AAT1146IGV-0.6-T1 [ANALOGICTECH]
Fast Transient 400mA Step-Down Converter; 快速瞬态400毫安降压转换器
| 型号： | AAT1146IGV-0.6-T1 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | Fast Transient 400mA Step-Down Converter |
| 文件： | 总20页 (文件大小：663K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
General Description
Features
The AAT1146 SwitchReg is a 1.4MHz step-down con-
verter with an input voltage range of 2.7V to 5.5V and
output voltage as low as 0.6V. It is optimized to react
quickly to a load variation.
• VIN Range: 2.7V to 5.5V
• VOUT Fixed or Adjustable from 0.6V to VIN
• 27μA No Load Quiescent Current
• Up to 98% Efficiency
• 400mA Max Output Current
• 1.4MHz Switching Frequency
• 120μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
The AAT1146 is available in fixed voltage versions with
internal feedback and a programmable version with
external feedback resistors. It can deliver 400mA of load
current while maintaining a low 27μA no load quiescent
current. The 1.4MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
The AAT1146 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
• SC70JW-8 and SOT23-5 Packages
• Temperature Range: -40°C to +85°C
The AAT1146 is available in the Pb-free, space-saving
2.0x2.1mm SC70JW-8 and SOT23-5 packages 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
• USB Devices
Typical Application (Fixed Output Voltage)
U1
AAT1146
L1
VO
VIN
LX
OUT
VIN
4.7µH
EN
C2
4.7µF
C1
4.7µF
PGND
PGND
AGND
PGND
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Pin Descriptions
Pin #
SC70JW-8
SOT23-5
Symbol
Function
1
2
EN
Enable pin.
Feedback input pin. This pin is connected either directly to the converter output or to an
external resistive divider for an adjustable output.
Input supply voltage for the converter.
Switching node. Connect the inductor to this pin. It is internally connected to the drain of
both high- and low-side MOSFETs.
2
3
4
4
5
3
OUT
VIN
LX
5
AGND
PGND
Non-power signal ground pin.
Main power ground return pins. Connect to the output and input capacitor return.
1
6, 7, 8
Pin Configuration
SC70JW-8
(Top View)
SOT23-5
(Top View)
8
1
2
3
4
PGND
EN
5
1
VIN
GND
EN
7
6
5
OUT
VIN
LX
PGND
PGND
AGND
2
3
4
LX
OUT
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VIN
VLX
VOUT
VEN
TJ
Input Voltage GND
LX to GND
OUT to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
6.0
V
V
V
V
°C
°C
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-40 to 150
TLEAD
300
Thermal Information
Symbol
Description
Value
Units
SC70JW-8
SOT23-5
SC70JW-8
SOT23-5
625
667
160
150
PD
Maximum Power Dissipation2, 3
mW
θJA
Thermal Resistance2
°C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. SC70JW-8: Derate 6.25mW/°C above 25°C.
SOT23-5: Derate 6.67mW/°C above 25°C.
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Electrical Characteristics1
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol Description
Step-Down Converter
Conditions
Min Typ Max Units
VIN
Input Voltage
2.7
5.5
2.7
V
V
VIN Rising
VUVLO
UVLO Threshold
Hysteresis
VIN Falling
100
27
mV
V
1.8
-3.0
0.6
VOUT
VOUT
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
ΔVLinereg
VOUT
IOUT
ROUT
TS
FOSC
TSD
THYS
Output Voltage Tolerance
Output Voltage Range
Quiescent Current
IOUT = 0 to 400mA, VIN = 2.7V to 5.5V
+3.0
VIN
70
%
V
No Load, 0.6V Adjustable Version
EN = AGND = PGND
μA
μA
mA
Ω
Shutdown Current
1.0
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
Line Regulation
Out Threshold Voltage Accuracy
Out Leakage Current
Out Impedance
Start-Up Time
Oscillator Frequency
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
600
0.45
0.40
Ω
VIN = 5.5V, VLX = 0 to VIN, EN = GND
VIN = 2.7V to 5.5V
0.6V Output, No Load; TA = 25°C
0.6V Output
>1.0V Output2
1
μA
%/V
mV
μA
kΩ
μs
MHz
°C
°C
0.1
600
591
250
1.0
609
0.2
From Enable to Output Regulation
TA = 25°C
150
1.4
140
15
2.0
EN
VEN(L)
VEN(H)
