SwitchReg
TM
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
1
General Description
The AAT1154 SwitchRegTM is a member of
AnalogicTechTM's Total Power ManagementTM IC
product family. The Step-down switching converter
is ideal for applications where high efficiency, small
size, and low ripple are critical. Able to deliver 3A
with an internal power MOSFET, the current-mode
controlled IC provides high efficiency. Fully inter-
nally compensated, the AAT1154 simplifies system
design and lowers external part count.
The AAT1154 is available in an SOP-8 package,
rated over -40 to 85C.
Features
V
IN
Range: 2.7-5.5Volts
Fixed or adjustable V
OUT
: 1.0V - 4.2V
3A output current
Up to 95% efficiency
Integrated low on resistance power switch
Internally compensated current mode control
1MHz switching frequency
Fixed or adjustable V
OUT
: 1.0 to 4.2V
Constant PWM mode
Low output ripple with light load
Internal softstart
Current limit protection
Over-Temperature protection
SOP-8 package
-40 to 85C Temperature Range
Applications
Computer Peripherals
Set Top Boxes
Network Cards
Cable/DSL Modems
High efficiency conversion from 5V or 3.3V
supply
Typical Application
OUTPUT
INPUT
1.5
H
120
F
LX
V
P
FB
GND
AAT1154
V
CC
ENABLE
10
F
0.1
F
100
AAT1154
1MHz 3A Buck DC/DC Converter
2
1154.2004.08.1.2
Pin Descriptions
Pin Configuration
SO-8
1
2
LX
V
P
LX
V
P
FB
GND
EN
V
CC
1
2
3
4
8
7
6
5
Pin #
Symbol
Function
1
FB
Feedback input pin. This pin must be connected to the converter's
output. It is used to set the output of the converter to regulate to the
desired value.
2
GND
Ground connection.
3
EN
Enable input pin. When connected high, AAT1154 is in normal
operation. When connected low, it is powered down. This pin
should not be left floating.
4
VCC
Power supply. It supplies power for the internal circuitry.
5, 8
VP
Input Supply Voltage for converter power stage.
6, 7
LX
Inductor connection pins. These pins should be connected to the
output inductor. Internally, pins 6 & 7 are connected to the drain of
the P-channel switch.
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
3
Absolute Maximum Ratings
(T
A
=25C unless otherwise noted)
Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at con-
ditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time.
Note 1: Human body model is a 100pF capacitor discharged through a 1.5K resistor into each pin.
Thermal Characteristics
Note 2: Mounted on a demo board (FR4, in still air).
Note 3: Derate 9.1mW/C above 25C.
Recommended Operating Conditions
Symbol
Description
Rating
Units
T
Ambient Temperature Range
-40 to +85
C
Symbol
Description
Value
Units
JA
Thermal Resistance
2
110
C/W
P
D
Maximum Power Dissipation (T
A
= 25C)
2, 3
909
mW
Symbol
Description
Value
Units
V
CC
, V
P
V
CC
, V
P
to GND
6
V
V
LX
LX to GND
-0.3 to V
P
+0.3
V
V
FB
FB to GND
-0.3 to V
CC
+0.3
V
V
EN
EN to GND
-0.3 to V
CC
+0.3
V
T
J
Operating Junction Temperature Range
-40 to 150
C
V
ESD
ESD Rating
1
- HBM
3000
V
Electrical Characteristics
(V
IN
= V
CC
= V
P
= 5V, T
A
= -40 to 85C unless otherwise noted. Typical
values are at T
A
= 25C)
Symbol
Description
Conditions
Min Typ Max Units
V
IN
Input Voltage Range
2.7
5.5
V
V
OUT
Output Voltage Tolerance
V
IN
= V
OUT
+ 0.2 to 5.5V,
-5.0
5.0
%
I
OUT
= 0 to 3A
V
UVLO
Under Voltage Lockout
V
IN
Rising
2.5
V
V
IN
Falling
1.2
V
V
UVLO(HYS)
Under Voltage Lockout Hysteresis
250
mV
I
Q
Quiescent Supply Current
No Load, V
FB
= 0 V
630 1000
A
I
SHDN
Shutdown Current
V
EN
= 0 V, V
