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AAT2513
Dual 600mA Step-Down Converter with Synchronization General Description
The AAT2513 is a high efficiency dual synchronous step-down 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. 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 60A, 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 AAT2513 is available in a Pb-free, thermally enhanced 16-pin QFN33 package and is specified for operation over the -40C to +85C temperature range.
Features
* *
SystemPowerTM
* * * * * * * * * * * *
VIN Range: 2.7V to 5.5V Output Current: -- Channel 1: 600mA -- Channel 2: 600mA 96% Efficient Step-Down Converter Low No Load Quiescent Current -- 60A 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
Applications
* * * * * * Cellular Phones / Smart Phones Digital Cameras Handheld Instruments Micro Hard Disc Drives Microprocessor / DSP Core / IO Power PDAs and Handheld Computers
Typical Application
VIN1 VIN2 VCC FB1 L1 VOUT1 LX1 2H L2 LX2 2H MODE/SYNC PS EN1 EN2 AGND PGND1 PGND2 FB2 R4 R3
C1 4.7F
Input: 2.7V to 5.5V
CIN 1F
R1 VOUT2
AAT2513
R2
C2 4.7F
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Pin Descriptions
Pin #
1 2 4, 3 5, 6, 7, 8, 16 15 14 13
Symbol
PS AGND FB1, FB2 VIN1, VIN2 N/C LX1, LX2 PGND1, PGND2 EN1, EN2
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 automatic light load mode for optimized efficiency throughout the entire load range. 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
VCC MODE/SYNC
EP
Pin Configuration
QFN33-16 (Top View)
PGND2 LX2 N/C VIN2
16 15 14 13
PS AGND FB2 FB1
1 2 3 4
12 11 10 9
MODE/SYNC VCC EN1 EN2
5
6
7
8
PGND1 LX1 N/C VIN1
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Absolute Maximum Ratings1
TA = 25C unless otherwise noted. Symbol
VIN1/2 GND, PGND1/2 EN1/2, SYNC, LX1/2, FB1/2, PS TJ TS TLEAD
Description
Input Voltage Ground Pins Maximum Rating Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 -0.3 to +0.3 -0.3 to VCC + 0.3 -40 to 150 -65 to 150 300
Units
V 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. 2513.2007.04.1.1
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AAT2513
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 Description Conditions Min Typ Max Units
Power Supply VCC, Input Voltage VIN1, VIN2 UVLO Under-Voltage Lockout VCC Rising VCC Falling VEN1 = VEN2 = VCC, No Load EN1 = EN2 = GND IOUT = 0 to 600mA, VIN = 2.9 to 5.5V IOUT = 0 to 450mA, VIN = 2.7 to 5.5V VIN Open, VLX = 5.5V, EN = GND VIN = 5.5V, VLX = 0 to VIN VFB = 1.0V Each Converter
2.7
5.5 2.7 2.35 60 120 1.0
V V A A
IQ Quiescent Current ISHDN Shutdown Current Each Converter VFB VOUT ILX_LEAK ILX_LEAK 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 Feedback Voltage Tolerance Output Voltage Range LX Reverse Leakage Current (Fixed) LX Leakage Current 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
-3.0 0.6
-3.0 VIN 1.0 1.0 0.2 1.0 0.45 0.40 0.002 0.125
% V A A A A %/mA %/V V MHz s
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
0.591 0.600 0.609 1.7 150
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 1.4
C C V V
-1.0
1.0
A
1. The AAT2513 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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AAT2513
Dual 600mA Step-Down Converter with Synchronization Electrical Characteristics
Efficiency vs. Load
(VOUT = 3.3V; L = 4.7H; LL Mode)
100 90 1.00
DC Regulation
(VIN = 5.0V; VOUT = 3.3V; L = 4.7H; LL Mode)
0.75
VIN = 3.6V
Output Error (%)
Efficiency (%)
80 70 60 50 40 30 0.1 1 10 100 1000
0.50 0.25 0.00 -0.25 -0.50 -0.75 -1.00 0.1 1 10 100 1000
VIN = 4.2V VIN = 5.0V
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 3.3H; LL Mode)
100 90 2.0
DC Regulation
(VIN = 3.3V to 5.5V; VOUT = 2.5V; L = 3.3H; LL Mode)
