AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1141.2008.07.1.4 1
www.analogictech.com
General Description
The AAT1141 SwitchReg is a 2MHz step-down converter
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.
The AAT1141 is available in fixed voltage versions with
internal feedback and a programmable version with
external feedback resistors. It can deliver 600mA of load
current while maintaining a low 35μA no load quiescent
current. The 2MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
The AAT1141 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
The AAT1141 is available in a Pb-free SOT23-5 package
and is rated over the -40°C to +85°C temperature
range.
Features
• VIN Range: 2.7V to 5.5V
• VOUT Fixed or Adjustable from 0.6V to VIN
• 35μA No Load Quiescent Current
• Up to 98% Efficiency
• 600mA Max Output Current
• 2MHz Switching Frequency
• 150μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• SOT23-5 Package
• Temperature Range: -40°C to +85°C
Applications
• Cellular Phones
• Digital Cameras
• Handheld Instruments
• Microprocessor / DSP Core / IO Power
• PDAs and Handheld Computers
• USB Devices
Typical Application (Fixed Output Voltage)
4.7µH
L1
4.7µF
C1
4.7µF
C2 EN OUT
IN LX
GND
AAT1141
U1
VIN VOUT
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
2 1141.2008.07.1.4
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Pin Descriptions
Pin # Symbol Function
1 IN Input supply voltage for the converter.
2 GND Ground pin. Connect to the output and input capacitor return.
3 EN Enable pin.
4 OUT Feedback input pin. This pin is connected either directly to the converter output or to an external
resistive divider for an adjustable output.
5LX
Switching node. Connect the inductor to this pin. It is internally connected to the drains of both
high- and low-side MOSFETs.
Pin Configuration
SOT23-5
(Top View)
GND
LX
OUT
EN
IN
1
2
34
5
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1141.2008.07.1.4 3
www.analogictech.com
Absolute Maximum Ratings1
Symbol Description Value Units
VIN Input Voltage to GND 6.0 V
VLX LX to GND -0.3 to VIN + 0.3 V
VOUT OUT to GND -0.3 to VIN + 0.3 V
VEN EN to GND -0.3 to 6.0 V
TJOperating Junction Temperature Range -40 to 150 °C
TSStorage Temperature Range -65 to 150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C
Thermal Information
Symbol Description Value Units
PDMaximum Power Dissipation2, 3 667 mW
θJA Thermal Resistance2150 °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. Derate 6.67mW/°C above 25°C.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
4 1141.2008.07.1.4
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Electrical Characteristics1
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol Description Conditions Min Typ Max Units
Step-Down Converter
VIN Input Voltage 2.7 5.5 V
VUVLO UVLO Threshold
VIN Rising 2.7 V
Hysteresis 100 mV
VIN Falling 1.8 V
VOUT Output Voltage Tolerance IOUT = 0 to 600mA, VIN = 2.7V to 5.5V -3.5 +3.5 %
VOUT Output Voltage Range 0.6 VIN V
IQQuiescent Current No Load, 0.6V Adjustable Version 35 70 μA
ISHDN Shutdown Current EN = AGND = PGND 1.0 μA
ILIM P-Channel Current Limit 800 mA
RDS(ON)H High Side Switch On Resistance 0.35 Ω
RDS(ON)L Low Side Switch On Resistance 0.30 Ω
ILXLEAK LX Leakage Current VIN = 5.5V, VLX = 0 to VIN, EN = GND 1 μA
ΔVLinereg Line Regulation VIN = 2.7V to 5.5V 0.1 %/V
VOUT Out Threshold Voltage Accuracy 0.6V Output, No Load, TA = 25°C 588 600 612 mV
IOUT Out Leakage Current 0.6V Output 0.2 μA
ROUT Out Impedance >0.6V Output 250 kΩ
TSStart-Up Time From Enable to Output Regulation 150 μs
FOSC Oscillator Frequency TA = 25°C 1.2 2.0 2.6 MHz
TSD Over-Temperature Shutdown Threshold 140 °C
THYS Over-Temperature Shutdown Hysteresis 15 °C