IN
= 5.5V
1.0
A
I
LIM
Current Limit
T
A
= 25C
4.4
A
R
DS(ON)L
High Side Switch On Resistance
T
A
= 25C
60
m
Efficiency
I
OUT
= 1.0 A
92
V
OUT
(V
OUT
*
V
IN
) Load Regulation
I
LOAD
= 0 - 3A
2.6
%
V
OUT
/V
OUT
Line Regulation
V
IN
= 2.7 to 5.5V
0.75
%/V
F
OSC
Oscillator Frequency
T
A
= 25C
1
MHz
V
EN(L)
Enable Threshold Low
0.6
V
V
EN(H)
Enable Threshold High
1.4
V
T
SD
Over Temp Shutdown Threshold
140
C
T
HYS
Over Temp Shutdown Hysteresis
15
C
AAT1154
1MHz 3A Buck DC/DC Converter
4
1154.2004.08.1.2
Typical Characteristics
Output Voltage vs. Temperature
I
OUT
=2A
-20
0
20
40
60
80
100
Temperature (
C)
Variation (%)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
Enable Threshold vs. Input Voltage
0.6
0.7
0.8
0.9
1
1.1
1.2
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Enable Threshold (V)
EN(H)
EN(L)
Oscillator Frequency Variation vs. Temperature
V
IN
= 5V
-4
-3
-2
-1
0
1
-20
0
20
40
60
80
100
Temperature (
C)
Variation (%)
R
DS(ON)
vs. V
IN
, I
DS
= 1A
40
45
50
55
60
65
70
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
R
DS(ON)
(m
)
Oscillator Frequency Variation vs.
Supply Voltage
-0.5
-0.25
0
0.25
0.5
3.5
4
4.5
5
5.5
Input Voltage (V)
Variation (%)
R
DS(ON)
vs. Temperature
40
50
60
70
80
90
-20
0
20
40
60
80
100
120
Temperature (
C)
R
DS(ON)
(m
)
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
V
IN
= 5.5V
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
5
Typical Characteristics
Inrush and Output Overshoot Characteristic
3A Load
-2
0
2
4
6
8
10
12
14
0
0.4
0.8
1.2
1.6
2
Time (millisec)
Voltage (V)
(bottom traces)
-10
-8
-6
-4
-2
0
2
4
6
Current (A)
(top trace)
Inductor Current
Output
Input
Over Temp Shutdown Current vs. Temperature
V
OUT
= 3.3V, V
IN
= 5.0V, L = 1.5
H
2
2.5
3
3.5
4
4.5
5
5.5
6
10
20
30
40
50
60
70
80
90
100
Temperature (
C)
Output Current (A)
Non-Switching Operating Current vs. Temperature
FB = 0V
0.4
0.5
0.6
0.7
0.8
-20
0
20
40
60
80
100
120
Temperature (
C)
Operating Current (mA)
V
IN
= 5.5V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.0V
Load Regulation
V
IN
= 5.0V, V
IN
= 3.3V
-10.0
-9.0
-8.0
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
0.01
0.1
1
10
Load Current (A)
Output Error (%)
Over Temp Current vs. Input Voltage
V
OUT
= 3.3V
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
3.5
3.75
4
4.25
4.5
4.75
5
5.25
5.5
Input Voltage (V)
Output Current (A)
100C
70C
85C
Line Regulation
V
OUT
=3.3V
-5
-4
-3
-2
-1
0
1
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Output Voltge Error (%)
I
O
= 0.3A
I
O
= 3.0A
AAT1154
1MHz 3A Buck DC/DC Converter
6
1154.2004.08.1.2
Typical Characteristics
Loop Crossover Gain and Phase
-16
-12
-8
-4
0
4
8
12
16
10000
100000
Frequency (Hz)
Gain (dB)
-180
-135
-90
-45
0
45
90
135
180
Phase (Degrees)
120
F 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
Phase
Gain
Loop Crossover Gain and Phase
-16
-12
-8
-4
0
4
8
12
16
10000
100000
Frequency (Hz)
Gain (dB)
-180
-135
-90
-45
0
45
90
135
180
Phase (Degrees)
100
F 6.3V Ceramic
TDK P/N C3225X5R0J107M
Phase
3x 100
F
2x 100
F
Tantalum Output Ripple
I
OUT
= 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
-120
-100
-80
-60
-40
-20
0
20
40
0
1
2
3
4
5
Time (
sec)
AC Output Ripple (top)
(mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
120
F 6.3V Tantalum Vishay
P/N 594D127X96R3C2T
Output Ripple
I
OUT
= 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
-12
-10
-8
-6
-4
-2
0
2
4
0
1
2
3
4
5
AC Output Ripple
