AAT2512_202022B.pdf

DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
General Description
Features
The AAT2512 is a member of Skyworks' Total Power
Management IC (TPMIC™) product family. It 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.
• VIN Range: 2.7V to 5.5V
• Output Current:
▪ Channel 1: 400mA
▪ Channel 2: 400mA
• 98% Efficient Step-Down Converter
• Integrated Power Switches
• 100% Duty Cycle
• 1.4MHz Switching Frequency
• Internal Soft Start
• 150μs Typical Turn-On Time
• Over-Temperature Protection
• Current Limit Protection
• Available in TDFN33-12 Package
• -40°C to +85°C Temperature Range
Both regulators have independent input and enable pins.
Offered with fixed or adjustable output voltages, each
channel is designed to operate with 27μA (typical) of
quiescent current, allowing for high efficiency under light
load conditions.
The AAT2512 requires only three external components
(CIN, COUT, and LX) for each converter, minimizing cost
and real estate. Both channels are designed to deliver
400mA of load current and operate with a switching frequency of 1.4MHz, reducing the size of external components.
The AAT2512 is available in a Pb-free, 12-pin TDFN33
package and is rated over the -40°C to +85°C temperature range.
Applications
•
•
•
•
•
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core/ IO Power
PDAs and Handheld Computers
Typical Application
V OUT1
V BAT
C IN
VIN1
LX1
VIN2
FB1
L1
4.7μH
AAT2512
EN1
VOUT2
LX2
L2
4.7μH
EN2
COUT
4.7μF
FB2
GND
4.7μF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
1
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Pin Descriptions
Pin #
Symbol
1
EN1
2
FB1
3, 6, 7, 10
GND
4
EN2
5
FB2
8
9
11
12
LX2
VIN2
LX1
VIN1
Function
Enable pin for Channel 1. When connected low, it disables the channel and consumes less than 1μA of
current. When connected high, normal operation.
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. When connected low, it disables the channel and consumes less than 1μA of
current. When connected high, normal operation.
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
2
1
12
2
11
3
10
4
9
5
8
6
7
VIN1
LX1
GND
VIN2
LX2
GND
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202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC 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
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
2.0
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
3
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Electrical Characteristics1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
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
Min
IOUT = 0 to 400mA; VIN = 2.7V to 5.5V
2.7
-3.0
0.6
Per Channel
EN1 = EN2 = GND
VIN = 5.5V, VLX = 0 to VIN
VFB = 1.0V
Both Channels
VIN = 2.7V to 5.5V
From Enable to Output Regulation; Both Channels
Typ
Max
Units
27
5.5
3.0
VIN
70
1.0
1.0
0.2
1.2
0.45
0.40
0.2
1.4
150
V
%
V
μA
μA
μA
μA
A


%
MHz
μs
140
°C
15
°C
0.6
VIN = VFB = 5.5V
1.4
-1.0
1.0
V
V
μA
1. The AAT2512 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.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
Efficiency vs. Load
DC Regulation
(VOUT = 1.8V; L = 4.7μ
μH)
(VOUT = 1.8V)
1.0
100
Efficiency (%)
90
80
Output Error (%)
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
70
60
50
0.1
1
10
100
0.5
VIN = 4.2V
0.0
-1.0
0.1
1000
VIN = 3.6V
-0.5
VIN = 2.7V
1
10
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 2.5V; L = 6.8μ
μH)
100
(VOUT = 2.5V)
VIN = 2.7V
Output Error (%)
Efficiency (%)
VIN = 5.0V
80
VIN = 4.2V
VIN = 3.6V
60
VIN = 4.2V
0.5
VIN = 5.0V
0.0
VIN = 3.6V
-0.5
VIN = 3.0V
50
0.1
1
10
100
-1.0
1000
0.1
1
Output Current (mA)
1.0
Output Error (%)
90
Efficiency (%)
1000
(VOUT = 3.3V; L = 6.8µH)
VIN = 3.6V
VIN = 4.2V
80
VIN = 5.0V
60
50
0.1
100
DC Regulation
(VOUT = 3.3V; L = 6.8μ
μH)
70
10
Output Current (mA)
Efficiency vs. Load
100
1000
1.0
90
70
100
1
10
Output Current (mA)
100
1000
VIN = 5.0V
0.5
VIN = 4.2V
0.0
-0.5
-1.0
VIN = 3.6V
0.1
1
10
100
1000
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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5
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Typical Characteristics
5.0
Soft Start
Line Regulation
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
(VOUT = 1.8V)
0.40
1.6
0.30
3.0
1.2
0.20
2.0
1.0
1.0
0.8
0.0
0.6
VEN
VO
-1.0
0.4
-2.0
0.2
IL
-3.0
0.0
-4.0
-0.2
-5.0
-0.4
Accuracy (%)
1.4
4.0
Inductor Current
(bottom) (A)
Enable and Output Voltage
(top) (V)
EN1 = VIN; EN2 = GND.
