Analogic AAT2512IWP-IH-T1 Dual 400ma high frequency buck converter Datasheet

AAT2512
Dual 400mA High Frequency Buck Converter
General Description
Features
The AAT2512 is a member of AnalogicTech's 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 singlecell lithium-ion/polymer batteries.
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•
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.
•
•
•
•
•
•
•
•
•
•
SystemPower™
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
Applications
•
•
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Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core/ IO Power
PDAs and Handheld Computers
Typical Application
V BAT
C IN
VIN1
LX1
VIN2
FB1
L1
4.7µH
AAT2512
EN1
LX2
EN2
FB2
GND
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V OUT1
VOUT2
L2
4.7µH
COUT
4.7µF
4.7µF
1
AAT2512
Dual 400mA High Frequency Buck Converter
Pin Descriptions
Pin #
Symbol
1
EN1
2
FB1
3, 6, 7, 10
4
GND
EN2
5
FB2
8
LX2
9
11
VIN2
LX1
12
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
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VFB
VEN
TJ
TLEAD
Description
Input Voltages to GND
LX to GND
FB1 and FB2 to GND
EN1 and EN2 to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
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
θJA
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.
2512.2006.06.1.4
3
AAT2512
Dual 400mA High Frequency Buck Converter
Electrical Characteristics1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
VIN
Input Voltage
VOUT
Output Voltage Tolerance
VOUT
IQ
ISHDN
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
ILX_LEAK
IFB
ILIM
RDS(ON)H
RDS(ON)L
ΔVLINE
FOSC
TS
TSD
THYS
VEN(L)
VEN(H)
IEN
Start-Up Time
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
Conditions
IOUT = 0 to 400mA;
VIN = 2.7V to 5.5V
Min
Typ
Max Units
2.7
5.5
V
-3.0
3.0
%
VIN
70
1.0
1.0
0.2
1.2
0.45
0.40
0.2
1.4
V
µA
µA
µA
µA
A
Ω
Ω
%
MHz
150
µs
140
°C
15
°C
0.6
Per Channel
EN1 = EN2 = GND
VIN = 5.5V, VLX = 0 to VIN
VFB = 1.0V
Both Channels
27
VIN = 2.7V to 5.5V
From Enable to Output Regulation;
Both Channels
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
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck 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
VIN = 3.6V
-0.5
-1.0
0.1
1000
VIN = 2.7V
1
Output Current (mA)
Efficiency vs. Load
DC Regulation
1.0
Output Error (%)
Efficiency (%)
90
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 (%)
Efficiency (%)
90
VIN = 4.2V
80
VIN = 5.0V
60
1
10
Output Current (mA)
2512.2006.06.1.4
1000
(VOUT = 3.3V; L = 6.8µH)
VIN = 3.6V
50
0.1
100
DC Regulation
(VOUT = 3.3V; L = 6.8μ
μH)
70
10
Output Current (mA)
Efficiency vs. Load
100
1000
(VOUT = 2.5V)
VIN = 2.7V
70
100
Output Current (mA)
(VOUT = 2.5V; L = 6.8μ
μH)
100
10
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)
5
AAT2512
Dual 400mA High Frequency Buck Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
Line Regulation
(VOUT = 1.8V)
0.40
1.6
0.30
1.2
0.20
2.0
1.0
1.0
0.8
0.0
0.6
-1.0
0.4
-2.0
0.2
VEN
VO
IL
-3.0
0.0
-4.0
-0.2
-5.0
-0.4
Accuracy (%)
1.4
3.0
4.0
Inductor Current
(bottom) (A)
Enable and Output Voltage
(top) (V)
5.0
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
IOUT = 10mA
0.10
0.00
-0.10
IOUT = 1mA
IOUT = 400mA
-0.20
-0.30
-0.40
2.5
3.0
3.5
Time (100μ
μs/div)
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
-40°C
15
10
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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AAT2512
Dual 400mA High Frequency Buck Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
750
700
700
120°C
650
100°C
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
650
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
400mA
300mA
0.4
0.3
IL
0.2
0.1
Time (50μs/div)
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
IL
0.2
0.1
Time (50μs/div)
2512.2006.06.1.4
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
IO
6.0
Time (50μs/div)
1.90
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)
7
AAT2512
Dual 400mA High Frequency Buck Converter
Typical Characteristics
EN1 = VIN; EN2 = GND.