IEN
Enable Threshold Low
Enable Threshold High
Input Low Current
0.6
1.0
V
V
μA
1.4
-1.0
VIN = VOUT = 5.5V
1. The AAT1146 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
2. The AAT1146 fixed output versions have the output set to different voltages.
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7μH)
DC Regulation
(VOUT = 1.8V)
100
1.0
VIN = 2.7V
90
0.5
VIN = 4.2V
VIN = 4.2V
80
VIN = 3.6V
0.0
70
60
50
VIN = 3.6V
VIN = 2.7V
-0.5
-1.0
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 6.8μH)
DC Regulation
(VOUT = 2.5V)
100
90
80
70
60
50
1.0
0.5
VIN = 2.7V
VIN = 4.2V
VIN = 5.0V
VIN = 5.0V
VIN = 4.2V
0.0
VIN = 3.6V
VIN = 3.6V
-0.5
-1.0
VIN = 3.0V
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8μH)
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8μH)
100
100
VIN = 3.6V
VIN = 3.6V
90
80
70
60
50
90
80
70
60
50
VIN = 4.2V
VIN = 4.2V
VIN = 5.0V
VIN = 5.0V
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Typical Characteristics
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
Line Regulation
(VOUT = 1.8V)
0.40
0.30
5.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
VEN
VO
4.0
3.0
IOUT = 10mA
0.20
2.0
0.10
0.00
1.0
0.0
-0.10
-1.0
-2.0
-3.0
-4.0
-5.0
IOUT = 1mA
-0.20
IOUT = 400mA
IL
-0.30
-0.40
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Time (100μs/div)
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 400mA)
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
2.0
1.0
15.0
12.0
9.0
6.0
3.0
0.0
0.0
-3.0
-6.0
-9.0
-12.0
-15.0
-1.0
-2.0
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
Temperature (°C)
Temperature (°°C)
Frequency vs. Input Voltage
No Load Quiescent Current vs. Input Voltage
2.0
1.0
50
45
40
35
VOUT = 1.8V
0.0
25°C
85°C
-1.0
-2.0
-3.0
-4.0
30
25
20
15
10
VOUT = 2.5V
VOUT = 3.3V
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
700
750
700
650
600
550
500
450
400
350
300
650
120°C
100°C
120°C
100°C
600
550
500
85°C
85°C
450
25°C
400
25°C
350
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Load Transient Response
(1mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
Load Transient Response
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; C1 = 4.7μF)
C1 = 10μF; CFF = 100pF)
2.0
1.9
1.8
1.7
1.90
1.85
1.80
1.75
VO
VO
IO
IO
300mA
400mA
300mA
1mA
IL
0.4
0.3
0.2
0.1
IL
0
Time (50μs/div)
Time (50μs/div)
Load Transient Response
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; C1 = 10μF)
Load Transient Response
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10μμF; C4 = 100pF)
1.850
1.90
1.85
1.80
1.75
1.825
1.800
1.775
VO
IO
VO
IO
400mA
400mA
300mA
300mA
0.4
0.3
0.2
0.1
0.4
0.3
0.2
0.1
IL
IL
Time (50μs/div)
Time (50μs/div)
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Typical Characteristics
Line Response
(VOUT = 1.8V @ 400mA)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
40
20
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
1.82
1.81
1.80
1.79
1.78
1.77
6.0
5.5
5.0
4.5
4.0
3.5
3.0
VO
0
-20
-40
-60
-80
-100
-120
IL
1.76
Time (25μs/div)
Time (10µs/div)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
40
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
20
VO
0
-20
-40
-60
-80
IL
-100
-120
Time (500ns/div)
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Functional Block Diagram
VIN
OUT
See note
Err
Amp
.
DH
LX
Voltage
Logic
Reference
DL
INPUT
EN
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly
to the internal error amplifier.
tional feed-forward capacitor (CFF) can also be added to
the external feedback to provide improved transient
response (see Figure 1).
Functional Description
The AAT1146 is a high performance 400mA 1.4MHz
monolithic step-down converter. It has been designed
with the goal of minimizing external component size and
optimizing efficiency over the complete load range.
Apart from the small bypass input capacitor, only a small
L-C filter is required at the output. Typically, a 4.7μH
inductor and a 4.7μF ceramic capacitor are recommend-
ed (see table of values).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDSON drop of the P-channel high-side MOSFET.
