.61 3.60 3.59 4 LX1 0 4 LX2 0
Switching Voltage LX1, LX2 (V)
Switching Voltage LX1, LX2 (V)
3.60 3.59 4 LX1 0
4 LX2 0
Time (0.2s/div)
Time (0.2s/div)
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 600mA) Inductor Current (bottom) (A) Output Voltage (AC coupled) (top) (V))
1.82 1.80 1.78 0.8 0.6 0.4
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.2V; IOUT = 600mA) Inductor Current (bottom) (A) Output Voltage (AC coupled) (top) (V)
1.22 1.20 1.18 0.8 0.6 0.4
Time (500ns/div)
Time (500ns/div)
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA) Inductor Current (bottom) (A) Output Voltage (AC coupled) (top) (V) Output Voltage (AC coupled) (top) (V)
1.82 1.80 1.78 1.22 1.20 1.18
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.2V; IOUT = 1mA) Inductor Current (bottom) (A)
0.4 0.2 0.0
0.4 0.2 0.0
Time (20s/div)
Time (20s/div)
10
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Functional Block Diagram
FB1 VCC VIN1
Err. Amp. Voltage Reference
Comp
DH
Logic
LX1
DL
EN1 AGND
Control Logic
PGND1 VIN2
Oscillator
MODE/SYNC PS FB
Comp . DH
Err. Amp.
LX2
Logic
DL
Voltage Reference
EN2
Control Logic
PGND2
Functional Description
The AAT2713 is a peak current mode pulse width modulated (PWM) converter with internal compensation. Each channel has independent input, enable, feedback, and ground pins with a 1.7MHz clock. Both converters operate in either a fixed-frequency (PWM) mode under all load conditions or a light load (LL) mode operation for light loads combined with PWM mode operation for heavy loads. The AAT2713 also produces reduced ripple and spectral noise due to a low noise architecture. A phase shift pin programs the converters to operate in phase or 180 out of phase. The converter can also be synchronized to an external clock during PWM operation. The input voltage range is 2.7V to 5.5V. An external resistive divider as shown in Figure 1 programs the output voltage up to the input voltage. The converter MOSFET power stage is sized for 600mA load capability with up to 96% efficiency. Light load efficiency is up to 90% for a 1mA load.
Soft-Start / Enable
The AAT2713 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 (shutdown) with a bias current of less than 1A.
Low Dropout Operation
For conditions where the input voltage drops to the output voltage level, the converter duty cycle increases to 100%. As the converter approaches the 100% duty cycle, the minimum off time initially forces the high side on time to exceed the 1.7MHz clock cycle and reduce the effective switching frequency. Once the input drops below the level where the converter can regulate the output, the high side P-channel MOSFET is enabled continuously for 100% duty cycle. At 100% duty cycle the output voltage tracks the input voltage minus the I*R drop of the high side P-channel MOSFET.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
VIN
Low Noise Dual 600mA Step-Down Converter with Synchronization
C3 4.7F
U1 AAT2713
5 10 11
VIN1 EN1 VCC LX1 FB1 N/C AGND PGND1
VIN2 EN2 PS LX2 FB2 MODE/SYNC N/C PGND2
16 9 1 14 3 12 15 13
1.8V L1 2.2H R1 118k C1 4.7F R2 59.0k
2.5V L2 3.3H R3 187k R4 59.0k C2 4.7F
7 4 6 2 8
Figure 1: AAT2713 Typical Schematic.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. When the input voltage falls below 2.35V (typ) the AAT2713 will stop regulation of the output.
PWM/LL Operation
For minimum ripple under light load conditions, the MODE/SYNC pin should be tied to a logic high. For more efficient operation under light load conditions the MODE/ SYNC pin should be tied to a logic low level. When MODE/SYNC is logic high, the AAT2713 operates in fixed-frequency mode under all load conditions. When MODE/SYNC is logic low, the AAT2713 operates in fixedfrequency PWM mode under heavy loads and light load mode under light loads.
Fault Protection
For overload conditions, the peak inductor current is limited. Thermal protection disables the converter when the internal dissipation or ambient temperature becomes excessive. The over-temperature threshold for the junction temperature is 140C with 15C of hysteresis.
Converter Clock Phase
A logic high on the PS pin while in PWM mode forces both converters to operate 180 out of phase thus reducing the input ripple by roughly half. A logic low on the PS pin synchronizes both converters in phase.
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2713.2008.01.1.0
PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
At full load the inductor DC loss is 35mW which corresponds to a 3.2% loss in efficiency for a 600mA, 1.8V output.