(top) (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
Time (
sec)
200 uF 6.3V Ceramic
TDK P/N C3325X5R0J107M
Output Ripple
I
OUT
= 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
-12
-10
-8
-6
-4
-2
0
2
4
0
1
2
3
4
5
Time (
sec)
AC Output Ripple
top (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
bottom (A)
300 F 6.3VCeramic
TDK P/N C3325X5R0J107M
Inrush and Output Overshoot Characteristic
No Load
-2
0
2
4
6
8
10
12
14
0
0.4
0.8
1.2
1.6
2
Time (millisec)
Voltage (V)
(bottom traces)
-10
-8
-6
-4
-2
0
2
4
6
Current (A)
(top trace)
Inductor Current
Output
Input
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
7
AAT1154
1MHz 3A Buck DC/DC Converter
8
1154.2004.08.1.2
Typical Characteristics
Tantalum Transient Response
I
OUT
= 0 to 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
-700
-600
-500
-400
-300
-200
-100
0
100
0
100
200
300
400
500
Time (
s)
Output Voltage
(top) (mV)
-1
0
1
2
3
4
5
6
7
Inductor Current
(bottom) (A)
120
F 6.3V Tantalum
Vishay P/N 594D127X96R3C2T
Transient Response
I
OUT
= 0 to 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
Time (
s)
Output Voltage
(top) (mV)
Inductor Current
(bottom) (A)
-700
-600
-500
-400
-300
-200
-100
0
100
0
100
200
300
400
500
-1
0
1
2
3
4
5
6
7
2x 100 uF 6.3V Ceramic
TDK P/N C3325X5R0J107M
Transient Response
I
OUT
= 0 to 3.0A, V
OUT
= 3.3V, V
IN
= 5.0V
Time (
s)
Output Voltage
(top) (mV)
Inductor Current
(bottom) (A)
-700
-600
-500
-400
-300
-200
-100
0
100
0
100
200
300
400
500
-1
0
1
2
3
4
5
6
7
3x 100
F 6.3V Ceramic
TDK P/N C3325X5R0J107M
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
9
Functional Block Diagram
V
P
= 2.7V- 5.5V
EN
GND
LOGIC
REF
Temp.
Sensing
OSC
OP. AMP
V
CC
LX
FB
DH
CMP
Applications Information
Main Control Loop
The AAT1154 is a peak current mode buck con-
verter. The inner wide bandwidth loop controls the
inductor peak current. The inductor current is
sensed as it flows through the internal P-Channel
MOSFET. A fixed slope compensation signal is
then added to the sensed current to maintain sta-
bility for duty cycles greater than 50%. The inner
loop appears as a voltage programmed current
source in parallel with the output capacitor.
The voltage error amplifier output programs the cur-
rent loop for the necessary inductor current to force
a constant output voltage for all load and line con-
ditions. The feedback resistive divider is internal,
dividing the output voltage to the error amplifier ref-
erence voltage of 1.0V. The error amplifier has a
limited DC gain. This eliminates the need for exter-
nal compensation components while still providing
sufficient DC loop gain for good load regulation.
The crossover frequency and phase margin are set
by the output capacitor value.
Duty cycle extends to 100% as the input voltage
approaches the output voltage. Thermal shutdown
protection disables the device in the event of a
short circuit or overload condition.
Soft Start/Enable
Soft-start controls the current limit when the input
voltage or enable is applied. It limits the current
surge seen at the input and eliminates output volt-
age overshoot.
The enable input, when pulled low, forces the
device into a low power non-switching state. The
total input current during shutdown is less than 1A.
Power and Signal Source
Separate small signal ground and power supply
pins isolate the internal control circuitry from
switching noise. In addition, the low pass filter R1
and C3 in figure 3 filters noise associated with the
power switching.
