Skyworks AAT2511IWP-AA-T1 Dual 600ma, 1mhz step-down dc/dc converter Datasheet

DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
General Description
Features
The AAT2511 is a member of Skyworks' Total Power
Management IC (TPMIC™) 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.
For maximum battery life, each converter’s high-side
P-channel MOSFET conducts continuously when the
input voltage approaches dropout (100% duty cycle
operation).
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Both regulators have independent input and enable
inputs.
Applications
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 25μA quiescent operating current, which is
critical for maintaining high efficiency at light load.
The AAT2511 is available in a Pb-free, thermallyenhanced 12-pin TDFN33 package, and is rated over the
-40°C to +85°C temperature range.
•
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Up to 97% Efficiency
25μA 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 <1μA
Current Mode Operation
Internal Reference Soft Start
Short-Circuit Protection
Fast Turn-On (100μs Typical)
Over-Temperature Protection
3mm x 3mm, < 1mm high
TDFN33-12 Package
-40°C to +85°C Temperature Range
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor/DSP Core/IO Power
PDAs and Handheld Computers
Portable Media Players
Typical Application
AAT2511 Efficiency
VIN
U1
AAT2511
12
1.8V
1
L1
11
4.7μH
R1
118k
C1
10μF
2
3
R2
59.0k
10
VIN1
EN1
VIN2
EN2
LX1
LX2
FB1
FB2
SGND1
GND1
(VIN = 3.3V)
C8
0.1μF
SGND2
GND2
100
9
95
2.5V
4
L2
8
5
10μH
6
7
R4
59.0k
R3
187k
C2
10μF
Efficiency (%)
C3
10μF
90
85
2.5V
80
75
1.8V
70
65
60
0.1
1
10
100
1000
Load Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
1
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Pin Descriptions
Pin #
Symbol
1, 4
EN1, EN2
2, 5
FB1, FB2
3, 6
SGND1, SGND2
7, 10
GND2, GND1
8, 11
9, 12
LX2, LX1
VIN2, VIN1
EP
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 1μA. 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.
Pin Configuration
TDFN33-12
(Top View)
EN1
FB1
SGND1
EN2
FB2
SGND2
2
1
12
2
11
3
10
4
9
5
8
6
7
VIN1
LX1
GND1
VIN2
LX2
GND2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VFB
VEN
TJ
TLEAD
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
Units
6.0
-0.3 to VP + 0.3
-0.3 to VP + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
2
50
W
°C/W
Thermal Information
Symbol
PD
JA
Description
Maximum Power Dissipation
Thermal Resistance2
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
3
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Electrical Characteristics1
TA = -40°C to 85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol
Description
Conditions
Step-Down Converter Channels
VIN
Input Voltage
VUVLO
VOUT
VOUT
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLK
VLinereg
VFB
TS
FOSC
TSD
THYS
EN
VEN(L)
VEN(H)
IEN
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
Min
Typ
Max
Units
5.5
2.6
V
V
mV
V
%
V
μA
μA
mA


μA
%/V
mV
μs
MHz
°C
°C
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0 to 400mA, VIN = 2.7 - 5.5V
100
1.8
-3.0
0.6
No Load, 0.6V Adjustable Version, Per Channel
EN = SGND = GND
25
+3.0
VIN
50
1.0
600
0.45
0.4
VIN = 5.5V, VLX = 0 to VIN, EN = SGND = GND
VIN = 2.7V to 5.5V
0.6V Output, No Load, TA = 25°C
From Enable to Output Regulation
TA = 25°C
591
0.7
600
100
1.0
140
15
1
0.2
609
1.5
0.6
VIN = VFB = 5.5V
1.4
-1.0
1.0
V
V
μA
1. The AAT2511 is guaranteed to meet performance specifications over the -40°C to +85°C 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 Skyworks representative.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 3.3V; L = 10μ
μH)
(VOUT = 3.3V; L = 10μ
μH)
3.0
Output Error (%)
Efficiency (%)
100
VIN = 3.9V
90
VIN = 4.2V
80
70
60
0.1
1
10
100
2.0
0.0
-1.0
VIN = 3.9V
-2.0
-3.0
1000
VIN = 4.2V
1.0
0.1
1
10
Output Current (mA)
Output Error (%)
Efficiency (%)
100