The input voltage range is 2.7V to 5.5V. The converter
efficiency has been optimized for all load conditions,
ranging from no load to 400mA.
The fixed output version requires only three external
power components (CIN, COUT, and L). The adjustable ver-
sion can be programmed with external feedback to any
voltage, ranging from 0.6V to the input voltage. An addi-
The internal error amplifier and compensation provides
excellent transient response, load, and line regulation.
Soft start eliminates any output voltage overshoot when
the enable or the input voltage is applied.
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
1
2
3
VIN
Enable
CFF
U1
AAT1146
1
2
3
4
8
7
6
5
EN
PGND
OUT PGND
R1 118k
L1
VIN
LX
PGND
AGND
VOUT
4.7µH
C1
C2
4.7µF
R2
59k
10µF
GND
GND2
LX
U1 AAT1146 SC70JW-8
L1 CDRH3D16-4R7
C1 10µF 10V 0805 X5R
C2 4.7µF 10V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
Current Limit and
Over-Temperature Protection
The AAT1146 is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
For overload conditions, the peak input current is limit-
ed. To minimize power dissipation and stresses under
current limit and short-circuit conditions, switching is
terminated after entering current limit for a series of
pulses. Switching is terminated for seven consecutive
clock cycles after a current limit has been sensed for a
series of four consecutive clock cycles.
The output of the voltage error amplifier programs the
current mode loop for the necessary peak switch current
to force a constant output voltage for all load and line
conditions. Internal loop compensation terminates the
transconductance voltage error amplifier output. For
fixed voltage versions, the error amplifier reference volt-
age is internally set to program the converter output
voltage. For the adjustable output, the error amplifier
reference is fixed at 0.6V.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
activation.
Soft Start / Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1146 into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Input Capacitor
Applications Information
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 volt-
age and is a maximum when VIN is double the output
voltage.
Inductor Selection
The step-down converter uses peak current mode con-
trol 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 AAT1146 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.
VO
VIN
⎛
VO ⎞
VIN ⎠
· 1 -
⎝
CIN =
⎛ VPP
⎝ IO
⎞
- ESR ·FS
⎠
VO
VIN
⎛
VO ⎞
VIN ⎠
1
· 1 -
=
for VIN = 2 × VO
⎝
4
0.75 ⋅ VO 0.75 ⋅ 1.5V
= 0.24
A
m =
=
L
4.7μH
μsec
1
CIN(MIN)
=
⎛ VPP
⎝ IO
⎞
⎠
- ESR · 4 · FS
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed versions. When
externally programming the 0.6V version to 2.5V, the
calculated inductance is 7.5μH.
Always examine the ceramic capacitor DC voltage coef-
ficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 6.3V, X5R
ceramic capacitor with 5.0V DC applied is actually about
6μF.
0.75 ⋅ VO
0.75
⋅
VO
A
μsec
A
L =
=
≈
3
⋅ VO
m
0.24A
μsec
μsec
Configuration
Output Voltage
Inductor
= 3
⋅ 2.5V = 7.5μH
A
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
0.6V to 3.3V
2.2μH
4.7μH
6.8μH
4.7μH
0.6V Adjustable With
External Feedback
In this case, a standard 6.8μH value is selected.
Fixed Output
For high-voltage fixed versions (≥2.5V), m = 0.48A/
μsec. Table 1 displays inductor values for the AAT1146
fixed and adjustable options.
Table 1: Inductor Values.
The maximum input capacitor RMS current is:
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 satura-
tion 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.
VO
VIN
⎛
VO ⎞
VIN ⎠
IRMS = IO ·
· 1 -
⎝
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.
VO
VIN
⎛
VO ⎞
VIN ⎠
1
2
D · (1 - D) = 0.52 =
The 4.7μH CDRH3D16 series inductor selected from
Sumida has a 105mΩ DCR and a 900mA DC current rat-
ing. At full load, the inductor DC loss is 17mW which gives
a 2.8% loss in efficiency for a 400mA, 1.5V output.
· 1 -
⎝
=
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PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
for VIN = 2 · VO
Output Capacitor
The output capacitor limits the output ripple and pro-
vides 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 charac-
teristics necessary for low output ripple.
