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PRODUCT DATASHEET
AAT2515
SystemPowerTM
General Description
The AAT2515 is a dual channel synchronous buck converter operating with an input voltage range of 2.7V to 5.5V, making it ideal for applications with single-cell lithium-ion/polymer batteries. Both regulators have independent input and enable pins. Offered with fixed or adjustable output voltages, each channel is designed to operate with 27A (typical) of quiescent current, allowing for high efficiency under light load conditions. The AAT2515 requires only three external components (CIN, COUT, and LX) for each converter, minimizing cost and real estate. Both channels are designed to deliver 600mA of load current and operate with a switching frequency of 1.4MHz, reducing the size of external components. The AAT2515 is available in a Pb-free, 12-pin TDFN33 package and is rated over the -40C to +85C temperature range.
Dual 600mA Fast Transient High Frequency Buck Converter
Features
* VIN Range: 2.7V to 5.5V * Output Current: Channel 1: 600mA Channel 2: 600mA * 98% Efficient Step-Down Converter * Integrated Power Switches * 100% Duty Cycle * 1.4MHz Switching Frequency * Internal Soft Start * 150s Typical Turn-On Time * Over-Temperature Protection * Current Limit Protection * TDFN33-12 Package * -40C to +85C Temperature Range
Applications
* * * * * Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers
Typical Application
V OUT1 VIN1 LX1 L1 4.7H
V BAT
C IN 10F
VIN2
FB1
AAT2515
EN1 LX2 L2 4.7H EN2 GND FB2
VOUT2
COUT 10F 10F
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
Pin Descriptions
Pin #
1 2 3, 6, 7, 10 4 5 8 9 11 12
Dual 600mA Fast Transient High Frequency Buck Converter
Symbol
EN1 FB1 GND EN2 FB2 LX2 VIN2 LX1 VIN1
Function
Enable pin for Channel 1. Active high. When connected low, it disables the channel and consumes less than 1A of current. Feedback input pin for Channel 1. This pin is connected to the converter output. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Ground. Enable pin for Channel 2. Active high. When connected low, it disables the channel and consumes less than 1A of current. Feedback input pin for Channel 2. This pin is connected to the converter output. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Power switching node for Channel 2. Output switching node that connects to the output inductor. Input supply voltage for Channel 2. Must be closely decoupled. Power switching node for Channel 2. Output switching node that connects to the output inductor. Input supply voltage for Channel 1. Must be closely decoupled.
Pin Configuration
TDFN33-12 (Top View)
EN1 FB1 GND EN2 FB2 GND
1 2 3 4 5 6
12 11 10 9 8 7
VIN1 LX1 GND VIN2 LX2 GND
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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
Absolute Maximum Ratings1
Symbol
VIN VLX VFB VEN TJ TLEAD
Description
Input Voltages to GND LX to GND FB1 and FB2 to GND EN1 and EN2 to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to 150 300
Units
V V V V C C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation Thermal Resistance2
Value
2.0 50
Units
W C/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. 2. Mounted on an FR4 board.
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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
Electrical Characteristics1
VIN = 3.6V; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol
VIN VOUT VOUT IQ ISHDN ILX_LEAK IFB ILIM RDS(ON)H RDS(ON)L VLINE FOSC TS TSD THYS VEN(L) VEN(H) IEN
Description
Input Voltage Output Voltage Tolerance Output Voltage Range Quiescent Current Shutdown Current LX Leakage Current Feedback Leakage P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance Line Regulation Oscillator Frequency Start-Up Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current
Conditions
IOUT = 0 to 600mA; VIN = 2.7V to 5.5V Per Channel EN1 = EN2 = GND VIN = 5.5V, VLX = 0 to VIN VFB = 1.0V Both Channels
Min
2.7 -3.0 0.6
Typ
Max
5.5 3.0 VIN 70 1.0 1.0 0.2
Units
V % V A A A A A % MHz s C C V V A
27
VIN = 2.7V to 5.5V From Enable to Output Regulation; Both Channels
1.2 0.45 0.40 0.2 1.4 150 140 15 0.6 1.4 -1.0
VIN = VFB = 5.5V
1.0
1. The AAT2515 is 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
AAT2515
SystemPowerTM
Typical Characteristics
EN1 = VIN; EN2 = GND.