1000
3.0
90
VIN = 3.0V
VIN = 3.6V
80
70
0.1
1
10
100
VIN = 3.3V
2.0
VIN = 3.6V
1.0
0.0
VIN = 3.0V
-1.0
-2.0
-3.0
1000
0.1
1
Output Current (mA)
10
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 1.5V; L = 4.7μ
μH)
(VOUT = 1.5V; L = 4.7μ
μH)
3.0
100
VIN = 2.7V
VIN = 3.6V
80
Output Error (%)
90
Efficiency (%)
1000
(VOUT = 2.5V; L = 10μ
μH)
VIN = 3.3V
VIN = 4.2V
70
60
50
100
DC Regulation
(VOUT = 2.5V; L = 10μ
μH)
60
1000
Output Current (mA)
Efficiency vs. Load
100
100
0.1
1
10
Output Current (mA)
100
1000
VIN = 4.2V
2.0
VIN = 3.6V
1.0
0.0
VIN = 2.7V
-1.0
-2.0
-3.0
0.1
1
10
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
5
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Output Voltage Error vs. Temperature
Frequency vs. Input Voltage
(VIN = 3.6V; VO = 2.5V)
(VOUT = 1.8V)
2.0
Frequency Variation (%)
1.0
1.5
Output Error (%)
0.5
0.0
-0.5
-1.0
-1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-40
-2.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-20
0
20
Switching Frequency vs. Temperature
100
(VO = 1.8V)
0.20
35
Supply Current (μ
μA)
Variation (%)
80
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
0.10
0.00
-0.10
-0.20
-40
85°C
30
25°C
25
20
-40°C
15
-20
0
20
40
60
80
2.5
100
3.0
3.5
4.0
4.5
5.0
5.5
Temperature (°°C)
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
6.0
750
750
700
700
120°C
650
100°C
RDS(ON) (mΩ
Ω)
650
RDS(ON) (mΩ
Ω)
60
Temperature (°°C)
Input Voltage (V)
600
550
85°C
500
450
25°C
400
120°C
600
100°C
550
500
85°C
450
400
25°C
350
350
300
300
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
6
40
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
5.5
6.0
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Load Transient Response
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22μ
μF)
1.3
1.1
300mA
30mA
0.9
0.7
0.5
0.3
0.1
-0.1
2.65
1.5
2.55
Output Voltage
(top) (V)
1.5
1.3
0.7
0.5
2.25
0.3
2.15
0.1
2.05
-0.1
Time (25μs/div)
Line Transient
Line Regulation
(VOUT = 1.5V)
7.0
2.55
6.5
6.0
5.5
2.40
5.0
2.35
4.5
2.30
2.25
4.0
2.20
3.5
2.15
1.5
Accuracy (%)
2.60
2
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
(VOUT = 2.5V @ 500mA)
2.45
0.9
30mA
2.35
Time (25μs/div)
2.50
1.1
300mA
2.45
Load and Inductor Current
(200mA/div) (bottom)
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
Load and Inductor Current
(200mA/div) (bottom)
Output Voltage
(top) (V)
(30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22μ
μF)
IOUT = 600mA
1
IOUT = 100mA
0.5
0
IOUT = 10mA
-0.5
-1
3.0
2.5
Time (25μ
μs/div)
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Soft Start
Output Ripple
(VIN = 3.6V; VOUT = 1.5V; L = 4.7μ
μH)
0.8
0
0.7
-20
0.6
0.5
-40
0.4
-60
0.3
-80
0.2
-100
0.1
-120
Time (250ns/div)
4.0
3.5
3.0
3.0
2.0
2.5
1.0
2.0
0.0
1.5
-1.0
1.0
-2.0
0.5
-3.0
0.0
-4.0
-0.5
Inductor Current
(bottom) (A)
20
Enable and Output Voltage
(top) (V)
0.9
40
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
Time (50μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
7
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Functional Block Diagram
FB1
VIN1
Err.
Amp.
DH
Comp.
LX1
Logic
Voltage
Reference
DL
Control
Logic
EN1
SGND1
GND1
VIN2
See
Note
FB2
Err.
Amp.
DH
Comp.
LX2
Logic
Voltage
Reference
DL
Control
Logic
EN2
GND2
See
Note
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
8
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 500μA load.
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, nonswitching state with a bias current of less than 1μA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
VIN = 2.7 - 5.5V
C3
10μF
12
9
VIN1
VIN2
EN1
EN2
1
2.5V at 600mA
L1
4.7μH
C8
0.1μF
U1
AAT2511
4
11
LX1
LX2
FB1
FB2
2
5
3
1.8V at 600mA
L2
8
4.7μH
6
SGND1 SGND2
C1
4.7μF
10
C2
4.7μF
7
GND1
GND2
L1, L2 Sumida CDRH3D16-4R7 C1, C2 Murata GRM219R61A475KE19
C3 Murata GRM21BR60J106KE19
Figure 1: AAT2511 Adjustable Output with
Enhanced Transient Response.
