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Dual 600mA, 1MHz Step-Down DC/DC Converter General Description
The AAT2511 is a member of AnalogicTech's Total Power Management ICTM (TPMICTM) product family. It is comprised of two 1MHz step-down converters designed to minimize external component size and cost. The input voltage ranges from 2.7V to 5.5V. The output voltage ranges from 0.6V to the maximum applied input voltage and is externally adjustable. Peak current mode control with internal compensation provides a stable converter with low ESR ceramic output capacitors for extremely low output ripple. Each channel has a low 25A quiescent operating current, which is critical for maintaining high efficiency at light load. For maximum battery life, each converter's highside P-channel MOSFET conducts continuously when the input voltage approaches dropout (100% duty cycle operation). Both regulators have independent input and enable inputs. The AAT2511 is available in a Pb-free, thermallyenhanced 12-pin TDFN33 package, and is rated over the -40C to +85C temperature range.
AAT2511
Features
* * * * * * * * * * * * * * * * *
SystemPowerTM
Up to 97% Efficiency 25A Quiescent Current Per Channel VIN Range: 2.7V to 5.5V VOUT Range: 0.6V to VIN Output Current: 600mA Low RDS(ON) 0.4 Integrated Power Switches Low Drop Out 100% Duty Cycle 1.0MHz Switching Frequency Shutdown Current <1A Current Mode Operation Internal Reference Soft Start Short-Circuit Protection Fast Turn-On (100s Typical) Over-Temperature Protection 3mm x 3mm, < 1mm high TDFN33-12 Package -40C to +85C Temperature Range
Applications
* * * * * * Cellular Phones Digital Cameras Handheld Instruments Microprocessor/DSP Core/IO Power PDAs and Handheld Computers Portable Media Players
Typical Application
AAT2511 Efficiency
(VIN = 3.3V)
VIN C3 10F
12
100
U1 AAT2511
VIN1 EN1 LX1 FB1 SGND1 GND1 VIN2 EN2 LX2 FB2 SGND2 GND2
9 4 8 5 6 7 1
C8 0.1F 2.5V L2 10H R3 187k
95
1.8V L1 4.7H R1 118k
11 2 3
Efficiency (%)
90 85 80 75 70 65 60 0.1 1 10 100 1000
2.5V 1.8V
C1 10F
R2 59.0k
10
R4 59.0k
C2 10F
Load Current (mA)
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Dual 600mA, 1MHz Step-Down DC/DC Converter Pin Descriptions
Pin #
1, 4
AAT2511
Symbol
EN1, EN2
Function
Converter enable input. 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 the source voltage (VIN1, VIN2). Feedback input pin. An external resistive divider ties to this point and programs the output voltage to the desired value. Signal ground. Return the feedback resistive divider to this ground. See section on PCB layout guidelines and evaluation board layout diagram. Main power ground return. Connect to the input and output capacitor return. See section on PCB layout guidelines and evaluation board layout diagram. Output switching node that connects to the respective output inductor. Input supply voltage. Must be closely decoupled to the respective power gnd. Exposed paddle (bottom). Use properly sized vias for thermal coupling to the ground plane. See section on PCB layout guidelines.