Dual 600mA Fast Transient High Frequency Buck Converter
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7H)
100 90 1.0
DC Regulation
(VOUT = 1.8V)
VIN = 2.7V Output Error (%)
0.5
Efficiency (%)
80 70 60 50 0.1
VIN = 3.6V
VIN = 4.2V
VIN = 4.2V
0.0
-0.5
VIN = 3.6V VIN = 2.7V
1 10 100 1000
1
10
100
1000
-1.0 0.1
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 6.8H)
100 90
DC Regulation
(VOUT = 2.5V)
1.0
VIN = 2.7V Output Error (%) VIN = 5.0V VIN = 4.2V VIN = 3.6V
VIN = 4.2V
0.5
Efficiency (%)
VIN = 5.0V
80 70 60 50 0.1
0.0
-0.5
VIN = 3.6V VIN = 3.0V
1
10
100
1000
-1.0
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8H)
100 90
DC Regulation
(VOUT = 3.3V; L = 6.8H)
1.0
VIN = 3.6V Output Error (%) VIN = 4.2V VIN = 5.0V
VIN = 5.0V
0.5
Efficiency (%)
80 70 60 50 0.1
VIN = 4.2V
0.0
-0.5
VIN = 3.6V
1
10
100
1000
-1.0
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
Typical Characteristics
EN1 = VIN; EN2 = GND.
Dual 600mA Fast Transient High Frequency Buck Converter
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) Enable and Output Voltage (top) (V)
5.0 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0 -5.0 1.6 1.4 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 1.2 0.40 0.30
Line Regulation
(VOUT = 1.8V)
VEN
VO
Accuracy (%)
0.20 0.10 0.00 -0.10 -0.20 -0.30 -0.40 2.5 3.0 3.5
IOUT = 10mA
Inductor Current (bottom) (A)
IOUT = 1mA
IL
IOUT = 400mA
4.0
4.5
5.0
5.5
6.0
Time (100s/div)
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 400mA)
2.0 15.0 12.0 9.0
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
Output Error (%)
Variation (%)
1.0
6.0 3.0 0.0 -3.0 -6.0 -9.0 -12.0 -15.0 -40
0.0
-1.0
-2.0 -40
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
Frequency vs. Input Voltage
2.0
No Load Quiescent Current vs. Input Voltage
50
Frequency Variation (%)
Supply Current (A)
1.0 0.0 -1.0 -2.0 -3.0 -4.0
VOUT = 1.8V
45 40 35 30 25 20 15 10
85C
25C
VOUT = 2.5V
VOUT = 3.3V
-40C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
Typical Characteristics
EN1 = VIN; EN2 = GND.
Dual 600mA Fast Transient High Frequency Buck Converter
P-Channel RDS(ON) vs. Input Voltage
750 700 650 750 700 650
N-Channel RDS(ON) vs. Input Voltage
RDS(ON) (m)
RDS(ON) (m)
120C
100C
120C
600 550 500 450 400 350 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25C 85C
600 550 500 450 400 350 300 2.5 3.0 3.5 25C 85C
100C
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Load Transient Response
(1mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10F; CFF = 100pF)
2.0 1.9 1.90 1.85 1.80 1.75
Load Transient Response
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7F) Load and Inductor Current (200mA/div) (bottom) Load and Inductor Current (200mA/div) (bottom) VO IO
400mA 300mA 0.4
VO IO IL
Output Voltage (top) (V)
1.7
300mA 1mA
Output Voltage (top) (V)
1.8
0
IL Time (50s/div)
0.3 0.2 0.1
Time (50s/div)
Load Transient Response
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10F)
1.90 1.85 1.80 1.75
Load Transient Response
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10F; C4 = 100pF)
1.850 1.825 1.800 1.775
Load and Inductor Current (200mA/div) (bottom)
Load and Inductor Current (200mA/div) (bottom)
VO IO
400mA 300mA
0.4
VO IO
Output Voltage (top) (V)
Output Voltage (top) (V)
400mA 300mA 0.4
IL Time (50s/div)
0.3 0.2 0.1
IL Time (50s/div)
0.3 0.2 0.1
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
Typical Characteristics
EN1 = VIN; EN2 = GND.