1.5
VIN = 2.7V
Output Error (%)
Efficiency (%)
80 70 60 50 40 30 0.1 1 10 100 1000
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1 1 10 100 1000
VIN = 3.6V VIN = 4.2V VIN = 5.0V
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.8V; L = 2.2H; LL Mode)
100 90 1.0 0.8
DC Regulation
(VOUT = 1.8V; L = 2.2H; LL Mode)
VIN = 2.7V
Efficiency (%)
80 70 60 50 40 30 20 0.1 1 10 100 1000
Output Error (%)
0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 1 10
VIN = 5.0V VIN = 4.2V
VIN = 3.6V VIN = 4.2V VIN = 5.0V
VIN = 3.3V
100
1000
Output Current (mA)
Output Current (mA)
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Electrical Characteristics
Efficiency vs. Load
(VOUT = 1.5V; L = 2.2H; LL Mode)
100 90 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 1 10 100 1000 0.1 1 10 100 1000
DC Regulation
(VOUT = 1.5V; L = 2.2H; LL Mode)
Efficiency (%)
80 70 60 50 40 30 20
Output Error (%)
VIN = 2.7V
VIN = 3.3V VIN = 4.2V VIN = 5.0V
VIN = 3.6V VIN = 4.2V
Output Current (mA)
Output Current (mA)
Switching Frequency vs. Temperature
Switching Frequency (MHz)
1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 -40 4
Switching Frequency vs. Input Voltage
(IOUT = 600mA; 25C)
VIN = 4.2V
Frequency Variation (%)
3 2 1 0 -1 -2 -3 -4
VOUT = 1.5V
VOUT = 1.8V
VIN = 3.6V
VIN = 2.5V
VIN = 3.3V
-20
0
20
40
60
80
100
120
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Temperature (C)
Input Voltage (V)
Output Voltage Error Vs. Temperature
(VOUT = 2.5V; IOUT = 600mA)
0.30
No Load Quiescent Current vs. Input Voltage
70
Output Voltage Error (%)
Input Current (A)
0.25 0.20 0.15 0.10 0.05 0.00 -40
VIN = 3.6V
65 60 55 50 45 2.5
85C 25C
VIN = 4.2V
-40C
-20
0
20
40
60
80
100
120
3
3.5
4
4.5
5
5.5
6
Temperature (C)
Input Voltage (V)
6
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Electrical Characteristics
P-Channel RDS(ON) vs. Input Voltage
1000 900 1.3
VIH vs. Input Voltage
120C 100C 85C
1.2 1.1
RDS(ON) (m)
800 700 600 500 400 300 2.5
-40C
25C
VIH (V)
1.0 0.9 0.8
85C
25C
3 3.5 4 4.5 5 5.5 6
0.7 0.6 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Input Voltage (V)
Input Voltage (V)
VIL vs. Input Voltage
Enable Voltage (top) (V) Output Voltage (middle) (V)
1.2 1.1 1.0 0.9 0.8 0.7 0.6 2.5 4 3 2 1 0
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 600mA)
Inductor Current (bottom) (A)
VIL (mV)
-40C
25C
0.6 0.4 0.2 0.0 -0.2
85C
3.0 3.5 4.0 4.5 5.0 5.5 6.0
Input Voltage (V)
Time (50s/div)
Load Transient
(1mA to 450mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F)
Load Current (middle) (A) Inductor Current (bottom) (A) Output Voltage (top) (V)
2.0 1.8
Load Transient
(1mA to 450mA; VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 100pF)
Load Current (middle) (A) Inductor Current (bottom) (A)
Output Voltage (AC) (top) (V)
2.0 1.8 1.6
450mA 1mA 0.5 0
450mA 1mA 0.5 0.0 -0.5
Time (20s/div)
Time (20s/div)
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Electrical Characteristics
Load Transient
(5mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F)
Load Transient
(1mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 100pF)
Load Current (middle) (A) Inductor Current (bottom) (A)
Load Current (middle) (A) Inductor Current (bottom) (A)
2.8
2.0
Output Voltage (top) (V)
Output Voltage (top) (V)
2.3 1.8 1.3 600mA 5mA 1.0 0.5 0.0 -0.5
1.8 1.6 600mA 1mA 0.5 0
Time (40s/div)
Time (40s/div)
Load Transient
(450mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F)
Load Transient
(450mA to 600mA; VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 100pF
Load Current (middle) (A) Inductor Current (bottom) (A)
Output Voltage (AC) (top) (V)
2.0
2.0 1.9 1.8 1.7 600mA 450mA 0.6 0.4 0.2
Load Current (middle) (A) Output Current (bottom) (A)
Output Voltage (top) (V)