2, 5 3, 6 7, 10 8, 11 9, 12 EP
FB1, FB2 SGND1, SGND2 GND2, GND1 LX2, LX1 VIN2, VIN1
Pin Configuration
TDFN33-12 (Top View)
EN1 FB1 SGND1 EN2 FB2 SGND2
1 2 3 4 5 6
12 11 10 9 8 7
VIN1 LX1 GND1 VIN2 LX2 GND2
2
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Dual 600mA, 1MHz Step-Down DC/DC Converter Absolute Maximum Ratings1
Symbol
VIN VLX VFB VEN TJ TLEAD
AAT2511
Description
VIN1, VIN2 to SGND1, SGND2, GND1, and GND2 LX1, LX2 to GND1, GND2 FB1 and FB2 to SGND1, SGND2, GND1, and GND2 EN1 and EN2 to SGND1, SGND2, GND1, and GND2 Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0 -0.3 to VP + 0.3 -0.3 to VP + 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 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 with exposed paddle connected to ground plane. 2511.2006.05.1.4
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Dual 600mA, 1MHz Step-Down DC/DC Converter Electrical Characteristics1
TA = -40C to 85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.6V. Symbol
VIN VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLK VLinereg VFB TS FOSC TSD THYS
EN
AAT2511
Description
Input Voltage UVLO Threshold Output Voltage Tolerance Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance LX Leakage Current Line Regulation FB Threshold Voltage Accuracy Start-Up Time Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current
Conditions
Min
2.7
Typ
Max
5.5 2.6
Units
V V mV V % V A A mA A %/V mV s MHz C C
Step-Down Converter Channels
VIN Rising Hysteresis VIN Falling IOUT = 0 to 400mA, VIN = 2.7 - 5.5V No Load, 0.6V Adjustable Version, Per Channel EN = SGND = GND
100 1.8 -3.0 0.6 25 600 0.45 0.4 +3.0 VIN 50 1.0
VIN = 5.5V, VLX = 0 to VIN, EN = SGND = GND VIN = 2.7V to 5.5V 0.6V Output, No Load, TA = 25C From Enable to Output Regulation TA = 25C
1 591 0.7 600 100 1.0 140 15 0.6 0.2 609 1.5
VEN(L) VEN(H) IEN
VIN = VFB = 5.5V
1.4 -1.0
1.0
V V A
1. The AAT2511 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. 2. For adjustable version with higher than 2.5V output, please consult your AnalogicTech representative.
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Dual 600mA, 1MHz Step-Down DC/DC Converter Typical Channel Characteristics
Efficiency vs. Load
(VOUT = 3.3V; L = 10H)
100 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0
AAT2511
(VOUT = 3.3V; L = 10H)
DC Regulation
Efficiency (%)
90
VIN = 3.9V VIN = 4.2V
80
Output Error (%)
VIN = 4.2V
70
VIN = 3.9V
60 0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 10H)
100
(VOUT = 2.5V; L = 10H)
3.0
DC Regulation
VIN = 3.3V
Efficiency (%)
90
Output Error (%)
2.0 1.0 0.0 -1.0 -2.0 -3.0 0.1
VIN = 3.3V VIN = 3.6V
VIN = 3.0V
80
VIN = 3.6V
VIN = 3.0V
70
60
0.1
1
10
100
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.5V; L = 4.7H) VIN = 3.6V
Output Error (%)
100 90 3.0
(VOUT = 1.5V; L = 4.7H)
DC Regulation
VIN = 2.7V
2.0 1.0 0.0 -1.0 -2.0 -3.0
VIN = 4.2V VIN = 3.6V
Efficiency (%)
80 70 60 50
VIN = 4.2V
VIN = 2.7V
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
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Dual 600mA, 1MHz Step-Down DC/DC Converter Typical Channel Characteristics
Frequency vs. Input Voltage
(VOUT = 1.8V)
1.0 2.0 1.5
AAT2511
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 2.5V)
Frequency Variation (%)
Output Error (%)
0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -40 -20 0 20 40 60 80 100
Input Voltage (V)
Temperature (C)
Switching Frequency vs. Temperature
(VIN = 3.6V; VO = 1.5V)
0.20 35
Quiescent Current vs. Input Voltage
(VO = 1.8V) 85C
30
Variation (%)
0.10
Supply Current (A)
25C
25
0.00
-0.10
20
-0.20 -40
15 -20 0 20 40 60 80 100 2.5
-40C
3.0 3.5 4.0 4.5 5.0 5.5 6.0
Temperature (C)
Input Voltage (V)
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)
6
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Dual 600mA, 1MHz Step-Down DC/DC Converter Typical Channel Characteristics
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22F)
1.65 1.60 1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00
AAT2511
(30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22F)
2.65 2.55
Load Transient Response