AAT1154
1MHz 3A Buck DC/DC Converter
10
1154.2004.08.1.2
Current Limit and Over Temp
Protection
The AAT1154 over temp and current limit circuitry
protects the AAT1154 as well as the external
Schottky diode during overload, short circuit and
excessive ambient temperature conditions. The
junction over temp threshold is 140C nominal and
has 15C of hysteresis. Typical graphs of the over
temp load current vs. input voltage and ambient tem-
perature are shown in the Typical Characteristics
section.
Inductor
The output inductor is selected to limit the ripple
current to 20-40% of the full load current at the
maximum input voltage. Manufacturer's specifica-
tions list both the inductor DC current rating, which
is a thermal limitation, and the peak current rating,
which is determined by the inductor saturation
characteristics. The inductor should not show any
appreciable saturation under all normal load condi-
tions. During overload and short circuit conditions
the inductor can exceed its peak current rating
without affecting the converter performance. Some
inductors may have sufficient peak and average
current ratings yet result in excessive losses due to
a high DC resistance (DCR). The losses associat-
ed with the DCR and its affect on the total convert-
er efficiency must be considered.
For a 3 Amp load and the ripple current set to 30%
at the maximum input voltage, the maximum peak
to peak ripple current is 0.9Amp. Assuming a 5V
5% input voltage and 30% ripple the output induc-
tance required is
The factor "k" is the fraction of the full load (30%)
selected for the ripple current at the maximum input
voltage.
The corresponding inductor RMS current is:
I is the peak to peak ripple current which is fixed by
the inductor selection above. For a peak to peak cur-
rent of 30% of the full load current the peak current
at full load will be 115% of the full load. The 1.5H
inductor selected from the Sumida CDRH6D38
series has a 11m
DCR and a 4.0 Amp DC current
rating with a height of 4 mm. At full load the inductor
DC loss is 99 mW for a 1 % loss in efficiency.
Schottky Freewheeling Diode
The Schottky average current is the load current
times one minus the duty cycle. For V
IN
at 5 Volts
and Vout at 3.3 Volts the average diode current is
With a 125C maximum junction temperature and a
120C/W thermal resistance the maximum average
current is
For overload, short circuit, and excessive ambient
conditions the AAT1154 enters the over-tempera-
ture shutdown mode protecting the AAT1154 as well
as the output Schottky. In this mode the output cur-
rent is limited internally until the junction tempera-
ture reaches the temperature limit (see over temp
characteristics graphs). The diode reverse voltage
must be rated to withstand the input voltage.
J(MAX)
AMB
125
70
= 1.14A
120 /
0.4
AVG
T
T
C
C
I
W
V
-
-
=
=
C
J-A
V
FWD
3.3
1
3
1
1
5.0
O
AVG
O
IN
V
V
I
I
A
A
V
V
=
-
=
-
=
2
2
3
12
RMS
O
O
I
I
I
I
A
=
+
=
L = 1 -
V
OUT
V
OUT
I
OUT
k F
SW
V
IN(MAX)
= 1 -
3.3V
3.3V
3.0A 0.3 1MHz
5.25V
= 1.36
H
3 Amp Surface Mount Schottky Diodes
Input Capacitor Selection
The primary function of the input capacitor is to pro-
vide a low impedance loop for the edges of pulsed
current drawn by the AAT1154. A low ESR/ESL
ceramic capacitor is ideal for this function. To mini-
mize the stray inductance the capacitor should be
placed as close as possible to the IC. This also
keeps the high frequency content of the input cur-
rent localized, minimizing the radiated and con-
ducted EMI while facilitating optimum performance
of the AAT1154. The proper placement of the input
capacitor C1 is shown in the layout in figure 1.
Ceramic X5R or X7R capacitors are ideal. The
size required will vary depending on the load, out-
put voltage, and input voltage source impedance
characteristics. Typical values range from 1F to
10 F. The input capacitor RMS current varies with
the input voltage and the output voltage. It is high-
est when the input voltage is double the output volt-
age where it is one half of the load current.