1.8 1.6 600mA 450mA
0.6 0.4 0.2
Time (20s/div)
Time (20s/div)
Line Transient
(VIN = 3.6V to 4.2V; VOUT = 1.8V; IOUT = 600mA; COUT = 4.7F)
5
Output Voltage (bottom) (V)
Input Voltage (top) (V)
4 3 2 1 1.84 1.82 1.80 1.78 1.76 1.74
Time (40s/div)
8
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Electrical Characteristics
Line Regulation
(VOUT = 1.8V; L = 2.2H)
1.0 0.5 2.0 1.5
Line Regulation
(VOUT = 1.5V; L = 2.2H)
Accuracy (%)
0.0 -0.5 -1.0 -1.5 -2.0 2.5
Accuracy (%)
IOUT = 0.1mA to 100mA
1.0 0.5 0.0 -0.5 -1.0 -1.5
IOUT = 0.1mA to 100mA
IOUT = 400mA
IOUT = 400mA
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-2.0 2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Output Voltage Ripple
(VOUT = 1.8V; VIN = 3.6V; Load = 1mA)
Output Voltage Ripple
(VOUT = 1.8V; VIN = 3.6V; Load = 600mA)
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
Output Voltage (top) (V)
Output Voltage (top) (V)
1.85 1.80 1.75
1.82 1.80 1.78
0.2 0.1 0.0 -0.1
0.7 0.6 0.5 0.4
Time (10s/div)
Time (0.2s/div)
Input Ripple
(CIN = 2 x 10F; VIN = 3.6V; VOUT1 = 1.8V; VOUT2 = 2.5V; IOUT1,2 = 600mA; 0 Phase Shift; PS = Low)
3.62 3.61 3.60 3.59 LX2 4 LX1 2 0 -2 3.61
Input Ripple
(CIN = 2 x 10F; VIN = 3.6V; VOUT1 = 1.8V; VOUT2 = 2.5V; IOUT1,2 = 600mA; 180 Phase Shift)
Input Voltage (top) (V)
Input Voltage (top) (V)
3.60 3.59 LX2
Switching Voltage LX1,LX2 (V)
Switching Voltage LX1,LX2 (V)
4 LX1 2 0 -2
Time (0.2s/div)
Time (0.2s/div)
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AAT2513
Dual 600mA Step-Down Converter with Synchronization Functional Block Diagram
FB1 VCC VIN1
Err. Amp. Voltage Reference
Comp
DH
Logic
LX1
EN1 AGND
Control Logic
DL
PGND1 VIN2
Oscillator
MODE/SYNC PS FB
Comp . DH
Err. Amp.
LX2
Logic
Voltage Reference
EN2
Control Logic
DL
PGND2
Functional Description
The AAT2513 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 or a more efficient light load (LL) mode. 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% at a 1mA load.
Soft Start / Enable
The AAT2513 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 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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AAT2513
Dual 600mA Step-Down Converter with Synchronization
VIN C3 10F
5 10
U1 AAT2513 VIN1 EN1 VCC LX1 FB1 N/C AGND PGND1 VIN2 EN2 PS LX2 FB2 MODE/SYNC N/C PGND2
16 9
1.8V
11
2.5V
1 14 3 12 15 13
L1 2.2uH R1 118k C1 4.7F R2 59.0k
7 4 6 2 8
L2 2.2H R3 187k R4 59.0k C2 4.7F
Figure 1: AAT2513 Typical Schematic.
Low Supply UVLO
Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation.
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 AAT2513 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.
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.
PWM/LL Operation
For fixed frequency, with 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.
m=
0.75 VO 0.75 1.8V A = = 0.6 L 2.2H sec
L=
Clock Phase and Frequency
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.
0.75 VO 0.75V VO s 1.2 A VO = A m 0.6 s s 2.5V = 3.1H A
= 1.2
In this case a standard 3.3H value is selected.
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AAT2513
Dual 600mA Step-Down Converter with Synchronization
Table 1 displays the suggested inductor values for the AAT2513. 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. At full load the inductor DC loss is 35mW which corresponds to a 3.2% loss in efficiency for a 600mA, 1.8V output. 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.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
Because the AAT2513 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. The maximum input capacitor RMS current is:
IRMS = IO1 *
Input Capacitor
A key feature of the AAT2513 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.