Load and Inductor Current (200mA/div) (bottom)
Load and Inductor Current (200mA/div) (bottom)
1.5 1.3 300mA 30mA 1.1 0.9 0.7 0.5 0.3 0.1 -0.1
1.5 1.3 300mA 30mA 1.1 0.9 0.7 0.5 0.3 0.1 -0.1
Output Voltage (top) (V)
Output Voltage (top) (V)
2.45 2.35 2.25 2.15 2.05
Time (25s/div)
Time (25s/div)
Line Transient
(VOUT = 2.5V @ 500mA)
2.60 2.55 2.50 2.45 2.40 2.35 2.30 2.25 2.20 2.15 7.0 6.5
2 1.5
Line Regulation
(VOUT = 1.5V)
Output Voltage (top) (V)
Accuracy (%)
6.0 5.5 5.0 4.5 4.0 3.5 3.0
Input Voltage (bottom) (V)
1 0.5 0 -0.5 -1 2.5 3
IOUT = 600mA IOUT = 100mA IOUT = 10mA
Time (25s/div)
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; 400mA)
(VIN = 3.6V; VOUT = 1.5V; L = 4.7H)
Soft Start
Output Voltage (AC Coupled) (top) (mV)
20 0 -20 -40 -60 -80 -100 -120
0.8
Enable and Output Voltage (top) (V)
40
0.9
4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0
3.5 3.0
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
0.7 0.6 0.5 0.4 0.3 0.2 0.1
2.5 2.0 1.5 1.0 0.5 0.0 -0.5
Time (250ns/div)
Time (50s/div)
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Dual 600mA, 1MHz Step-Down DC/DC Converter Functional Block Diagram
FB1 VIN1
AAT2511
Err. Amp.
Comp.
DH
Logic
Voltage Reference Control Logic
LX1
DL
EN1
GND1
SGND1 FB2
See Note
VIN2
Err. Amp.
Comp.
DH
Logic
Voltage Reference
LX2
DL
EN2
See Note
Control Logic
GND2
SGND2
Note: Internal resistor divider included for 1.2V versions. For low voltage versions, the feedback pin is tied directly to the error amplifier input.
Operation
Device Summary
The AAT2511 is a constant frequency peak current mode PWM converter with internal compensation. Each channel has independent input, enable, feedback, and ground pins with non-synchronized 1MHz clocks.
Both converters are designed to operate with an input voltage range of 2.7V to 5.5V. The output voltage ranges from 0.6V to the input voltage. The 0.6V fixed model shown in Figure 1 is also the adjustable version and is externally programmable with a resistive divider as shown in Figure 2. The converter MOSFET power stage is sized for 600mA load capability with up to 97% efficiency. Light load efficiency exceeds 80% at a 500A load.
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Dual 600mA, 1MHz Step-Down DC/DC Converter
VIN C3 10F
12
AAT2511
U1 AAT2511
VIN1 EN1 LX1 FB1 SGND1 GND1 VIN2 EN2 LX2 FB2 SGND2 GND2
9 4 8 5 6 7 1
C8 0.1F 2.5V L2 10H C5 100pF R3 187k C2 10F
1.8V L1 C4 100pF R1 118k 4.7H
11 2 3 10
C1 10F
R2 59.0k
R4 59.0k
Figure 1: AAT2511 Adjustable Output with Enhanced Transient Response.
Soft Start
The AAT2511 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.
MOSFET is turned on 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 RDS(ON).
Low Supply
The under-voltage lockout (UVLO) feature guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation.
Low Dropout Operation
For conditions where the input voltage drops to the output voltage level, the converter duty cycle increases to 100%. As 100% duty cycle is approached, the minimum off-time initially forces the high side on-time to exceed the 1MHz clock cycle and reduce the effective switching frequency. Once the input drops below the level where the output can be regulated, the high side P-channel
Fault Protection
For overload conditions, the peak inductor current is limited. Thermal protection disables switching when the internal dissipation or ambient temperature becomes excessive. The junction over-temperature threshold is 140C with 15C of hysteresis.
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Dual 600mA, 1MHz Step-Down DC/DC Converter 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 AAT2511 is 0.24A/sec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7H inductor.
AAT2511
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 38mW for a 600mA 1.5V output.
m=
0.75 VO 0.75 1.5V A = = 0.24 L 4.7H sec
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.
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.
L=
0.75V 0.75 VO sec 3 A VO = m 0.24A /sec sec 2.5V = 7.5H A
CIN =
V VO 1- O VIN VIN
VPP - ESR FS IO
=3
In this case, a standard 10H value is selected.