IO
2
IRMS(MAX)
=
VO
VIN
⎛
VO
1 -
⎞
⎠
·
⎝
VIN
The term
appears in both the input voltage rip-
ple and input capacitor RMS current equations and 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 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. Within two or three switching
cycles, the loop responds and the inductor current
increases to match the load current demand. The rela-
tionship of the output voltage droop during the three
switching cycles to the output capacitance can be esti-
mated by:
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT1146. Low
ESR/ESL X7R and X5R ceramic capacitors are ideal for
this function. To minimize 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 (C2) can be
seen in the evaluation board layout in Figure 2.
3 · ΔILOAD
=
COUT
V
DROOP · FS
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evalu-
ation 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 dur-
ing load transients. Errors in the loop phase and gain
measurements can also result.
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion 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 capac-
itance will reduce the crossover frequency with greater
phase margin.
Since the inductance of a short PCB trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most applications do not
exhibit this problem.
The maximum output capacitor RMS ripple current is
given by:
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
1
V
OUT · (VIN(MAX) - VOUT
)
IRMS(MAX)
=
·
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.
w w w . a n a l o g i c t e c h . c o m
12
1146.2008.06.1.6
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Figure 2: AAT1146 Evaluation Board
Top Side Layout.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1146 Evaluation Board
Bottom Side Layout.
R2 set to either 59kΩ for good noise immunity or 221kΩ
for reduced no load input current.
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage,
the 0.6V version can be externally programmed. Resistors
R1 and R2 of Figure 5 program the output to regulate at
a voltage higher than 0.6V. To limit the bias current
required for the external feedback resistor string while
maintaining good noise immunity, the minimum sug-
gested value for R2 is 59kΩ. Although a larger value will
further reduce quiescent current, it will also increase the
impedance of the feedback node, making it more sensi-
tive to external noise and interference. Table 2 summa-
rizes the resistor values for various output voltages with
V
V
1.5V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
⎠
R1 =
OUT -1 · R2 =
- 1 · 59kΩ = 88.5kΩ
⎠
REF
The adjustable version of the AAT1146, combined with
an external feedforward capacitor (C4 in Figure 5),
delivers enhanced transient response for extreme pulsed
load applications. The addition of the feedforward capac-
itor typically requires a larger output capacitor C1 for
stability.
w w w . a n a l o g i c t e c h . c o m
1146.2008.06.1.6
13
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
switching devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the losses is
given by:
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ
VOUT (V)
R1
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
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO])
PTOTAL
=
VIN
+ (tsw · F · IO + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down con-
verter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
PTOTAL = IO2 · RDSON(HS) + IQ · VIN
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
Thermal Calculations
There are three types of losses associated with the
AAT1146 step-down converter: switching losses, con-
duction 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
Given the total losses, the maximum junction tempera-
ture can be derived from the θJA for the SC70JW-8 pack-
age which is 160°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
1
2
3
Enable
VIN
C4
100pF
U1
AAT1146
1
2
3
4
8
7
6
5
EN
PGND
VOUT =1.8V
R1
118k
4.7μH
OUT PGND
L1
VIN
LX
PGND
AGND
C1
R2
10μF
C2
4.7μF
C3
n/a
59k
GND
LX
GND2
U1 AAT1146 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
Figure 5: AAT1146 Adjustable Version Evaluation Board Schematic
(for Fixed Version, R1 is a short and C4, R2 are open).
w w w . a n a l o g i c t e c h . c o m
14
1146.2008.06.1.6
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
A high density, small footprint layout can be achieved
using an inexpensive, miniature, non-shielded, high DCR
inductor. An evaluation board is available with this induc-
tor and is shown in Figure 6. The total solution footprint
area is 40mm2.
Layout
The suggested PCB layout for the AAT1146 is shown in
Figures 2, 3, and 4. The following guidelines should be
used to help ensure a proper layout.
1. The input capacitor (C2) should connect as closely as
possible to VIN (Pin 3) and PGND (Pins 6-8).
2. C1 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin should be as
short as possible.
3. The feedback trace or OUT pin (Pin 2) should be
separate from any power trace and connect as close-
ly as possible to the load point. Sensing along a
high-current load trace will degrade DC load regula-
tion. If external feedback resistors are used, they
should be placed as closely as possible to the OUT
pin (Pin 2) to minimize the length of the high imped-
ance feedback trace.
4. The resistance of the trace from the load return to
the PGND (Pins 6-8) 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.