IOUT = 10mA
0.10
0.00
-0.10
IOUT = 1mA
IOUT = 400mA
-0.20
-0.30
-0.40
2.5
3.0
3.5
μs/div)
Time (100μ
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Output Voltage Error vs. Temperature
Switching Frequency vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 400mA)
(VIN = 3.6V; VOUT = 1.8V)
2.0
15.0
9.0
1.0
Variation (%)
Output Error (%)
12.0
0.0
-1.0
6.0
3.0
0.0
-3.0
-6.0
-9.0
-12.0
-2.0
-40
-20
0
20
40
60
80
-15.0
-40
100
-20
0
Temperature (°°C)
80
100
50
VOUT = 1.8V
1.0
Supply Current (μ
μA)
Frequency Variation (%)
60
No Load Quiescent Current vs. Input Voltage
2.0
0.0
-1.0
VOUT = 2.5V
-2.0
VOUT = 3.3V
-3.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
6
40
Temperature (°°C)
Frequency vs. Input Voltage
-4.0
20
4.7
5.1
5.5
45
40
35
25°C
85°C
30
25
20
15
10
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
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5.1
5.5
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
P-Channel RDS(ON) vs. Input Voltage
750
750
700
700
120°C
650
100°C
RDS(ON) (mΩ
Ω)
650
RDS(ON) (mΩ
Ω)
N-Channel RDS(ON) vs. Input Voltage
600
550
85°C
500
450
25°C
400
120°C
600
550
500
85°C
450
400
25°C
350
350
300
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
6.0
3.0
Input Voltage (V)
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; C1 = 4.7μ
μF)
300mA
1mA
1.90
1.85
Output Voltage
(top) (V)
Output Voltage
(top) (V)
IO
1.80
1.75
VO
IO
0.4
0.3
IL
0.2
0.1
Load Transient Response
Load Transient Response
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; C1 = 10μ
μF)
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10μ
μF; C4 = 100pF)
0.4
0.3
0.2
0.1
Time (50μs/div)
1.825
Output Voltage
(top) (V)
300mA
1.850
1.800
1.775
VO
IO
400mA
300mA
0.4
0.3
IL
0.2
0.1
Load and Inductor Current
(200mA/div) (bottom)
400mA
Load and Inductor Current
(200mA/div) (bottom)
VO
IL
6.0
Time (50μs/div)
1.90
IO
400mA
300mA
Time (50μs/div)
1.75
5.5
Load and Inductor Current
(200mA/div) (bottom)
VO
0
1.80
5.0
Load Transient Response
IL
1.85
4.5
Load Transient Response
1.8
1.7
4.0
Input Voltage (V)
Load and Inductor Current
(200mA/div) (bottom)
1.9
3.5
(1mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10μ
μF; CFF = 100pF)
2.0
Output Voltage
(top) (V)
100°C
Time (50μs/div)
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7
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
1.82
6.0
1.80
5.0
1.79
4.5
1.78
4.0
1.77
3.5
1.76
3.0
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
5.5
Time (25μ
μs/div)
0.30
40
20
0.25
VO
0
0.20
-20
0.15
-40
0.10
-60
-80
0.05
IL
0.00
-100
-0.05
-120
-0.10
Time (10µs/div)
Output Ripple
0.9
40
20
0.8
VO
0
0.7
-20
0.6
-40
0.5
-60
0.4
0.3
-80
-100
IL
Inductor Current
(bottom) (A)
Output Voltage (AC coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
0.2
0.1
-120
Time (500ns/div)
8
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Inductor Current
(bottom) (A)
1.81
Output Voltage (AC coupled)
(top) (mV)
Line Response
(VOUT = 1.8V @ 400mA)
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Functional Block Diagram
FB1
VIN1
Err.