EN
VEN(L) Enable Threshold Low 0.6 V
VEN(H) Enable Threshold High 1.4 V
IEN Input Low Current VIN = VOUT = 5.5V -1.0 1.0 μA
1. The AAT1141 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.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1141.2008.07.1.4 5
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
1141.2008.07.1.4 5
www.analogictech.com
Typical Characteristics
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8µ
µ
H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
DC Regulation
(VOUT = 3.3V; L = 6.8µH)
Output Current (mA)
Output Error (%)
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
0 100 200 300 400 500 60
0
VIN = 4.2V VIN = 5.0V
VIN = 5.5V
Efficiency vs. Load
(VOUT = 2.5V; L = 6.8µ
µ
H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1 1 10 100 1000
VIN = 5.0V
VIN = 3.6V
VIN = 4.2V
VIN = 2.7V
DC Regulation
(VOUT = 2.5V; L = 6.8µH)
Output Current (mA)
Output Error (%)
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
0 100 200 300 400 500 600
VIN = 3.0V VIN = 3.6V VIN = 4.2V
VIN = 5.0V
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7µ
µ
H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1 1 10 100 100
0
VIN = 2.7V
VIN = 3.6V VIN = 4.2V
DC Regulation
(VOUT = 1.8V; L = 4.7μH)
Output Current (mA)
Output Error (%)
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
0 100 200 300 400 500 60
0
VIN = 2.7V VIN = 3.6V
VIN = 4.2V
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Typical Characteristics
Soft Start
(VIN = 3.6V; VOUT = 1.8V; Load = 3Ω; CFF = 100pF)
Time (100μs/div)
VOUT
(2V/div)
EN
(2V/div)
IIN
(200mA/div)
0mA
0V
0V
Line Regulation
(VOUT = 1.8V)
Input Voltage (V)
Output Voltage (V)
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
IOUT = 10mA
IOUT = 600mA
Output Voltage Error vs. Temperature
(V
IN
= 3.6V; V
O
= 1.8V; I
OUT
= 400mA)
Temperature (°
°
C)
-2.0
-1.0
0.0
1.0
2.0
-40 -20 0 20 40 60 80 100
Output Error (%)
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
Temperature (°
°
C)
Frequency Variation (%)
-40 -20 0 20 40 60 80 100
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
8.00
10.00
Frequency vs. Input Voltage
Input Voltage (V)
Frequency Variation (%)
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.
5
VOUT = 1.8V
VOUT = 2.5V VOUT = 3.3V
No Load Quiescent Current vs. Input Voltage
(VOUT = 3.0V, L = 6.8µH)
Input Voltage (V)
Supply Current (µA)
20
25
30
35
40
45
50
55
60
3.3 3.8 4.3 4.8 5.3
TA = 85°C
TA = 25°C
TA = -40°C
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Typical Characteristics
No Load Quiescent Current vs. Input Voltage
(VOUT = 1.8V, L = 4.7µH)
Input Voltage (V)
Supply Current (mA)
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
TA = 85°C
TA = 25°C
TA = -40°C
No Load Quiescent Current vs. Input Voltage
(VOUT = 1.2V, L = 2.2µH)
Input Voltage (V)
Supply Current (mA)
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
TA = 85°C
TA = -40°C
TA = 25°C
P-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON)H (mΩ
)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
100
200
300
400
500
600
700
85°C
25°C
-40°C
N-Channel RDS(ON) vs. Input Voltage
Input Voltage (V)
RDS(ON)L (mΩ
Ω
)
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
100
150
200
250
300
350
400
450
500
550
600
85°C
25°C
-40°C
Step-Down Converter Load Transient Response
(1mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
COUT = 4.7µF; CFF = 100pF)
Time (40µs/div)
VOUT
(100mV/div)
IOUT
(100mA/div)
300mA
1mA
1.8V
Step-Down Converter Load Transient Response
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.8V; COUT = 4.7µF; CFF = 100pF)
Time (40µs/div)
VOUT
(50mV/div)
IOUT
(100mA/div)
400mA
300mA
1.8V
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
8 1141.2008.07.1.4