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.
IO1(MAX) + IO2(MAX) 2
CIN =
VO V 1- O VIN VIN
VPP - ESR FS IO
IRMS(MAX) =
Configuration
0.6V adjustable with external resistive divider
Output Voltage
0.6V-2.0V 2.5V 3.3V
Inductor
2.2H 3.3H 4.7H
Slope Compensation
0.6A/s
Table 1: Inductor Values. 12
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AAT2513
Dual 600mA Step-Down Converter with Synchronization
This equation also makes the worst-case assumption that both converters are operating at 50% duty cycle synchronized. The term VIN VIN 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.
VO
V * 1- O
should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system.
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 two to three switching cycles and can be estimated by:
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 AAT2513. 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. 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)
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:
VOUT * (VIN(MAX) - VOUT) L * F * VIN(MAX) 2* 3 * 1
IRMS(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.
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Dual 600mA Step-Down Converter with Synchronization
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.
VOUT 1.5V R1 = V -1 * R2 = 0.6V - 1 * 59k = 88.5k REF
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:
PTOTAL =
IO12 * (RDSON(HS) * VO1 + RDSON(LS) * [VIN -VO1]) VIN IO22 * (RDSON(HS) * VO2 + RDSON(LS) * [VIN -VO2]) VIN
+
+ (tsw * F * [IO1 + IO2] + 2 * IQ) * VIN
With an external feedforward capacitor (C4 and C5 of Figure 2) the AAT2513 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
IQ is the AAT2513 quiescent current for one channel and tSW is used to estimate the full load switching losses. For the condition where channel one is in dropout at 100% duty cycle the total device dissipation reduces to:
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
PTOTAL = IO12 * RDSON(HS) IO22 * (RDSON(HS) * VO2 + RDSON(LS) * [VIN -VO2]) VIN
+
+ (tsw * F * IO2 + 2 * IQ) * VIN
Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. 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.
Thermal Calculations
There are three types of losses associated with the AAT2513 converter: switching losses, conduction losses, and quiescent current losses. The conduction
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2513.2007.04.1.1
AAT2513
Dual 600mA Step-Down Converter with Synchronization
PCB Layout
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. 2. 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. 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. 4. 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. 5. For good thermal coupling, PCB vias are required from the pad for the QFN paddle to the ground plane. The via diameter should be 0.3mm to 0.33mm and positioned on a 1.2 mm grid.
2513.2007.04.1.1
15
AAT2513
Dual 600mA Step-Down Converter with Synchronization Design Example
Specifications
VO1 VO2 VIN FS TAMB 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 = 2.2H (see table 1). A A
For Sumida CDRH2D11 2.2H DCR = 98m.
2.5V VO1 VO1 2.5V 1= 1= 230mA L F VIN 3.3H 1.7MHz 4.2V
I1 =
IPK1 = IO1 +
I1 = 0.4A + 0.115A = 0.515A 2
PL1 = IO12 DCR = 0.6A2 123m = 44mW
2.5V VO2 Output Inductor
L1 = 1.2 s s VO1 = 1.2 2.5V = 3.3H (see table 1). A A
For Sumida inductor CDRH2D11 3.3H DCR = 123m.