Amp.
DH
Comp.
LX1
Logic
Voltage
Reference
DL
Control
Logic
EN1
GND1
VIN2
See
Note
SGND1
FB2
Err.
Amp.
DH
Comp.
LX2
Logic
Voltage
Reference
Control
Logic
EN2
DL
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.
Functional Description
The AAT2512 is a high performance power management
IC comprised of two buck converters. Each channel has
independent input voltages and enable/disable 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 4.7μH and 4.7μF 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 400mA
current capability while maintaining over 90% efficiency
at full load. Light load efficiency is maintained at greater
than 80% down to 500μA of load current. Both channels
have excellent transient response, load, and line regulation. Transient response time is typically less than 20μs.
The AAT2512 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 1μA 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 140°C with 15°C of
hysteresis. The under-voltage lockout guarantees sufficient VIN bias and proper operation of all internal circuits
prior to activation.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
9
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Applications Information
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 17mW which gives
a 2.8% loss in efficiency for a 400mA 1.5V output.
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 AAT2512 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.
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.
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
m=
=
= 0.24
L
4.7μH
μsec
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.
0.75V
0.75 ⋅ VO
μsec
≈ 3 A ⋅ VO
L=
=
m
0.24A /μsec
=3
μsec
⋅ 2.5V = 7.5μH
A
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.
0.6V Adjustable With External Feedback
Fixed Output
⎛ VPP
⎞
- ESR ⋅ FS
⎝ IO
⎠
This equation provides an estimate for the input capacitor required for a single channel.
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 =
In this case, a standard 6.8μH value is selected. For highvoltage fixed versions (2.5V and above), m = 0.48A/μsec.
Table 1 displays inductor values for the AAT2512 fixed and
adjustable options.
Configuration
CIN =
V ⎞
VO ⎛
⋅ 1- O
VIN ⎝
VIN ⎠
1
⎛ VPP
⎞
- ESR • 4 • FS
⎝ IO1 + IO2
⎠
Because the AAT2512 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 · ⎛
⎝
VO1 ⎛
V ⎞
· 1 - O1 ⎞ + IO2 · ⎛
VIN ⎝
VIN ⎠ ⎠
⎝
VO2 ⎛
V ⎞
· 1 - O2
VIN ⎝
VIN ⎠
Output Voltage
Inductor
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
0.6V to 3.3V
2.2μH
4.7μH
6.8μH
4.7μH
Table 1: Inductor Values.
10
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202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
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
⎛
V ⎞
· 1- O
The term VIN ⎝ 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 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 AAT2512. 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.
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:
VO ⎛
V ⎞
· 1 - O = D ⋅ (1 - D) = 0.52 = 0.25
VIN ⎝
VIN ⎠
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
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:
COUT =
3 · ΔILOAD
VDROOP · FS
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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11
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Adjustable Output Resistor Selection
Thermal Calculations
For applications requiring an adjustable output voltage,
the 0.6V version can be programmed externally. Resistors
R1 through R4 of Figure 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.
There are three types of losses associated with the
AAT2512 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:
1
V
· (VIN(MAX) - VOUT)
IRMS(MAX) =
· OUT
L · F · VIN(MAX)
2· 3
The adjustable version of the AAT2512 in combination
with an external feedforward capacitor (C4 and C5 of
Figure 2) 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.
VOUT (V)
R2, R4 = 59k
R1, R3 (k)
R2, R4 = 221k
R1, R3
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
75K
113K
150K
187K
221K
261K
301K
332K
442K
464K
523K
715K
1.00M
⎛ VOUT ⎞
⎛ 1.5V ⎞
R1 = V
-1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
IQ is the AAT2512 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) · VO1 + RDSON(LS) · [VIN -VO1])
VIN
IO22 · (RDSON(HS) · VO2 + RDSON(LS) · [VIN -VO2])
VIN
+ (tsw · F · [IO1 + 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
Table 2: Adjustable Resistor Values
For Use With 0.6V Version.
12
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DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
PCB Layout
3.
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 VP and GND, as shown
in Figure 4. 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.
4.
5.