www.analogictech.com
Typical Characteristics
Step-Down Converter Load Transient Response
(1mA to 300mA; VIN = 3.6V; VOUT = 1.0V;
COUT = 10µF; CFF = 0pF)
Time (40µs/div)
VOUT
(100mV/div)
IOUT
(100mA/div)
300mA
1.0V
1mA
Step-Down Converter Load Transient Response
(300mA to 400mA; VIN = 3.6V;
VOUT = 1.0V; COUT = 10µF; CFF = 0pF)
Time (40µs/div)
VOUT
(50mV/div)
IOUT
(100mA/div)
400mA
1.0V
300mA
Line Response
(VOUT = 1.8V @ 400mA)
Output Voltage
(top) (V)
Input Voltage
(bottom) (V)
Time (25μ
μ
s/div)
1.76
1.77
1.78
1.79
1.80
1.81
1.82
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Step-Down Converter Output Ripple
(VOUT = 1.8V; VIN = 3.6V; IOUT = 1mA; L = 4.7µH;
CFF = 100pF; COUT = 4.7µF)
Time (10µs/div)
Output
Ripple
(20mV/div)
LX
(2V/div)
Inductor
Current
(100mA/div)
0mA
1.8V
1.8V
Step-Down Converter Output Ripple
(VOUT = 1.8V; VIN = 3.6V; IOUT = 600mA;
L = 4.7µH; CFF = 100pF; COUT = 4.7µF)
Time (0.5µs/div)
Output
Ripple
(20mV/div)
LX
(2V/div)
Inductor
Current
(100mA/div)
600mA
0V
1.8V
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Functional Description
The AAT1141 is a high performance 600mA 2MHz mono-
lithic step-down converter. It has been designed with the
goal of minimizing external component size and optimiz-
ing 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 recommended (see table
of values).
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-
tional feed-forward capacitor can also be added to the
external feedback to provide improved transient response
(see Figure 1).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the RDS(ON) 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 600mA.
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.
Functional Block Diagram
EN
LX
Err
.
Amp
Logic
DH
DL
GND
IN
OUT
Voltage
Reference
INPUT
See note
Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly
to the internal error amplifier.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Control Loop
The AAT1141 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.
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.
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 AAT1141 into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
Current Limit and
Over-Temperature Protection
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.
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
condition is removed, the output voltage automatically
recovers.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the IN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
activation.
IN
1LX 5
GND
2
EN
3OUT 4
U1
1
2
3
C1
4.7μF
L1
4.7μH
SW
VOUT
AAT1141
C2
4.7μF
C3
100pF R1
118k
R2
59k
VIN
Enable
Figure 1: Enhanced Transient Response Schematic.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Applications Information
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 AAT1141 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 · V
O
m = = = 0.24
L
0.75 · 1.5V
4.7μH
A
μs
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.
0.75 · V
O
L = =
≈
3 · V
O
= 3 · 2.5V = 7.5μH
m
0.75 · V
O
0.24
μs
A
μs
A
A
μs
In this case, a standard 6.8μH value is selected.
For high-voltage fixed versions (≥2.5V), m = 0.48A/
μsec. Table 1 displays inductor values for the AAT1141
fixed and adjustable options.
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.
The 4.7μH CDRH2D14 series inductor selected from
Sumida has a 135mΩ typical DCR and a 1A DC current
rating. At full load, the inductor DC loss is 48mW which
gives a 4.5% loss in efficiency for a 600mA, 1.8V output.
Output
Voltage (V) Inductor (μH)
Output
Capacitor (μF)
1, 1.2 2.2 10
1.5, 1.8 4.7 4.7
2.5, 3.3 6.8 4.7
Table 1: Inductor and Output Capacitor Values.
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.