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
6.0
5.5
1.80
5.0
1.79
4.5
1.78
4.0
1.77
3.5
1.76
3.0
Time (25μ
μs/div)
40
20
0.30
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
Inductor Current
(bottom) (A)
1.81
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
1.82
Output Voltage (AC coupled)
(top) (mV)
Line Response
(VOUT = 1.8V @ 400mA)
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
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
Functional Block Diagram
FB1
VIN1
DH
Comp.
Err.
Amp.
LX1
Logic
Voltage
Reference
SGND1
DL
Control
Logic
EN1
GND1
VIN2
See
Note
FB2
DH
Comp.
Err.
Amp.
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.
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.
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.
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 overtemperature 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.
2512.2006.06.1.4
9
AAT2512
Dual 400mA High Frequency Buck 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 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.
m=
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7μH
μsec
The 4.7µH CDRH3D16 series inductor selected
from Sumida has a 105mΩ 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.
Input Capacitor
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=
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.
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.
0.75V
0.75 ⋅ VO
μsec
≈ 3 A ⋅ VO
=
m
0.24A /μsec
CIN =
μsec
=3
⋅ 2.5V = 7.5μH
A
In this case, a standard 6.8µH value is selected.
For high-voltage fixed versions (2.5V and above),
m = 0.48A/µsec. Table 1 displays inductor values
for the AAT2512 fixed and adjustable options.
Configuration
0.6V Adjustable With
External Feedback
Fixed Output
V ⎞
VO ⎛
⋅ 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR ⋅ FS
⎝ IO
⎠
This equation provides an estimate for the input
capacitor required for a single channel.
Output Voltage
Inductor
1V, 1.2V
2.2µH
1.5V, 1.8V
4.7µH
2.5V, 3.3V
6.8µH
0.6V to 3.3V
4.7µH
Table 1: Inductor Values.
10
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck 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.
1
CIN =
⎛ 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 ⎠ ⎠
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.
I
+I
IRMS(MAX) = O1(MAX) O2(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
⎛
VO ⎞
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
capacitor RMS current ripple are a maximum at
50% duty cycle.
2512.2006.06.1.4
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.
11
AAT2512
Dual 400mA High Frequency Buck Converter
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 =
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 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
2· 3
·
VOUT · (VIN(MAX) - VOUT)
L · F · VIN(MAX)
Dissipation due to the RMS current in the ceramic
output capacitor ESR is typically minimal, resulting in
less than a few degrees rise in hot spot temperature.
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 2 program
the output to regulate at a voltage higher than 0.6V.
12
To limit the bias current required for the external
feedback resistor string, the minimum suggested
value for R2 and R4 is 59kΩ. 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 59kΩ for good noise immunity or 221kΩ
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 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.
Ω
R2, R4 = 59kΩ
Ω
R2, R4 = 221kΩ
VOUT (V)
Ω)
R1, R3 (kΩ
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
Table 2: Adjustable Resistor Values
For Use With 0.6V Version.
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
Thermal Calculations
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:
Given the total losses, the maximum junction temperature can be derived from the θJA for the
TDFN33-12 package which is 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + 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 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)
+
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.
2512.2006.06.1.4
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.
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.
13
AAT2512
Dual 400mA High Frequency Buck Converter
Design Example
Specifications
VO1 = 2.5V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 300mA
VO2 = 1.8V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 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
A
A
(see Table 1)
For Sumida inductor CDRH3D16, 10µH, DCR = 210mΩ.