A high ESR tantalum with a value about 10 times
the input ceramic capacitor may also be required
when using a 10F or smaller ceramic input bypass
capacitor. This dampens out any input oscillations
that may occur due to the source inductance res-
onating with the converter input impedance
Output Capacitor
With no external compensation components, the
output capacitor has a strong effect on the loop sta-
bility. Larger output capacitance will reduce the
crossover frequency with greater phase margin. A
200F ceramic capacitor provides sufficient bulk
capacitance to stabilize the output during large load
transitions and has ESR and ESL characteristics
necessary for very low output ripple. The RMS rip-
ple current is given by
For a ceramic output capacitor the dissipation due
to the RMS current and output ripple associated
with are negligible.
Tantalum capacitors, with sufficiently low ESR to
meet output ripple requirements, generally have an
RMS current rating much greater than that actually
seen in this application. The maximum tantalum
output capacitor ESR is
Where
I is the peak to peak inductor ripple current.
Due to the ESR zero associated with the tantalum
capacitor, smaller values than those required with
ceramic capacitors provide more phase margin a
with greater loop crossover frequency.
Layout
Figures 1 and 2 display the suggested PCB layout
for the AAT1154. The following guidelines should
be used to help insure a proper layout.
1. The connection from the input capacitor to the
Schottky anode should be as short as possible.
2. The input capacitor should connect as closely as
possible to V
POWER
(pins 5 and 8) and GND (pin 2).
3. C1, L1, and CR1 should be connected as
closely as possible. The connection from the cath-
ode of the Schottky to the LX node should be as
short as possible.
4. The feedback trace (pin 1) should be separate
from any power trace and connect as closely as
possible to the load point. Sensing along a high
current load trace can degrade DC load regulation.
5. The resistance of the trace from the load
return to the gnd (pin 2) should be kept to a mini-
mum. This will help to minimize any error in DC
regulation due to differences in the potential of the
internal reference ground and the load rtn.
6. R1 and C3 are required in order to provide
a cleaner power source for the AAT1154 control
circuitry.
RIPPLE
V
ESR
I
(
)
(
)
1
2
3
OUT
FWD
IN
OUT
RMS
IN
V
V
V
V
I
L F V
+
-
=
1
O
O
O
RMS
IN
IN
V
V
I
I
V
V
=
-
Diodes Inc.
B340LA
0.45V@3A
ROHM
RB050L-40
0.45@3A
Micro Semi
5820SM
0.46V@3A
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
11
AAT1154
1MHz 3A Buck DC/DC Converter
12
1154.2004.08.1.2
Thermal
The losses associated with the AAT1154 output
switching MOSFET are due to switching losses
and conduction losses. The conduction losses are
associated with the R
DS(ON)
characteristics of the
output switching device. At the full load condition,
assuming continuous conduction mode (CCM), an
accurate calculation of the R
DS(ON)
losses can be
derived from the following equations.
R
DS(ON)
losses
Internal switch RMS current
D is the duty cycle and V
F
is the forward drop of the
Schottky diode.
I
Q
is the peak to peak inductor ripple current.
A simplified form of calculating the R
DS(ON)
and
switching losses is given by
where I
Q
is the AAT1154 quiescent current.
Once the total losses have been determined the
junction temperature can be derived. The thermal
resistance (
JA
) for the SO-8 package mounted on
an FR4 printed circuit board in still air is 110C/W.
T
J
= P
JA
+ T
AMB
T
AMB
is the maximum ambient temperature and T
J
is the resultant maximum junction temperature.
Design Example
I
OUT
3A
I
RIPPLE
30% of full load at max Vin
V
OUT
3.3V
V
IN
5V
5%
F
S
1MHz
T
MAX
= 70C
Inductor Selection
Use standard value of 1.5 H
1
3.3
3.3
1
1.25
H
3
0.3 1
5
OUT
OUT
O
IN
V
V
L
I
k F
V
V
V
A
MHz
V
=
-
=
-
=
2
O
DS(ON)
o
SW
O
Q
IN
IN
I
R
V
P
t
F I
I
V
V
=
+
+
O
F
IN F
V
V
D
V
V
+
=
+
2
2
12
RMS
O
I
I
I
D
=
+
2
ON
RMS
DS(ON)
P
I
R
=
Figure 1. AAT1154 Fixed Output Top Side
Figure 2. AAT1154 Fixed Output Bottom
Layout
Side Layout
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
13
Sumida inductor Series CDRH6D38.