Applications Information
Inductor Selection
The step down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low voltage fixed versions of the AAT2713 is 0.6A/sec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 2.2H inductor.
Input Capacitor
A key feature of the AAT2713 is that the fundamental switching frequency ripple at the input can be reduced by operating the two converters 180 out of phase. This reduces the input ripple by roughly half, reducing the required input capacitance. An X5R ceramic input capacitor as small as 1F is often sufficient. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage.
m= L=
0.75 VO 0.75 1.8V A = = 0.6 L 2.2H sec 0.75 VO 0.75V VO s 1.2 A VO = A m 0.6 s s 2.5V = 3.1H A
CIN =
V VO 1- O VIN VIN
VPP - ESR FS IO
= 1.2
This equation provides an estimate for the input capacitor required for a single channel. The equation below solves for the input capacitor size for both channels. It makes the worst case assumption that both converters are operating at 50% duty cycle with in phase synchronization.
In this case a standard 3.3H value is selected. Table 1 displays the suggested inductor values for the AAT2713. 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 inductor's saturation characteristics. The inductor should not show any appreciable saturation under all 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. The 2.2uH CDRH2D11 series inductor selected from Sumida has a 98m DCR and a 1.27A DC current rating.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
Because the AAT2713 channels will generally operate at different duty cycles the actual ripple will vary and be less than the ripple (VPP) used to solve for the input capacitor in the above equation. Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10F 6.3V X5R ceramic capacitor with 5V DC applied is actually about 6F. Inductor
1.0H - 1.5H 2.2H 3.3H 4.7H 2.2H
Configuration
0.6V adjustable with external resistive divider Fixed output voltage
Output Voltage
0.6V - 1.3V 1.4V - 1.8V 2.0V - 2.8V 3.3V 0.6V - 3.3V
Slope Compensation
0.6A/s NA
Table 1: Inductor Values.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Since the inductance of a short printed circuit board 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 inductance cannot be reduced to a level that does not effect the converter performance, a high ESR tantalum or aluminum electrolytic (C10 of Figure 2) should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system.
The maximum input capacitor RMS current is:
IRMS = IO1 *
VO1 V * 1 - O1 + IO2 * VIN VIN
VO2 V * 1 - O2 VIN 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 of both converters combined.
IRMS(MAX) =
IO1(MAX) + IO2(MAX) 2
Output Capacitor
The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7F to 10F X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current the ceramic output capacitor alone supplies the load current until the loop responds. As the loop responds the inductor current increases to match the load current demand. This typically takes several switching cycles and can be estimated by:
This equation also makes the worst-case assumption that both converters are operating at 50% duty cycle synchronized. The term V * 1 - V appears in both the input voltage ripple and input capacitor RMS current equations. It is at maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle.
IN IN
VO
VO
VO V * 1 - O = D (1 - D) = 0.52 = 0.25 VIN VIN
The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2713. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize the stray inductance, the capacitor should be placed as close 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 (C3 and C9) can be seen in the evaluation board layout in Figures 3 and 4. Since decoupling must be as close to the input pins as possible it is necessary to use two decoupling capacitors, one for each converter. A Laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation 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 effect the converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result.
COUT =
3 * ILOAD VDROOP * FS
Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7F. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater phase margin. The maximum output capacitor RMS ripple current is given by:
IRMS(MAX) =
VOUT * (VIN(MAX) - VOUT) L * F * VIN(MAX) 2* 3 *
1
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Thermal Calculations
There are three types of losses associated with the AAT2713 converter: switching losses, conduction losses, and quiescent current losses. Of the three types of losses, conduction losses are overwhelmingly dominant. The conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. The switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the dual converter losses is given by calculating conduction losses::
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.
Adjustable Output Resistor Selection
Resistors R1 through R4 of Figure 1 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string, the minimum suggested value for R2 and R4 is 59k. Although a larger value will reduce the quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistor values for various output voltages with R2 and R4 set to either 59k for good noise immunity or 221k for reduced no load input current.
PTOTAL =
IO12 * (RDSON(HS) * VO1 + RDSON(LS) * [VIN -VO1]) VIN IO22 * (RDSON(HS) * VO2 + RDSON(LS) * [VIN -VO2]) VIN
VOUT 1.5V R1 = V -1 * R2 = 0.6V - 1 * 59k = 88.5k REF
With an external feedforward capacitor (C4 and C5 of Figure 2) the AAT2713 delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor (C1 and C2) for stability. R2, R4 = 59k R1, R3 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 265
+
For the condition where channel one is in dropout at 100% duty cycle the total device dissipation reduces to:
PTOTAL = IO12 * RDSON(HS) IO22 * (RDSON(HS) * VO2 + RDSON(LS) * [VIN -VO2]) VIN
VOUT (V)
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3
R2, R4 = 221k R1, R3 (k)
75 113 150 187 221 261 301 332 442 464 523 715 1000
+
Given the total losses, the maximum junction temperature can be derived from the JA for the QFN33-12 package which is 28C/W to 50C/W minimum.