ΔI1 =
⎛ 2.5V⎞
VO ⎛
V ⎞
2.5V
⋅ 1 - O1 =
⋅ ⎝1 = 72.3mA
VIN ⎠ 10μH ⋅ 1.4MHz
4.2V⎠
L1 ⋅ F ⎝
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 = 105mΩ.
ΔI2 =
⎛ 1.8V ⎞
VO2 ⎛
V ⎞
1.8V
⋅ 1 - O2 =
⋅ 1= 156mA
VIN ⎠ 4.7μH ⋅ 1.4MHz ⎝ 4.2V⎠
L⋅F ⎝
IPK2 = IO2 +
ΔI2
= 0.4A + 0.078A = 0.48A
2
PL2 = IO22 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
14
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
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
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
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO1 + IO2
⎠
IRMS(MAX) =
=
1
= 6.8μF
⎛ 25mV
⎞
- 5mΩ · 4 · 1.4MHz
⎝ 0.8A
⎠
IO1 + IO2
= 0.4Arms
2
P = esr · IRMS2 = 5mΩ · (0.4A)2 = 0.8mW
2512.2006.06.1.4
15
AAT2512
Dual 400mA High Frequency Buck Converter
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
Output 1 Enable
VIN
1 2 3
R1
see Table 3
C41
U1
AAT2512
1
2
1
C5
3
R3
see Table 3
4
5
6
R4
59.0k
EN1
VIN1
FB1
LX1
SGND1
GND1
EN2
VIN2
FB2
LX2
SGND2
GND2
LX1
12
L1
see Table 3
11
VO1
C3
10
10μF
9
8
LX2
VO2
L2
see Table 3
C11
4.7μF
7
R2
59.0k
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.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10µF.
16
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
Adjustable Version
(0.6V device)
Ω
R2, R4 = 59kΩ
Ω1
R2, R4 = 221kΩ
VOUT (V)
Ω)
R1, R3 (kΩ
Ω)
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
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)
Ω)
R1, R3 (kΩ
L1, L2 (µH)
0.6-3.3V
0
4.7
Table 3: Evaluation Board Component Values.
Figure 4: AAT2512 Evaluation Board Top Side.
Figure 5: AAT2512 Evaluation Board
Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221kΩ.
2512.2006.06.1.4
17
AAT2512
Dual 400mA High Frequency Buck Converter
Manufacturer
Sumida
Sumida
Sumida
MuRata
MuRata
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Part Number
Inductance
(µH)
Max DC
Current (A)
DCR
Ω)
(Ω
Size (mm)
LxWxH
Type
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
MuRata
MuRata
MuRata
Part Number
Value
Voltage
Temp. Co.
Case
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7µF
10uF
22uF
10V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 5: Surface Mount Capacitors.
18
2512.2006.06.1.4
AAT2512
Dual 400mA High Frequency Buck Converter
Ordering Information
Voltage
Package
Channel 1
Channel 2
Marking1
Part Number (Tape and Reel)2
TDFN33-12
TDFN33-12
0.6V
1.8V
0.6V
1.6V
QKXYY
QYXYY
AAT2512IWP-AA-T1
AAT2512IWP-IH-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Legend
Voltage
Adjustable
(0.6V)
0.9
1.2
1.5
1.8
1.9
2.5
2.6
2.7
2.8
2.85
2.9
3.0
3.3
4.2
Code
A
B
E
G
I
Y
N
O
P
Q
R
S
T
W
C
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2512.2006.06.1.4
19
AAT2512
Dual 400mA High Frequency Buck Converter
TDFN33-12
2.40 ± 0.05
Detail "B"
3.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10 0.16 0.375 ± 0.125
0.075 ± 0.075
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Detail "A"
0.45 ± 0.05
0.1 REF
0.05 ± 0.05
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "B"
Detail "A"
All dimensions in millimeters.
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20
2512.2006.06.1.4