AAT1154 Junction Temperature
Diode
Given a case to ambient thermal resistance of
120C/W from the manufacturer's data sheet,
T
J(MAX)
of the diode is
Output Capacitor
The output capacitor value required for sufficient
loop phase margin depends on the type of capaci-
tor selected. For a low ESR ceramic capacitor a
minimum value of 200F is required. For a low
ESR tantalum capacitor lower values are accept-
able. While the relatively higher ESR associated
with the tantalum capacitor will give more phase
margin and a more damped transient response, the
output voltage ripple will be higher.
The 120F Vishay 594D tantalum capacitor has an
ESR of 85 m
and a ripple current rating of 1.48
Arms in a C case size. Although smaller case sizes
are sufficiently rated for this ripple current, their
ESR level would result in excessive output ripple.
The ESR requirement for a tantalum capacitor can
be estimated by
Two or three 1812 X5R 100uF 6.3V ceramic
capacitors in parallel also provide sufficient phase
margin. The low ESR and ESL associated with
ceramic capacitors also reduces output ripple sig-
nificantly over that seen with tantalum capacitors.
Temperature rise due to ESR ripple current dissi-
pation is also reduced.
100
121
0.82A
RIPPLE
V
mV
ESR
m
I
=
=
(
)
(
)
1
2
3
1
3.65
1.7
240
1.5
1
5
2
3
OUT
FWD
IN
OUT
RMS
IN
V
V
V
V
I
L F V
V
V
mArms
H
MHz
V
+
-
=
=
=
J(MAX)
70
120
/
0.354
112
AMB
JA
T
T
P
C
C W
W
C
=
+
=
+
=
0.35
1.01
.354
DIODE
FW
DIODE
P
V
I
V
A
W
=
=
=
1
3.3
3
1
1.02
5
O
DIODE
O
IN
V
I
I
V
V
A
A
V
=
-
=
-
=
0.35
FW
V
V
=
2
750
5
5
2
0.539
ON
IN
IN
P
V
V
A
V
V
Watts
=
+
+ I
Q
=
+
+
=
70
110
/
0.54
129
J(MAX)
AMB
JA
T
T
P
C
C W
W
C
=
+
=
+
=
I
O
2
R
DS(ON)
V
O
3
2
65m
3.3V
t
SW
F I
O
20ns 1MHz 3A
1
3.3
3.3V
1
1.5
1
5.25V
O
O
IN
V
V
I
L F
V
V
H
MHz
=
-
=
-
2
3A + 0.41A = 3.41A
PK
OUT
I
I
I
=
+
=
= 0.82A
AAT1154
1MHz 3A Buck DC/DC Converter
14
1154.2004.08.1.2
Figure 3. 3.3 Volt 3 Amp Output
Figure 4. 5 Volt Input 3.3 Volt Output
V
IN
= 5.0V, V
OUT
= 3.3V
Efficiency vs. Load Current
60
65
70
75
80
85
90
95
100
0.01
0.1
1
10
Output Current (A)
Efficiency (%)
D1
B340LA
L1
1.5H
C2
120F
C1
10F
VP
VCC
EN
GND
FB
LX
LX
VP
U1
AAT1154-3. 3
R1
100
C3
0.1F
C3 0.1F 0603ZD104M AVX
L1 CDRH6D28-1.5H Sumida
D1 B340LA Diodes Inc.
R2
100k
C1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3
C2 MuRata 100F 6.3V GRM43-2 X5R 107M 100F 6.3V (two or three in parallel
Vin 3.5V-5.5V
Vout 3.3V @ 3A
rtn
C4
100F
C4 Vishay Sprague 100F 16V 595D107X0016C 100F 16V
C2 Vishay 120F 6.3V 594D127X96R6R3C2T
Options
C2 TDK 100F 6.3V C3325X5R0J107M 100F 6.3V (two or three in parallel)
+
-
Adjustable Output
For applications requiring an output other than the
fixed outputs available, the 1V version can be pro-
grammed externally. Resistors R3 and R4 of figure 5
force the output to regulate higher than 1 Volt. For
accurate results (less than 1% error for all outputs)
select R4 to be 10k
. Once R4 has been selected
R3 can be calculated. For a 1.25 Volt output with R4
set to 10k R3 is 2.5k
.