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 1.2mm grid.
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13
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Design Example
Specifications
VO1 = 2.5V @ 400mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA
VO2 = 1.8V @ 400mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.4 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= 72.3mA
L1 ⋅ F ⎝
VIN ⎠ 10μH ⋅ 1.4MHz ⎝ 4.2V⎠
IPK1 = IO1 +
ΔI1
= 0.4A + 0.036A = 0.44A
2
PL1 = IO12 ⋅ DCR = 0.4A2 ⋅ 210mΩ = 34mW
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= 156mA
L⋅F ⎝
VIN ⎠ 4.7μH ⋅ 1.4MHz ⎝ 4.2V⎠
IPK2 = IO2 +
ΔI2
= 0.4A + 0.078A = 0.48A
2
PL2 = IO22 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
2.5V Output Capacitor
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 3.2μF
VDROOP · FS 0.2V · 1.4MHz
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
2.5V · (4.2V - 2.5V)
·
= 21mArms
=
L · F · VIN(MAX)
2 · 3 10μH · 1.4MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (21mA)2 = 2.2μW
14
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DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
1.8V Output Capacitor
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 3.2μF
0.2V · 1.4MHz
VDROOP · FS
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
1.8V · (4.2V - 1.8V)
·
= 45mArms
=
L · F · VIN(MAX)
2 · 3 4.7μH · 1.4MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
1
=
= 6.8μF
⎛ VPP
⎞
⎛ 25mV
⎞
- ESR • 4 • FS
- 5mΩ • 4 • 1.4MHz
⎝ IO1 + IO2
⎠
⎝ 0.8A
⎠
IRMS(MAX) =
IO1 + IO2
= 0.4Arms
2
P = esr · IRMS2 = 5mΩ · (0.4A)2 = 0.8mW
AAT2512 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
=
0.42 · (0.725Ω · 2.5V + 0.7Ω · (2.7V - 2.5V)) + 0.42 · (0.725Ω · 1.8V + 0.7Ω · (2.7V - 1.8V))
2.7V
+ 5ns · 1.4MHz · 0.4A + 60μA) · 2.7V = 239mW
TJ(MAX) = TAMB + ΘJA • PLOSS = 85°C + (50°C/W) • 239mW = 97°C
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15
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Output 1 Enable
VIN
1 2 3
C41
R1
see Table 3
U1
AAT2512
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 3: AAT2512 Evaluation Board Schematic.
Figure 4: AAT2512 Evaluation Board Top Side.
Figure 5: AAT2512 Evaluation Board
Bottom Side.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10μF.
16
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DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Adjustable Version
(0.6V device)
R2, R4 = 59k
R2, R4 = 221k1
VOUT (V)
R1, R3 (k)
R1, R3 (k)
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
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
R2, R4 Not Used
VOUT (V)
R1, R3 (k)
L1, L2 (μH)
0.6-3.3V
0
4.7
Table 3: Evaluation Board Component Values.
Manufacturer
Part Number
Inductance
(μH)
Max DC
Current (A)
DCR
()
Size (mm)
LxWxH
Type
Sumida
Sumida
Sumida
Murata
Murata
Coilcraft
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-2R2
CDRH3D16-4R7
CDRH3D16-6R8
LQH2MCN4R7M02
LQH32CN4R7M23
LPO3310-472
SD3118-4R7
SD3118-6R8
SDRC10-4R7
2.2
4.7
6.8
4.7
4.7
4.7
4.7
6.8
4.7
1.20
0.90
0.73
0.40
0.45
0.80
0.98
0.82
1.30
0.072
0.105
0.170
0.80
0.20
0.27
0.122
0.175
0.122
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
Shielded
Shielded
Shielded
Non-Shielded
Non-Shielded
1mm
Shielded
Shielded
1mm 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 = 221kΩ.
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17
DATA SHEET
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Ordering Information
Voltage
Package
Channel 1
Channel 2
Marking1
Part Number (Tape and Reel)2
TDFN33-12
0.6V
0.6V
QKXYY
AAT2512IWP-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
AAT2512
Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter
Package Information
TDFN33-121
Index Area
0.43 ± 0.05
0.1 REF
C0.3
0.45 ± 0.05
2.40 ± 0.05
3.00 ± 0.05
Detail "A"
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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19