Dual 600mA Fast Transient High Frequency Buck Converter
Line Response
(VOUT = 1.8V @ 400mA) Output Voltage (AC coupled) (top) (mV)
1.82 1.81 6.0 5.5 40 20 0 -20 -40 -60 -80 -100 -120
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
0.30
VO
0.25
Inductor Current (bottom) (A)
Output Voltage (top) (V)
0.20 0.15 0.10
Input Voltage (bottom) (V)
1.80 1.79 1.78 1.77 1.76
5.0 4.5 4.0 3.5 3.0
IL
0.05 0.00 -0.05 -0.10
Time (25s/div)
Time (10s/div)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) Output Voltage (AC coupled) (top) (mV)
40 20 0 -20 -40 -60 -80 -100 -120 0.9
VO
0.8
Inductor Current (bottom) (A)
0.7 0.6 0.5 0.4 0.3
IL Time (500ns/div)
0.2 0.1
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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
Functional Block Diagram
FB1 VIN1
Err. Amp.
Comp.
DH
Logic
Voltage Reference
LX1
DL
EN1
Control Logic
GND
GND
See Note
VIN2
FB2
Err. Amp.
Comp.
DH
LX2
Logic
DL
Voltage Reference
EN2
See Note
Control Logic
GND
GND
Note: Internal resistor divider included for fixed output voltage versions. For low voltage versions, the feedback pin is tied directly to the error amplifier input.
Functional Description
The AAT2515 is a high performance power management IC comprised of two buck converters. Each channel has independent input voltages and enable pins. Designed to operate at 1.4MHz of switching frequency, the converters require only three external components (CIN, COUT, and LX), minimizing cost and size of external components. Both converters are designed to operate with an input voltage range of 2.7V to 5.5V. Typical values of the output filter are 4.7H and 10F ceramic capacitor. The output voltage operates to as low as 0.6V and is offered as both fixed and adjustable. Power devices are sized for 600mA current capability while maintaining over 90% efficiency at full load. Light load efficiency is maintained at greater than 80% down to 500A of load current. Both channels have excellent transient response, load, and line regulation. Transient response time is typically less than 20s.
The AAT2515 also features soft-start control to limit inrush current. Soft start increases the inductor current limit point in discrete steps when power is applied to the input or when the enable pins are pulled high. It limits the current surge seen at the input and eliminates output voltage overshoot. The enable input, when pulled low, forces the converter into a low power, non-switching state consuming less than 1A of current. For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140C with 15C of hysteresis. The under-voltage lockout guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation.
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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
Input Capacitor
Select a 4.7F to 10F X7R or X5R ceramic capacitor for the input. 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.
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 AAT2515 is 0.24A/s. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7H inductor.
CIN =
V VO 1- O VIN VIN
VPP - ESR FS IO
m=
0.75 VO 0.75 1.5V A = = 0.24 L 4.7H s
This equation provides an estimate for the input capacitor required for a single channel. Configuration
0.6V Adjustable With External Feedback Fixed Output
Output Voltage
1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V 0.6V to 3.3V
Inductor
2.2H 4.7H 6.8H 4.7H
This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed version. When externally programming the 0.6V version to a 2.5V output, the calculated inductance would be 7.5H.
Table 1: Inductor Values.
0.75V 0.75 VO s 3 A VO L= = m 0.24A /s =3 s 2.5V = 7.5H A
The equation below solves for input capacitor size for both channels. It makes the worst-case assumptions that both converters are operating at 50% duty cycle and are synchronized.
In this case, a standard 6.8H value is selected. For highvoltage fixed versions (2.5V and above), m = 0.48A/s. Table 1 displays inductor values for the AAT2515 fixed and adjustable options. 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 saturation characteristics. The inductor should not show any appreciable saturation under 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 4.7H CDRH3D16 series inductor selected from Sumida has a 105m DCR and a 900mA DC current rating. At full load, the inductor DC loss is 37.8mW which gives a 4.2% loss in efficiency for a 600mA 1.5V output.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
Because the AAT2515 channels will generally operate at different duty cycles and are not synchronized, the actual ripple will vary and be less than the ripple (VPP) used to solve for the input capacitor in the equation above. 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 *
VO1 V * 1 - O1 + IO2 * VIN VIN
VO2 V * 1 - O2 VIN VIN
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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
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 affect converter performance, a high ESR tantalum or aluminum electrolytic capacitor should be placed in parallel with the low ESR, ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. 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
This equation also makes the worst-case assumption that both converters are operating at 50% duty cycle and are synchronized. Since the converters are not synchronized and are not both operating at 50% duty cycle, the actual RMS current will always be less than this. Losses associated with the input ceramic capacitor are typically minimal. The term V V appears in both the input voltage ripple and input capacitor RMS current equations. It is a 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
Output Capacitor
The output capacitor limits the output ripple and provides holdup during large load transitions. A 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:
VO
V * 1- O
The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2515. Low ESR/ ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize the stray inductance, the capacitor 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 (C3 and C8) can be seen in the evaluation board layout in Figure 2. Since decoupling must be as close to the input pins as possible, it is necessary to use two decoupling capacitors. C3 provides the bulk capacitance required for both converters, while C8 is a high frequency bypass capacitor for the second channel (see C3 and C8 placement in Figure 2). 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 affect 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
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 10F. 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
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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PRODUCT DATASHEET
AAT2515
SystemPowerTM Dual 600mA Fast Transient High Frequency Buck Converter
Thermal Calculations
There are three types of losses associated with the AAT2515 converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. 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:
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage, the 0.6V version can be programmed externally. Resistors R1 through R4 of Table 2 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
The adjustable version of the AAT2515 in combination with an external feedforward capacitor (C4 and C5 of Figure 1) 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 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
+
+ (tsw * F * [IO1 + IO2] + 2 * IQ) * VIN
IQ is the AAT2515 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:
R2, R4 = 221k R1, R3
75K 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M
R1, R3 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267
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 TDFN33-12 package which is 50C/W.