Figure 6: Minimum Footprint Evaluation Board
Using 2.0mm x 1.6mm x 0.95mm Inductor.
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1146.2008.06.1.6
15
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO =1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN =2.7V to 4.2V (3.6V nominal)
FS =1.4MHz
TAMB=85°C
1.8V Output Inductor
μsec
A
μsec
A
L1 = 3
⋅ VO2 = 3
⋅ 1.8V = 5.4μH (use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
⎛
⎞
⎠
VO
L1 ⋅ F
VO
VIN
1.8
V
1.8V
4.2V
⎛
⋅ 1 -
⎝
⎞
⎠
ΔIL1 =
=
⋅ 1 -
= 156mA
⎝
4.7µH ⋅ 1.4MHz
ΔIL1
2
IPKL1 = IO +
= 0.4A + 0.068A = 0.468A
2
PL1 = IO ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 6.4μF; use 10µF
0.1V · 1.4MHz
(VO) · (VIN(MAX) - VO)
L1 · F · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 45mArms
IRMS
=
·
=
4.7μH · 1.4MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 3.11μF; use 4.7μF
⎛ VPP
⎝ IO
⎞
⎛ 25mV
⎝ 0.4A
⎞
⎠
- ESR · 4 · FS
- 5mΩ · 4 · 1.4MHz
⎠
IO
IRMS
=
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
w w w . a n a l o g i c t e c h . c o m
16
1146.2008.06.1.6
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
AAT1146 Losses
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
PTOTAL
=
VIN
+ (tsw · F · IO + IQ) · VIN
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
=
+ (5ns · 1.4MHz · 0.4A + 70μA) · 4.2V = 126mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 126mW = 105.1°C
w w w . a n a l o g i c t e c h . c o m
1146.2008.06.1.6
17
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Adjustable Version
(0.6V device)
VOUT (V)
R2 = 59kΩ
R1 (kΩ)
R2 = 221kΩ1
R1 (kΩ)
L1 (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
1.5
1.5
1.5
1.5
1.5
2.2
4.7
4.7
4.7
4.7
6.8
6.8
6.8
Fixed Version
VOUT (V)
R2, R4 Not Used
R1 (kΩ)
L1 (μH)
0.6-3.3V
0
1.5 - 6.8
Table 3: Evaluation Board Component Values.
Max DC
Current (A)
Size (mm)
LxWxH
Manufacturer
Part Number
Inductance (μH)
DCR (Ω)
Type
Sumida
Sumida
Sumida
Murata
Murata
Coilcraft
Coiltronics
Coiltronics
Coiltronics
CDRH3D16-2R2
CDRH3D16-4R7
CDRH3D16-6R8
LQH2MCN4R7M02
LQH32CN4R7M23
LPO3310-472
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
SD3118-4R7
SD3118-6R8
SDRC10-4R7
Table 4: Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
Murata
Murata
Murata
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7μF
10μF
22μF
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.
w w w . a n a l o g i c t e c h . c o m
18
1146.2008.06.1.6
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
Adj ≥ 0.6
1.0
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SOT23-5
OXXYY
4SXYY
1JXYY
1KXYY
1CXYY
QMXYY
AAT1146IJS-0.6-T1
AAT1146IJS-1.0-T1
AAT1146IJS-1.2-T1
AAT1146IJS-1.3-T1
AAT1146IJS-1.8-T1
AAT1146IJS-1.875-T1
AAT1146IGV-0.6-T1
1.2
1.3
1.8
1.875
Adj ≥ 0.6
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/about/quality.aspx.
Package Information
SC70JW-8
0.50 BSC 0.50 BSC 0.50 BSC
0.225 0.075
2.00 0.20
0.048REF
0.100
0.45 0.10
4° 4°
7° 3°
2.10 0.30
All dimensions in millimeters.
1. Contact Sales for other voltage options.
2. XYY = assembly and date code.
3. Sample stock is typically held on part numbers listed in BOLD.
w w w . a n a l o g i c t e c h . c o m
1146.2008.06.1.6
19
PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
SOT23-5
2.85 0.15
1.90 BSC
0.95
BSC
0.60 REF
0.15 0.07
GAUGE PLANE
0.075 0.075
0.45 0.15
0.10 BSC
0.60 REF
10° 5°
0.40 0.10
All dimensions in millimeters.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual
property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
w w w . a n a l o g i c t e c h . c o m
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1146.2008.06.1.6
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