TJ(MAX) = PTOTAL * JA + TAMB
Table 2: Feedback Resistor Values.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
PCB Layout
Low Noise Dual 600mA Step-Down Converter with Synchronization
3. The feedback trace should be separate from any power trace and connect as close as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. Place the external feedback resistors as close as possible to the FB pin. This prevents noise from being coupled into the high impedance feedback node. Keep the resistance of the trace from the load return to GND to a minimum. This minimizes any error in DC regulation due to potential differences of the internal signal ground and the power ground. For good thermal coupling, PCB vias are required from the pad for the QFN package's exposed pad to the ground plane. The via diameter should be 0.3mm to 0.33mm and positioned on a 1.2 mm grid.
Use the following guidelines to insure a proper layout: 1. Due to the pin placement of VIN for both converters, proper decoupling is not possible with just one input capacitor. The input capacitors C3 and C9 should connect as closely as possible to the respective VIN and GND as shown in Figure 3. Connect the output capacitor and inductor as closely as possible. The connection of the inductor to the LX pin should also be as short as possible.
4.
2.
5.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Design Example
Specifications
VO1 VO2 VIN FS TAMB
Low Noise Dual 600mA Step-Down Converter with Synchronization
2.5V @ 600mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA 1.8V @ 600mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA 2.7V to 4.2V (3.6V nominal) 1.7 MHz 85C
1.8V VO1 Output Inductor
L1 = 1.2 s s VO1 = 1.2 1.8V = 2.16H; use 2.2H (see table 1). A A
For Sumida CDRH2D11 2.2H DCR = 98m.
I1 =
1.8V VO1 VO1 1.8V 1= 1= 275mA L F VIN 2.2H 1.7MHz 4.2V
IPK1 = IO1 +
I1 = 0.6A + 0.1375A = 0.7375A 2
PL1 = IO12 DCR = 0.6A2 98m = 35mW
2.5V VO2 Output Inductor
L1 = 1.2 s s VO2 = 1.2 2.5V = 3H; use 3.3H (see table 1). A A
For Sumida inductor CDRH2D11 3.3H DCR = 123m.
I2 =
2.5V VO2 VO2 2.5V 1= 1= 180mA L F VIN 3.3H 1.7MHz 4.2V
IPK2 = IO2 +
I2 = 0.6A + 0.090A = 0.690A 2
PL2 = IO22 DCR = 0.6A2 123m = 44mW
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
1.8V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 2.65F; use 4.7F 0.2V * 1.7MHz VDROOP * FS 1 2* 3 * (VOUT) * (VIN(MAX) - VOUT) 1 1.8V * (4.2V - 1.8V) * = 79mARMS = L * F * VIN(MAX) 2 * 3 2.2H * 1.7MHz * 4.2V
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (79mA)2 = 31.5W
2.5V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 2.65F; use 4.7F VDROOP * FS 0.2V * 1.7MHz (VOUT) * (VIN(MAX) - VOUT) 1 2.5V * (4.2V - 2.5V) * = 52mARMS = L * F * VIN(MAX) 2 * 3 3.3H * 1.7MHz * 4.2V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (52mA)2 = 13.6W
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
=
1 = 9.29F; use 10F 25mV - 5m * 4 * 1.7MHz 1.2A
IRMS(MAX) =
IO1 + IO2 = 0.6ARMS 2
P = esr * IRMS2 = 5m * (0.6A)2 = 1.8mW
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
AAT2713 Losses
Low Noise Dual 600mA Step-Down Converter with Synchronization
The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an 85C ambient and a 120C junction temperature.