⎛⎞
· 1 -
⎝⎠
VO
VIN
CIN =
VO
VIN
⎛⎞
- ESR · FS
⎝⎠
VPP
IO
⎛⎞
· 1 - = for VIN = 2 · V
O
⎝⎠
VO
VIN
VO
VIN
1
4
CIN(MIN) = 1
⎛⎞
- ESR · 4 · FS
⎝⎠
VPP
IO
Always examine the ceramic capacitor DC voltage coeffi-
cient 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.
The maximum input capacitor RMS current is:
⎛⎞
IRMS = IO · · 1 -
⎝⎠
VO
VIN
VO
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.
⎛⎞
· 1 - = D · (1 - D) = 0.52 =
⎝⎠
VO
VIN
VO
VIN
1
2
for VIN = 2 · VO
IO
RMS(MAX)
I2
=
The term
⎛⎞
· 1 -
⎝⎠
VO
VIN
VO
VIN appears in both the input voltage
ripple and input capacitor RMS current equations and is
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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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 AAT1141. 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.
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.
Figure 2: AAT1141 Sample Layout Figure 3: Exploded View of Sample Layout.
Top Side.
Figure 4: AAT1141 Sample Layout
Bottom Side.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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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.
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.
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.
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:
COUT =
3 · ΔILOAD
VDROOP · FS
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.
The maximum output capacitor RMS ripple current is
given by:
1
23
VOUT · (VIN(MAX) - VOUT)
RMS(MAX)
IL · 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 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
R2 set to either 59kΩ for good noise immunity or 316kΩ
for reduced no load input current.
⎛⎞
⎝⎠
R1 = -1 · R2 = - 1 · 59kΩ = 88.5kΩ
VOUT
VREF
⎛⎞
⎝⎠
1.5V
0.6V
The adjustable version of the AAT1141, combined with
an external feedforward capacitor (C3 in Figure 1),
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.
VOUT (V)
High Noise
Immunity
R2 = 59kΩ
R1 (kΩ)
Low Input
Current
(Without Load)
R2 = 316kΩ
R1 (kΩ)
0.8 19.6 105
0.9 29.4 158
1.0 39.2 210
1.1 49.9 267
1.2 59.0 316
1.3 68.1 365
1.4 78.7 422
1.5 88.7 475
1.8 88.7 634
2.0 137 732
2.5 187 1000
3.0 237 1270
3.3 267 1430
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
14 1141.2008.07.1.4
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Thermal Calculations
There are three types of losses associated with the
AAT1141 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
switching devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the LDO losses
is given by:
PTOTAL
IO
2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO])
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:
PTOTAL = IO
2 · 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.
Given the total losses, the maximum junction tempera-
ture can be derived from the θJA for the SOT23-5 pack-
age which is 150°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Output Dropout
At dropout, the duty cycle of AAT1141 switching is
100%. The minimum dropout voltage is determined by
RDS(ON)H and the inductor copper loss resistor. AAT1141
has 0.35Ω RDS(ON)H. The inductor copper loss resistor var-
ies with different inductor values and manufacturer. The
safe dropout voltage is 0.5V for a 600mA load.
For example, when load current is 600mA, the voltage
dropped across RDS(ON)H is 0.21V; if the inductor copper
loss resistor is 135mΩ, the voltage drop across the
inductor is 0.08V. So the total voltage drop is 0.29V.
Considering manufacturer’s tolerances, the inductor cop-
per loss resistor and RDS(ON)H will vary from part to part,
a 0.4V dropout window is safe.
IN
1LX 5
GND
2
EN
3OUT 4
U1
1
2
3
C1
4.7μF
L1
4.7μH
SW
V = 1.8V
OUT
AAT1141
C2
4.7μF
C3
100pF R1
634k
R2
316k
VIN
Enable
Figure 5: AAT1141 Adjustable Evaluation Board Schematic.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Efficiency
Besides the AAT1141 device losses including switching
losses, conduction losses, and quiescent current losses,
the inductor copper loss also affects the efficiency of the
buck converter. To the buck converter, the average cur-
rent of the inductor is equal to output current IO. So the
loss in the inductor is:
PLOSS_L = IO2 · RL
Table 4 shows some recommended inductors. A larger size
inductor usually has smaller DCR. As a example: if select-
ing CDRH2D14 4.7μH for 1.8V output, the PLoss_L is 48.6mW
when output current is 600mA, so the inductor loses 4.5%
power; if selecting CDRH3D23 4.7μH, the PLoss_L should be
19.8mW, and the inductor losing power ratio is only 1.8%.