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
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.
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
140°C with 15°C of hysteresis.
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/μsec.
This equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and 4.7μH
inductor.
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7μH
μsec
m=
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 7.5μH.
L=
0.75V
0.75 ⋅ VO
μsec
≈ 3 A ⋅ VO
=
m
0.24A /μsec
=3
μsec
⋅ 2.5V = 7.5μH
A
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202021B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
9
DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
In this case, a standard 10μH value is selected.
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 4.7μH 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.
Input Capacitor
Select a 4.7μF to 10μF 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.
CIN =
V ⎞
VO ⎛
⋅ 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR ⋅ FS
⎝ IO
⎠
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 10μF 6.3V X5R ceramic capacitor with 5V DC applied is actually about 6μF.
The maximum input capacitor RMS current is:
IRMS = IO1 · ⎛
⎝
Configuration
Output
Voltage
0.6V Adjustable
With External
Resistive Divider
0.6V to
2.0V
2.5V
Inductor
Slope
Compensation
4.7μH
0.24A/μsec
10μH
0.24A/μsec
Table 1: Inductor Values.
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.
CIN =
10
1
⎛ VPP
⎞
- ESR • 4 • FS
⎝ IO1 + IO2
⎠
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.
VO
This equation provides an estimate for the input capacitor required for a single channel.
VO1 ⎛
V ⎞
· 1 - O1 ⎞ + IO2 · ⎛
VIN ⎝
VIN ⎠ ⎠
⎝
⎛
VO ⎞
The term V · ⎝1 - 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
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).
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC 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 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.
Output Capacitor
The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7μF to
10μF 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:
COUT =
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) =
1
VOUT · (VIN(MAX) - VOUT)
L · F · VIN(MAX)
2· 3
·
Dissipation due to the RMS current in the ceramic output
capacitor ESR is typically minimal, resulting in less than
a few degrees rise in hot spot temperature.
Adjustable Output Resistor Selection
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 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
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.
3 · ΔILOAD
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 4.7μF. This is due to
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
VOUT (V)
R2, R4 = 59kΩ
R1, R3 (kΩ)
R2, R4 = 221kΩ
R1, R3 (kΩ)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75
113
150
187
221
261
301
332
442
464
523
715
Table 2: Adjustable Resistor Values
For Use With 0.6V Version.
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 50°C/W.
TJ(MAX) = PTOTAL • ΘJA + TAMB
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:
PTOTAL =
+
IO12 · (RDSON(HS) · VO1 + RDSON(LS) · [VIN -VO1])
PCB Layout
The following guidelines should be used to insure a
proper layout.
1.
2.
VIN
IO22 · (RDSON(HS) · VO2 + RDSON(LS) · [VIN -VO2])
VIN
3.
+ (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:
4.
5.
12
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.
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.
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.
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DATA SHEET
AAT2511
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 = 2.7V to 4.2V (3.6V nominal)
FS = 1.0 MHz
TAMB = 85°C
2.5V VO1 Output Inductor
L1 = 3
μsec
μsec
⋅ VO1 = 3
⋅ 2.5V = 7.5μH (see Table 1)
A
A
For Sumida inductor CDRH3D16, 10μH, DCR = 210m.
ΔI1 =
⎛ 2.5V⎞
VO ⎛
V ⎞
2.5V
⋅ 1 - O1 =
⋅ 1= 100mA
L1 ⋅ F ⎝
VIN ⎠ 10μH ⋅ 1.0MHz ⎝ 4.2V⎠
IPK1 = IO1 +
ΔI1
= 0.6A + 0.05A = 0.65A
2
PL1 = IO12 ⋅ DCR = (0.4A)2 ⋅ 210mΩ = 76mW
1.8V VO2 Output Inductor
L2 = 3
μsec
μsec
⋅ VO2 = 3
⋅ 1.8V = 5.4μH (see Table 1)
A
A
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m.