PTOTAL =
IO12 * (RDSON(HS) * VO1 + RDSON(LS) * (VIN -VO1)) + IO22 * (RDSON(HS) * VO2 + RDSON(LS) * (VIN -VO2)) VIN 0.62 * (0.725 * 2.5V + 0.55 * (2.7V - 2.5V)) + 0.62 * (0.725 * 1.8V + 0.55 * (2.7V - 1.8V))
=
2.7V
= 496mW
TJ(MAX) = TAMB + JA * PLOSS = 85C + (50C/W) * 496mW = 110C TJ(MAX) = TAMB + JA * PLOSS = 85C + (28C/W) * 496mW = 99C
3 2 1
Phase Shift
VIN
6
U1 AAT2513/AAT2713
N/C VP2 PS AGND FB2 FB1 VP1 LX1 N/C LX2 PGND2 SYNC VCC EN1 EN2 PGND1 15 14 13 12 11 10 9 8
LX2 L2 C2 4.7F
VO2
VIN
VIN C5 100pF R3
C4 100pF
VIN
R1
16 1 2 3 4
Sync
C7 1F
1 2 3
VCC LX1 L1 C8 0.1F C1 4.7F C6 1F VO1
C10 120F
5 7
C10 is OPTIONAL
R4 59.0k
R2 59.0k
C9 4.7F
C3 4.7F
GND
R5 10
321 321
VIN
VCC
Output 2
Output 1
L1/L2: 744028XXX Wurth Elektronik or CDRH2D11/HP Sumida
Figure 2: AAT2713 Evaluation Board Schematic1.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10F.
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PRODUCT DATASHEET
AAT2713
L1, L2 (H)
1.0 - 1.5 1.0 - 1.5 1.0 - 1.5 1.0 - 1.5 1.0 - 1.5 1.0 - 1.5 2.2 2.2 2.2 2.2 3.3 3.3 4.7
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
R2 and R4 = 59k R1, R3 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 265
Adjustable Version (0.6V device) VOUT (V)
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3
R2 and R4 = 221k1 R1, R3 (k)
75.0 113 150 187 221 261 301 332 442 464 523 715 1000
Fixed Version VOUT (V)
0.6-3.3
R2, R4 arenot used R1, R3 (k)
zero
L1, L2 (H)
2.2
Table 5: Evaluation Board Component Values.
Figure 3: AAT2713 Evaluation Board Top Side.
Figure 4: AAT2713 Evaluation Board Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221k.
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PRODUCT DATASHEET
AAT2713
Type
Shielded Shielded Shielded Shielded Wire Wound Chip Wire Wound Chip Wire Wound Chip Wire Wound Chip Shielded Shielded Shielded Shielded
SystemPowerTM
Manufacturer
Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden Wurth Elektronik Wurth Elektronik Wurth Elektronik Wurth Elektronik
Low Noise Dual 600mA Step-Down Converter with Synchronization
Part Number
CDRH2D11 CDRH2D11 CDRH2D11 CDRH2D11 CBC2518T CBC2518T CBC2518T CBC2016T 744028001 744028002 744028003 744028004
Inductance (H)
1.5 2.2 3.3 4.7 1.0 2.2 4.7 2.2 1.0 2.2 3.3 4.7
Max DC Current (A)
1.48 1.27 1.02 0.88 1.2 1.1 0.92 0.83 1.5 1.0 0.85 0.7
DCR ()
0.068 0.098 0.123 0.170 0.08 0.13 0.2 0.2 0.065 0.125 0.185 0.265
Size (mm) LxWxH
3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 2.5x1.8x1.8 2.5x1.8x1.8 2.5x1.8x1.8 2.0x1.6x1.6 2.8x2.8x1.1 2.8x2.8x1.1 2.8x2.8x1.1 2.8x2.8x1.1
Table 4: Typical Surface Mount Inductors. Manufacturer
AVX Murata Murata Murata Taiyo-Yuden TDK TDK
Part Number
0603ZD225K GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39 LMK107BJ475K C1608X5R1C225K C1608X5R1A475K
Value
2.2F 4.7F 10F 22F 4.7F 2.2F 4.7F
Voltage
10V 10V 6.3V 6.3V 10V 16V 10V
Temp. Co.
X5R X5R X5R X5R X5R X5R X5R
Case
0603 0805 0805 0805 0603 0603 0603
Table 5: Surface Mount Capacitors.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Ordering Information
Voltage Package
QFN33-16 Channel 1 0.6V Channel 2 0.6V
Marking1
UFXYY
Part Number (Tape and Reel)2
AAT2713IVN-AA-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx.
Legend Voltage
Adjustable (0.6V) 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3
Code
A G I Y N O P Q R S T W
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Package Information1
QFN33-16
Pin 1 Dot By Marking Pin 1 Identification
1
0.230 0.050
0.500 0.050
5
3.000 0.050
C0.3
0.400 0.100
13 9
3.000 0.050
1.250 0.050
Top View
Bottom View
1.250 0.050 0.214 0.036 0.900 0.100
0.025 0.025
Side View
All dimensions in millimeters.
1. 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.
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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