The inductor size and the buck converter efficiency is
always a trade-off in the real application.
Layout
The suggested 2-layer PCB layout for the AAT1141 is
shown in Figures 2, 3 and 4. The following guide lines
should be used to help ensure a proper layout.
1. The power traces (GND, LX, VIN) should be kept
short, direct, and wide to allow large current flow.
Place sufficient multiple-layer pads when needed to
change the trace layer.
2. The input capacitor (C1) should connect as closely
as possible to IN and GND.
3. The output capacitor C2 and L1 should be connected
as closely as possible. The connection of L1 to the LX
pin should be as short as possible and there should
not be any signal lines under the inductor.
4.
The feedback trace or OUT pin should be separate
from any power trace and connect as closely as pos-
sible 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 OUT pin to minimize the
length of the high impedance feedback trace.
5. 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 differ-
ences in the potential of the internal signal ground
and the power ground.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
16 1141.2008.07.1.4
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
16 1141.2008.07.1.4
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Step-Down Converter Design Example
Specifications
VO = 1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 2MHz
TAMB = 85°C
1.8V Output Inductor
L1 = 3 · V
O2
= 3 · 1.8V = 5.4µH
µs
A
µs
A
(use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
V
O
V
O
1.8
V
1.8V
ΔI
L1
= · 1 - = · 1 - = 109.2m
A
L1 · F
V
IN
4.7µH · 2MHz
4.2V
I
PKL1
= I
O
+ ΔI
L1
= 0.6A + 0.055A = 0.655A
2
P
L1
= I
O
2
· DCR = 0.6A
2
· 105mΩ = 38mW
1.8V Output Capacitor
VDROOP = 0.1V
1
23
1 1.8V · (4.2V - 1.8V)
4.7µH · 2MHz · 4.2V
23
RMS
IL1 · F · VIN(MAX)
= ·
·
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.1V · 2MHz
COUT = = = 4.48µF; use 10µF
· = 31.5mArms
·
(VO) · (VIN(MAX) - VO)=
Pesr = esr · IRMS2 = 5mΩ · (31.5mA)2 = 5µW
Input Capacitor
Input Ripple VPP = 25mV
CIN = = = 3.4µF; use 4.7µF
1
- ESR · 4 · FS
VPP
IO
1
- 5mW · 4 · 2MHz
25mV
0.6A
IO
RMS
I
P = esr · IRMS
2 = 5mΩ · (0.3A)2 = 0.45mW
2
= = 0.3Arms
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141 Losses
PTOTAL
+ (tsw · F · IO + IQ) · VIN
IO
2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
VIN
=
=
+ (5ns · 2MHz · 0.6A + 70μA) · 4.2V = 141mW
0.62 · (0.35Ω · 1.8V + 0.3Ω · [4.2V - 1.8V])
4.2V
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (150°C/W) · 141mW = 106.2°C
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
18 1141.2008.07.1.4
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Adjustable Version
(0.6V device)
VOUT (V)
R2 = 59kΩ
R1 (kΩ)
R2 = 316kΩ1
R1 (kΩ) L1 (μH)
0.8 19.6 105 2.2
0.9 29.4 158 2.2
1.0 39.2 210 2.2
1.1 49.9 267 2.2
1.2 59.0 316 2.2
1.3 68.1 365 2.2
1.4 78.7 422 4.7
1.5 88.7 475 4.7
1.8 118 634 4.7
1.85 124 732 4.7
2.0 137 1000 6.8
2.5 187 1270 6.8
3.3 267 1430 6.8
Fixed Version
VOUT (V)
R2 Not Used
R1 (kΩ) L1 (μH)
0.6-3.3V 0 4.7
Table 3: Evaluation Board Component Values.