This equation provides an estimate for the input capacitor required for a single channel.
Configuration
0.6V Adjustable With External Resistive Divider
Output Voltage
0.6V to 2.0V 2.5V
Inductor
4.7H 10H
Slope Compensation
0.24A/sec 0.24A/sec
Table 1: Inductor Values.
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Dual 600mA, 1MHz Step-Down DC/DC Converter
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.
AAT2511
capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2511. 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 4. 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 4). 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 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.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
Because the AAT2511 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
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 VIN * 1 - VIN 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
VO
VO
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 stabi-
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Dual 600mA, 1MHz Step-Down DC/DC Converter
lize 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:
AAT2511
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage, the 0.6V version can be programmed externally. 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
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:
* (VIN(MAX) - VOUT) V IRMS(MAX) = * OUT L * F * VIN(MAX) 2* 3 1
The adjustable version of the AAT2511 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
R2, R4 = 221k R1, R3 (k)
75 113 150 187 221 261 301 332 442 464 523 715
R1, R3 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187
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.
Table 2: Adjustable Resistor Values For Use With 0.6V Version.
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Dual 600mA, 1MHz Step-Down DC/DC Converter
Thermal Calculations
There are three types of losses associated with the AAT2511 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:
AAT2511
Given the total losses, the maximum junction temperature can be derived from the JA for the TDFN33-12 package which is 50C/W.
TJ(MAX) = PTOTAL * JA + TAMB
PCB Layout
The following guidelines should be used to insure a proper layout.
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
IQ is the AAT2511 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:
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.
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 VP and GND, as shown in Figure 3. 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. 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. 4. 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. 5. 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.
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Dual 600mA, 1MHz Step-Down DC/DC Converter Design Example
Specifications
VO1 = 2.5V @ 600mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA VO2 = 1.8V @ 600mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA VIN FS = 2.7V to 4.2V (3.6V nominal) = 1.0 MHz
AAT2511
TAMB = 85C
2.5V VO1 Output Inductor
L1 = 3 sec sec VO1 = 3 2.5V = 7.5H A A
(see Table 1)
For Sumida inductor CDRH3D16, 10H, DCR = 210m.
2.5V VO V 2.5V 1 - O1 = 1 = 100mA VIN 10H 1.0MHz 4.2V L1 F
I1 =
IPK1 = IO1 +
I1 = 0.6A + 0.05A = 0.65A 2
PL1 = IO12 DCR = (0.4A)2 210m = 76mW
1.8V VO2 Output Inductor
L2 = 3 sec sec VO2 = 3 1.8V = 5.4H (see Table 1) A A
For Sumida inductor CDRH3D16, 4.7H, DCR = 105m.
1.8V VO2 V 1.8V 1 - O2 = 1= 218mA VIN 4.7H 1.0MHz 4.2V LF
I2 =
IPK2 = IO2 +
I2 = 0.6A + 0.11A = 0.71A 2
PL2 = IO22 DCR = (0.6A)2 105m = 38mW
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Dual 600mA, 1MHz Step-Down DC/DC Converter
2.5V Output Capacitor
COUT = 3 * ILOAD 3 * 0.6A = = 9F 0.2V * 1MHz VDROOP * FS (VOUT) * (VIN(MAX) - VOUT) 1 2.5V * (4.2V - 2.5V) * = 29mArms = L * F * VIN(MAX) 2 * 3 10H * 1MHz * 4.2V 2* 3 1 *
AAT2511
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (29mA)2 = 4.2W
1.8V Output Capacitor
COUT = 3 * ILOAD 3 * 0.6A = = 9F 0.2V * 1MHz VDROOP * FS (VOUT) * (VIN(MAX) - VOUT) 1 1.8V * (4.2V - 1.8V) * = 63mArms = L * F * VIN(MAX) 2 * 3 4.7H * 1.0MHz * 4.2V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (63mA)2 = 20W
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
VPP - ESR * 4 * FS IO1 + IO2
=
1 = 15.78F 25mV - 5m * 4 * 1MHz 1.2A
IRMS(MAX) =
IO1 + IO2 = 6Arms 2
P = esr * IRMS2 = 5m * (0.6A)2 = 1.8mW
2511.2006.05.1.4
15
Dual 600mA, 1MHz Step-Down DC/DC Converter
AAT2511 Losses
AAT2511
The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an ambient temperature of 85C and a junction temperature of 120C.