ΔI2 =
⎛ 1.8V ⎞
VO2 ⎛
V ⎞
1.8V
⋅ 1 - O2 =
⋅ ⎝1 = 218mA
L⋅F ⎝
VIN ⎠ 4.7μH ⋅ 1.0MHz
4.2V⎠
IPK2 = IO2 +
ΔI2
= 0.6A + 0.11A = 0.71A
2
PL2 = IO22 ⋅ DCR = (0.6A)2 ⋅ 105mΩ = 38mW
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
2.5V Output Capacitor
COUT =
3 · ΔILOAD
3 · 0.6A
=
= 9μF
0.2V · 1MHz
VDROOP · FS
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
2.5V · (4.2V - 2.5V)
·
= 29mArms
=
10μH
· 1MHz · 4.2V
L · F · VIN(MAX)
2· 3
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (29mA)2 = 4.2μW
1.8V Output Capacitor
COUT =
3 · ΔILOAD
3 · 0.6A
=
= 9μF
VDROOP · FS
0.2V · 1MHz
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
1.8V · (4.2V - 1.8V)
·
= 63mArms
=
4.7μH
· 1.0MHz · 4.2V
L
·
F
·
V
2· 3
2· 3
IN(MAX)
1
·
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
⎛ VPP
⎞
- ESR • 4 • FS
⎝ IO1 + IO2
⎠
IRMS(MAX) =
=
1
= 15.78μF
⎛ 25mV
⎞
- 5mΩ • 4 • 1MHz
⎝ 1.2A
⎠
IO1 + IO2
= 6Arms
2
P = esr · IRMS2 = 5mΩ · (0.6A)2 = 1.8mW
14
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
AAT2511 Losses
The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an ambient temperature of 85°C and
a junction temperature of 120°C.
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 · (0.725Ω · 2.5V + 0.7Ω · (2.7V - 2.5V)) + 0.62 · (0.725Ω · 1.8V + 0.7Ω · (2.7V - 1.8V))
2.7V
+ 5ns · 1MHz · 0.6A + 60μA) · 2.7V = 527mW
TJ(MAX) = TAMB + ΘJA • PLOSS = 85°C + (50°C/W) • 527mW = 111°C
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Output 1 Enable
VIN
1 2 3
C41
R1
see Table 3
U1
AAT2511
1
2
3
C51
R3
see Table 3
4
5
6
R4
59.0k
EN1
FB1
SGND1
VIN1
LX1
GND1
EN2
VIN2
FB2
LX2
SGND2
R2
59.0k
GND2
LX1
12
L1
see Table 3
11
10
VO1
C3
LX2
9
10μF
8
VO2
L2
see Table 3
C11
4.7μF
7
C8
C7
0.01μF
C6
0.01μF
C21
4.7μF
0.1μF
GND
GND
3 2 1
Output 2 Enable
Figure 2: AAT2511 Evaluation Board Schematic.
Figure 3: AAT2511 Evaluation Board Top Side.
Figure 4: AAT2511 Evaluation Board
Bottom Side.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10μF.
16
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Adjustable Output
(0.6V device)
VOUT (V)
R1, R3 (kΩ)
R1, R3 (kΩ)
L1, L2 (μH)
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
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75.0
113
150
187
221
261
301
332
442
464
523
715
1000
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.
Manufacturer
Part Number
Inductance
(μH)
Sumida
Sumida
MuRata
Murata
Murata
Coilcraft
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-4R7
CDRH3D16-100
LQH32CN4R7M23
LQH32CN4R7M33
LQH32CN4R7M53
LPO6610-472
LPO3310-472
SDRC10-4R7
SDR10-4R7
SD3118-4R7
SD18-4R7
4.7
10
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
Max DC
Current
(A)
DCR
(Ω)
Size (mm)
LxWxH
Type
0.90
0.55
0.45
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.21
0.20
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
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
Shielded
Shielded
Non-Shielded
Non-Shielded
Non-Shielded
1mm
1mm
1mm Shielded
1mm Shielded
Shielded
Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
Murata
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7μF
10uF
22uF
10V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 5: Surface Mount Capacitors.
1. For reduced quiescent current, R2 and R4 = 221k.
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Ordering Information
Voltage
Package
Channel 1
Channel 2
Marking1
Part Number (Tape and Reel)2
TDFN33-12
0.6V
0.6V
QRXYY
AAT2511IWP-AA-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Legend
Voltage
Code
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
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.
18
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DATA SHEET
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Package Information
TDFN33-12
Index Area
0.40 ± 0.05
Detail "A"
C0.3
0.45 ± 0.05
2.40 ± 0.05
3.00 ± 0.05
0.1 REF
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
0.23 ± 0.05
Pin 1 Indicator
(optional)
0.05 ± 0.05
0.23 ± 0.05
0.75 ± 0.05
Detail "A"
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.
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