2.5V VO2 VO2 2.5V 1= 1 = 230mA L F VIN 3.3H 1.7MHz 4.2V
I2 =
IPK2 = IO2 +
I2 = 0.4A + 0.115A = 0.515A 2
PL2 = IO22 DCR = 0.6A2 123m = 44mW
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2513.2007.04.1.1
AAT2513
Dual 600mA Step-Down Converter with Synchronization
1.8V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 4.8F 0.2V * 1.7MHz VDROOP * FS (VOUT) * (VIN(MAX) - VOUT) 1 1.8V * (4.2V - 1.8V) * = 31mArms = L * F * VIN(MAX) 2 * 3 2.2H * 1.7MHz * 4.2V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (31mA)2 = 4.8W
2.5V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 4.8F 0.2V * 1.7MHz VDROOP * FS (VOUT) * (VIN(MAX) - VOUT) 1 2.5V * (4.2V - 2.5V) * = 67mArms = L * F * VIN(MAX) 2 * 3 3.3H * 1.7MHz * 4.2V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (67mA)2 = 22W
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1 1 = = 10F VPP 25mV - ESR * 4 * FS - 5m * 4 * 1.7MHz IO1 + IO2 1.2A
IO1 + IO2 = 0.6Arms 2
IRMS(MAX) =
P = esr * IRMS2 = 5m * (0.6A)2 = 0.8mW
2513.2007.04.1.1
17
AAT2513
Dual 600mA Step-Down Converter with Synchronization
AAT2513 Losses
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
+ (tsw * F * IO2 + 2 * IQ) * VIN
=
0.62 * (0.725 * 2.5V + 0.7 * (2.7V - 2.5V)) + 0.62 * (0.725 * 1.8V + 0.7 * (2.7V - 1.8V))
2.7V
+ (5ns * 1.7MHz * 0.6A + 60A) * 2.7V = 533mW
TJ(MAX) = TAMB + JA * PLOSS = 85C + (50C/W) * 533mW = 111C TJ(MAX) = TAMB + JA * PLOSS = 85C + (28C/W) * 533mW = 100C
Phase Shift
3 2 1
L1, L2 CDRH2D11 C1, C2 4.7F 10V 0805 X5R U1 AAT2513
6 16 1 2 3 4
VIN C4 100pF
VIN
LX2
N/C LX2 PGND2 MODE/SYNC VCC EN1 EN2 PGND1
15
VO2 L2
VIN
N/C VIN2 PS AGND FB2 FB1 VIN1 LX1
14 13 12 11 10 9 8
Sync C7 1F C2
VCC
1 2 3
C5 100pF
R3 88.7k
R1 187k
LX1 C8 0.1F L1 VO1 C6 1F
C10 120F R4 59.0k GND
R2 59.0k
5 7
C9 10F
C3 10F
C1
GND
R5 10
VCC
VIN
321 321
GND
GND GND
Enable 2
Enable 1
Figure 2: AAT2513 Evaluation Board Schematic1.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10F.
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2513.2007.04.1.1
AAT2513
Dual 600mA Step-Down Converter with Synchronization
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, 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
R2, R4 = 221k1 R1, R3 (k)
75.0 113 150 187 221 261 301 332 442 464 523 715 1000
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
Fixed Version VOUT (V)
0.6-3.3V
R2, R4 not used R1, R3 (k)
zero
L1, L2 (H)
2.2
Table 5: Evaluation Board Component Values.
Figure 3: AAT2513 Evaluation Board Top Side.
Figure 4: AAT2513 Evaluation Board Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221k. 2513.2007.04.1.1
19
AAT2513
Dual 600mA Step-Down Converter with Synchronization
Manufacturer
Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden
Part Number
CDRH2D11 CDRH2D11 CDRH2D11 CDRH2D11 CBC2518T CBC2518T CBC2518T CBC2016T
Inductance (H)
1.5 2.2 3.3 4.7 1.0 2.2 4.7 2.2
Max DC Current (A)
1.48 1.27 1.02 0.88 1.2 1.1 0.92 0.83
DCR ()
0.068 0.098 0.123 0.170 0.08 0.13 0.2 0.2
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
Type
Shielded Shielded Shielded Shielded Wire Wound Chip Wire Wound Chip Wire Wound Chip Wire Wound Chip
Table 3: Typical Surface Mount Inductors.
Manufacturer
Murata Murata Murata
Part Number
GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39
Value
4.7F 10F 22F
Voltage
10V 6.3V 6.3V
Temp. Co.
X5R X5R X5R
Case
0805 0805 0805
Table 4: Surface Mount Capacitors.
20
2513.2007.04.1.1
AAT2513
Dual 600mA Step-Down Converter with Synchronization Ordering Information
Voltage Package
QFN33-16
Channel 1 Channel 2
Marking1
UFXYY
Part Number (Tape and Reel)2
AAT2513IVN-AA-T1
0.6V
0.6V
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/pbfree.
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. 2513.2007.04.1.1
21
AAT2513
Dual 600mA Step-Down Converter with Synchronization Package Information1
QFN33-16
Pin 1 Identification
1
0.230 0.05
5
3.000 0.05
C0.3
0.400 0.100
Pin 1 Dot By Marking
13 9
3.000 0.05
0.500 0.05
Top View
Bottom View
1.70 0.05
0.214 0.036
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.
(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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611 22
2513.2007.04.1.1
0.900 0.100

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