Table 2: Adjustable Resistor Values For Use With 0.6V Version.
TJ(MAX) = PTOTAL * JA + TAMB
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
PCB Layout
The following guidelines should be used 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 large input capacitor C3 should connect as closely as possible to VIN and GND, as shown in Figure 2. The additional input bypass capacitor C8 is necessary for proper high frequency decoupling of the second converter. 2. The output capacitor and inductor should be connected as closely as possible. The connection of the inductor to the LX pin should also be as short as possible.
Dual 600mA Fast Transient High Frequency Buck Converter
3. The feedback trace should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. If external feedback resistors are used, they should be placed as closely as possible to the FB pin. This prevents noise from being coupled into the high impedance feedback node. The resistance of the trace from the load return to GND should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. For good thermal coupling, PCB vias are required from the pad for the TDFN paddle to the ground plane. The via diameter should be 0.3mm to 0.33mm and positioned on a 1.2 mm grid.
4.
5.
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
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) 1.4 MHz 85C
Dual 600mA Fast Transient High Frequency Buck Converter
2.5V VO1 Output Inductor
s s L1 = 3 A VO1 = 3 A 2.5V = 7.5H (see Table 1)
For Sumida inductor CDRH3D16, 10H, DCR = 210m.
I1 =
2.5V VO1 V 2.5V 1 - O1 = 1= 72.3mA L1 F VIN 10H 1.4MHz 4.2V
IPK1 = IO1 +
I1 = 0.6A + 0.036A = 0.64A 2
PL1 = IO12 DCR = 0.6A2 210m = 75.6mW
1.8V VO2 Output Inductor
s s L2 = 3 A VO2 = 3 A 1.8V = 5.4H (see Table 1)
For Sumida inductor CDRH3D16, 4.7H, DCR = 105m.
I2 =
1.8V VO2 V 1.8V 1 - O2 = 1= 156mA LF VIN 4.7H 1.4MHz 4.2V
IPK2 = IO2 +
I2 = 0.6A + 0.078A = 0.68A 2
PL2 = IO22 DCR = 0.6A2 105m = 37.8mW
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
2.5V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 6.4F; use 10F VDROOP * FS 0.1V * 1.4MHz 1 2* 3 * (VOUT) * (VIN(MAX) - VOUT) 1 2.5V * (4.2V - 2.5V) * = 21mArms = L * F * VIN(MAX) 2 * 3 10H * 1.4MHz * 4.2V
Dual 600mA Fast Transient High Frequency Buck Converter
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (21mA)2 = 2.2W
1.8V Output Capacitor
COUT = 3 * ILOAD 3 * 0.3A = = 6.4F; use 10F VDROOP * FS 0.1V * 1.4MHz (VOUT) * (VIN(MAX) - VOUT) 1 1.8V * (4.2V - 1.8V) * = 45mArms = L * F * VIN(MAX) 2 * 3 4.7H * 1.4MHz * 4.2V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (45mA)2 = 10W
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
=
1 = 11.3F; use 10F 25mV - 5m * 4 * 1.4MHz 1.2A
IRMS(MAX) =
IO1 + IO2 = 0.6Arms 2
P = esr * IRMS2 = 5m * (0.6A)2 = 1.8mW
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15
PRODUCT DATASHEET
AAT2515
SystemPowerTM
AAT2515 Losses
The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an ambient temperature of 85C and a junction temperature of 120C.