Manufacturer Part Number Inductance (μH)
Max DC
Current (A) DCR (Ω)
Size (mm)
LxWxH Type
Sumida CDRH3D16-2R2 2.2 1.20 0.072 3.8x3.8x1.8 Shielded
Sumida CDRH3D16-4R7 4.7 0.90 0.105 3.8x3.8x1.8 Shielded
Sumida CDRH3D16-6R8 6.8 0.73 0.170 3.8x3.8x1.8 Shielded
Sumida CDRH2D14
2.2 1.5 75
3.2x3.2x1.55 Shielded4.7 1.0 135
6.8 0.85 170
Murata LQH2MCN4R7M02 4.7 0.40 0.80 2.0x1.6x0.95 Non-Shielded
Murata LQH32CN4R7M23 4.7 0.45 0.20 2.5x3.2x2.0 Non-Shielded
Coilcraft LPO3310-472 4.7 0.80 0.27 3.2x3.2x1.0 1mm
Coiltronics SD3118-4R7 4.7 0.98 0.122 3.1x3.1x1.85 Shielded
Coiltronics SD3118-6R8 6.8 0.82 0.175 3.1x3.1x1.85 Shielded
Coiltronics SDRC10-4R7 4.7 1.30 0.122 5.7x4.4x1.0 1mm Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer Part Number Value Voltage Temp. Co. Case
Murata GRM219R61A475KE19 4.7μF 10V X5R 0805
Murata GRM21BR60J106KE19 10μF 6.3V X5R 0805
Murata GRM21BR60J226ME39 22μF 6.3V X5R 0805
Table 5: Surface Mount Capacitors.
1. For reduced quiescent current, R2 = 316kΩ.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Ordering Information
Output Voltage1Package Marking2Part Number (Tape and Reel)3
Adj 0.6 to VIN TSOT23-5 YJXYY AAT1141ICB-0.6-T1
Adj 0.6 to VIN SOT23-5 1AXYY AAT1141IGV-0.6-T1
1.0 SOT23-5 5AXYY AAT1141IGV-1.0-T1
1.2 SOT23-5 4VXYY AAT1141IGV-1.2-T1
1.5 SOT23-5 5BXYY AAT1141IGV-1.5-T1
1.8 SOT23-5 ZEXYY AAT1141IGV-1.8-T1
3.0 SOT23-5 5CXYY AAT1141IGV-3.0-T1
3.3 SOT23-5 5DXYY AAT1141IGV-3.3-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/about/quality.aspx.
Package Information
SOT23-5
4
°
±
4
°
0.15
±
0.07
0.45
±
0.15 0.10 BSC
1.20
±
0.25
1.575
±
0.125
2.80
±
0.20
0.40
±
0.10
0.60 REF
2.85
±
0.15
1.90 BSC
0.95
BSC
1.10
±
0.20
10
°
±
5
°
GAUGE PLANE
0.075
±
0.075
0.60 REF
All dimensions in millimeters.
1. Contact Sales for other voltage options.
2. XYY = assembly and date code.
3. Sample stock is generally held on part numbers listed in BOLD.
AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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AAT1141
Fast Transient 600mA Step-Down ConverterSwitchRegTM
PRODUCT DATASHEET
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Phone (408) 737-4600
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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 specifi cations or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
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support this warranty. Specifi c 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.
TSOT23-5
0.450
±
0.150 0.950 BSC
1.600 BSC
0.450
±
0.150
0.127 BSC
Detail "A"
2.800 BSC
1.900 BSC
0°
+
10°
-0°
Top View
End View
Detail "A"
Side View
0.950
±
0.150
0.050
±
0.050
2.900 BSC
All dimensions in millimeters.
Disposition / Action to be done:
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Form#: FM-QA-001 Rev. 01