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 * 1MHz * 0.6A + 60A) * 2.7V = 527mW
TJ(MAX) = TAMB + JA * PLOSS = 85C + (50C/W) * 527mW = 111C
Output 1 Enable
123
VIN
C41
R1 see Table 3
U1 AAT2511
1 2 3
LX1
12 11 10 9 8 7
EN1 FB1 SGND1 EN2 FB2 SGND2
VIN1 LX1 GND1 VIN2 LX2 GND2
L1 see Table 3 C3 10F LX2 L2 see Table 3 C11 4.7F C8 0.1F C7 0.01F C21 4.7F GND C6 0.01F VO2 VO1
C51
R3 see Table 3
4 5 6
R4 59.0k GND
R2 59.0k
321
Output 2 Enable
Figure 2: AAT2511 Evaluation Board Schematic.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10F.
16
2511.2006.05.1.4
Dual 600mA, 1MHz Step-Down DC/DC Converter
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
AAT2511
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)
4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 or 6.8 10 10
Table 3: Evaluation Board Component Values.
Figure 3: AAT2511 Evaluation Board Top Side.
Figure 4: AAT2511 Evaluation Board Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221k. 2511.2006.05.1.4
17
Dual 600mA, 1MHz Step-Down DC/DC Converter
Inductance (H)
4.7 10 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7
AAT2511
Manufacturer
Sumida Sumida MuRata MuRata MuRata Coilcraft Coilcraft Coiltronics Coiltronics Coiltronics Coiltronics
Part Number
CDRH3D16-4R7 CDRH3D16-100 LQH32CN4R7M23 LQH32CN4R7M33 LQH32CN4R7M53 LPO6610-472 LPO3310-472 SDRC10-4R7 SDR10-4R7 SD3118-4R7 SD18-4R7
Max DC Current (A)
0.90 0.55 0.45 0.65 0.65 1.10 0.80 1.53 1.30 0.98 1.77
DCR ()
0.11 0.21 0.20 0.15 0.15 0.20 0.27 0.117 0.122 0.122 0.082
Size (mm) LxWxH
3.8x3.8x1.8 3.8x3.8x1.8 2.5x3.2x2.0 2.5x3.2x2.0 2.5x3.2x1.55 5.5x6.6x1.0 3.3x3.3x1.0 4.5x3.6x1.0 5.7x4.4x1.0 3.1x3.1x1.85 5.2x5.2x1.8
Type
Shielded Shielded Non-Shielded Non-Shielded Non-Shielded 1mm 1mm 1mm Shielded 1mm Shielded Shielded Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer
MuRata MuRata MuRata
Part Number
GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39
Value
4.7F 10uF 22uF
Voltage
10V 6.3V 6.3V
Temp. Co.
X5R X5R X5R
Case
0805 0805 0805
Table 5: Surface Mount Capacitors.
18
2511.2006.05.1.4
Dual 600mA, 1MHz Step-Down DC/DC Converter Ordering Information
Package
TDFN33-12
AAT2511
Voltage
Channel 1 Channel 2
Marking1
QRXYY
Part Number (Tape and Reel)2
AAT2511IWP-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) 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. 2511.2006.05.1.4
19
Dual 600mA, 1MHz Step-Down DC/DC Converter Package Information
TDFN33-12
AAT2511
Index Area (D/2 x E/2)
Detail "B"
3.00 0.05
2.40 0.05
0.3 0.10 0.16 0.375 0.125 0.075 0.075 0.1 REF
Top View
Bottom View
Pin 1 Indicator (optional)
7.5 7.5
+ 0.05 0.8 -0.20
0.229 0.051
0.05 0.05
Option A: C0.30 (4x) max Chamfered corner
Option B: R0.30 (4x) max Round corner
Detail "B"
Side View
Detail "A"
All dimensions in millimeters.
(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. Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. 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 20
2511.2006.05.1.4
0.23 0.05
0.45 0.05
Detail "A"
3.00 0.05
1.70 0.05

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