R3 = (V
O
- 1) R4 = 0.25 10k
= 2.5k
Input Capacitor
The input capacitor ripple is:
In the examples shown C1 is a ceramic capacitor
located as close to the IC as possible. C1 provides
the low impedance path for the sharp edges asso-
ciated with the input current. C4 may or may not be
required depending upon the impedance charac-
teristics looking back into the source. It serves to
dampen out any input oscillations that may arise
from a source that is highly inductive. For most
applications where the source has sufficient bulk
capacitance and is fed directly to the AA1154
through large PCB traces or planes it is not
required. When operating the AAT1154 evaluation
board on the bench C4 is required due to the
inductance of the wires running from the laborato-
ry power supply to the evaluation board.
1
1.42
O
O
RMS
O
IN
IN
V
V
I
I
Arms
V
V
=
-
=
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
15
Figure 5. AAT1154 Evaluation Board with adjustable output
Figure 6. Evaluation Board Top Side
Figure 7. Evaluation Board Bottom Side
D1
B340LA
L1
1.5H
C2
120F
C1
10F
VP
VCC
EN
GND
FB
LX
LX
VP
U1
AAT1154-1.0
R1
100
C3
0.1F
C3 0.1F 0603ZD104M AVX
L1 CDRH6D28-1.5H Sumida
D1 B340LA Diodes Inc.
R2
100k
C1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3
C2 MuRata 100uF 6.3V GRM43-2 X5R 107M 100F 6.3V (two or three in parallel)
Vin 2.7V-5.5V
V
OUT
1.25V @ 3A
rtn
C4
100F
C4 Vishay Sprague 100F 16V 595D107X0016C 100F 16V
R3
2.55k
R4
10.0k
C2 Vishay 120F 6.3V 594D127X96R6R3C2T
Options
C2 TDK 100F 6.3V C3325X5R0J107M 100F 6.3V (two or three in parallel)
AAT1154
1MHz 3A Buck DC/DC Converter
16
1154.2004.08.1.2
Capacitors
Inductors
Diodes
Manufacturer
Part Number
Vfwd
Diodes Inc.
B340LA
0.45V @ 3A
ROHM
RB050L-40
0.45 @ 3A
Micro Semi
5820SM
0.46V @ 3A
Inductance
I DCR
Height
Part Number
Manufacturer
(H)
(Amps)
(
)
(mm)
CDRH6D38-4763-T055 Sumida
1.5
4.0
.014
4.0
shielded
N05D B1R5M
Taiyo Yuden
1.5
3.2
.025
2.8
Non shielded
NP06DB B1R5M
Taiyo Yuden
1.5
3.0
.022
3.2
shielded
LQH55DN1R5M03
MuRata
1.5
3.7
.022
4.7
Non shielded
LQH66SN1R5M03
MuRata
1.5
3.8
.016
4.7
shielded
Capacitance
Voltage
Part Number
Manufacturer
(F)
(V)
Temp Co.
Case
C4532X5ROJ107M
TDK
100
6.3
X5R
1812
GRM43-2 X5R 107M 6.3
MuRata
100
6.3
X5R
1812
GRM43-2 X5R 476K 6.3
MuRata
47
6.3
X5R
1812
GRM42-6 X5R 106K 6.3
MuRata
10
6.3
X5R
1206
594D127X_6R3C2T
Vishay
120
6.3
C case
595D107X0016C
Vishay
100
16
C case
AAT1154
1MHz 3A Buck DC/DC Converter
1154.2004.08.1.2
17
Ordering Information
Package Information
SO-8
All dimensions in millimeters.
0.175
0.075
6.00
0.20
3.90
0.10
1.55
0.20
1.27 BSC
0.42
0.09
8
4.90
0.10
4
4
45
0.375
0.125
0.235
0.045
0.825
0.445
Output Voltage
Package
Marking
Part Number (Tape and Reel)
1.0V (Adj. V
OUT
1.0V)
SO-8
AAT1154IAS-1.0-T1
1.8V
SO-8
AAT1154IAS-1.8-T1
2.5V
SO-8
AAT1154IAS-2.5-T1
3.3V
SO-8
AAT1154IAS-3.3-T1
AAT1154
1MHz 3A Buck DC/DC Converter
18
1154.2004.08.1.2
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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