Dual 600mA Fast Transient High Frequency Buck Converter
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 * 1.4MHz * 0.6A + 60A) * 2.7V = 530mW TJ(MAX) = TAMB + JA * PLOSS = 85C + (50C/W) * 530mW = 111C
Output 1 Enable VIN
123
C41
R1 see Table 3
U1 AAT2515
1 2 3
LX1
12 11
EN1 FB1 GND EN2 FB2 GND
VIN1 LX1 GND VIN2 LX2 GND
L1 see Table 3 C3 VO1 LX2 VO2 C11 10F C7 0.01F C21 10F GND
10 9 8 7
C51
R3 see Table 3
4 5 6
10F
L2 see Table 3 C6 0.01F
R4 59.0k GND
R2 59.0k
C8 0.1F
321
Output 2 Enable
Figure 1: AAT2515 Evaluation Board Schematic.
1. For enhanced transient configuration C5, C4 = 100pF.
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PRODUCT DATASHEET
AAT2515
SystemPowerTM
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
Dual 600mA Fast Transient High Frequency Buck Converter
R2, R4 = 59k R1, R3 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267
R2, R4 = 221k1 R1, R3 (k)
75.0 113 150 187 221 261 301 332 442 464 523 715 1000
L1, L2 (H)
2.2 2.2 2.2 2.2 2.2 2.2 4.7 4.7 4.7 4.7 6.8 6.8 6.8
Fixed Version VOUT (V)
0.6-3.3V
R2, R4 Not Used R1, R3 (k)
0
L1, L2 (H)
4.7
Table 3: Evaluation Board Component Values.
Figure 2: AAT2515 Evaluation Board Top Side.
Figure 3: AAT2515 Evaluation Board Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221k.
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17
PRODUCT DATASHEET
AAT2515
SystemPowerTM
Manufacturer
Sumida Sumida Sumida Murata Murata Coilcraft Coiltronics Coiltronics Coiltronics
Dual 600mA Fast Transient High Frequency Buck Converter
Part Number Inductance (H)
2.2 4.7 6.8 4.7 4.7 4.7 4.7 6.8 4.7
Max DC Current (A)
1.20 0.90 0.73 0.40 0.45 0.80 0.98 0.82 1.30
DCR ()
0.072 0.105 0.170 0.80 0.20 0.27 0.122 0.175 0.122
Size (mm) LxWxH
3.8x3.8x1.8 3.8x3.8x1.8 3.8x3.8x1.8 2.0x1.6x0.95 2.5x3.2x2.0 3.2x3.2x1.0 3.1x3.1x1.85 3.1x3.1x1.85 5.7x4.4x1.0
Type
Shielded Shielded Shielded Non-Shielded Non-Shielded 1mm Shielded Shielded 1mm Shielded
CDRH3D16-2R2 CDRH3D16-4R7 CDRH3D16-6R8 LQH2MCN4R7M02 LQH32CN4R7M23 LPO3310-472 SD3118-4R7 SD3118-6R8 SDRC10-4R7
Table 4: Typical Surface Mount Inductors. Manufacturer
Murata Murata Murata
Part Number
GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39
Value
4.7F 10uF 22uF
Temp. Co.
X5R X5R X5R
Case
0805 0805 0805
Table 5: Surface Mount Capacitors.
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2515.2007.12.1.0
PRODUCT DATASHEET
AAT2515
SystemPowerTM
Ordering Information
Voltage Package
TDFN33-12 Channel 1 0.6V Channel 2 0.6V
Dual 600mA Fast Transient High Frequency Buck Converter
Marking1
2XXYY
Part Number (Tape and Reel)2
AAT2515IWP-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/pbfree.
Legend Voltage
Adjustable (0.6V) 0.9 1.2 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3 4.2
Code
A B E G I Y N O P Q R S T W C
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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19
PRODUCT DATASHEET
AAT2515
SystemPowerTM
Package Information
TDFN33-12
Index Area Detail "A" 0.43 0.05
Dual 600mA Fast Transient High Frequency Buck Converter
3.00 0.05
2.40 0.05
0.1 REF C0.3 0.45 0.05
Pin 1 Indicator (optional)
3.00 0.05
1.70 0.05
Top View
Bottom View Detail "A"
0.75 0.05
0.05 0.05
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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0.23 0.05
0.23 0.05
2515.2007.12.1.0

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