AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
1
SwitchReg
TM
General Description
The AAT1110 SwitchRegTM is a member of
AnalogicTech's Total Power Management ICTM
(TPMICTM) product family. It is a 1.4MHz step-
down converter with an input voltage range of 2.7V
to 5.5V and output as low as 0.6V. Its low supply
current, small size, and high switching frequency
make the AAT1110 the ideal choice for portable
applications.
The AAT1110 is available in either a fixed version
with internal feedback or a programmable version
with external feedback resistors. It can deliver up
to 800mA of load current while maintaining a low
27A no load quiescent current. The 1.4MHz
switching frequency minimizes the size of external
components while keeping switching losses low.
The AAT1110 feedback and control delivers excel-
lent load regulation and transient response with a
small output inductor and capacitor.
The AAT1110 is designed to maintain high efficien-
cy throughout the operating range and provides
fast turn-on time.
The AAT1110 is available in a space-saving
2.0x2.1mm SC70JW-8 package and is rated over
the -40C to +85C temperature range.
Features
V
IN
Range: 2.7V to 5.5V
V
OUT
Fixed or Adjustable from 0.6V to V
IN
27A No Load Quiescent Current
Output Current Up to 800mA
1.4MHz Switching Frequency
120s Soft Start
Fast Load Transient
Over-Temperature Protection
Current Limit Protection
100% Duty Cycle Low-Dropout Operation
<1A of Shutdown Current
SC70JW-8 Package
Temperature Range: -40C to +85C
Applications
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
Typical Application (Fixed Output Voltage)
4.7
H
L1
22
F
C1
4.7
F
C2
EN
1
OUT
2
VIN
3
LX
4
AGND
5
PGND
6
PGND
7
PGND
8
AAT1110
U1
V
IN
V
O
Pin Descriptions
Pin Configuration
SC70JW-8
(Top View)
OUT
VIN
LX
PGND
PGND
PGND
AGND
EN
1
2
3
4
5
6
7
8
Pin #
Symbol
Function
1
EN
Enable pin.
2
OUT
Feedback input pin. This pin is connected either directly to the converter
output or to an external resistive divider for an adjustable output.
3
VIN
Input supply voltage for the converter.
4
LX
Switching node. Connect the inductor to this pin. It is internally connected to
the drain of both high- and low-side MOSFETs.
5
AGND
Non-power signal ground pin.
6, 7, 8
PGND
Main power ground return pin. Connect to the output and input capacitor
return.
AAT1110
Fast Transient 800mA Step-Down Converter
2
1110.2006.04.1.0
Absolute Maximum Ratings
1
Thermal Information
Symbol
Description
Value
Units
P
D
Maximum Power Dissipation (SC70JW-8)
625
mW
JA
Thermal Resistance
2
(SC70JW-8)
160
C/W
Symbol
Description
Value
Units
V
IN
Input Voltage to GND
6.0
V
V
LX
LX to GND
-0.3 to V
IN
+ 0.3
V
V
OUT
OUT to GND
-0.3 to V
IN
+ 0.3
V
V
EN
EN to GND
-0.3 to 6.0
V
T
J
Operating Junction Temperature Range
-40 to 150
C
T
LEAD
Maximum Soldering Temperature (at leads, 10 sec)
300
C
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
3
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-
tions 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.
Electrical Characteristics
1
T
A
= -40C to +85C, unless otherwise noted. Typical values are T
A
= 25C, V
IN
= 3.6V.
Symbol
Description
Conditions
Min
Typ
Max Units
Step-Down Converter
V
IN
Input Voltage
2.7
5.5
V
V
IN
Rising
2.7
V
V
UVLO
UVLO Threshold
Hysteresis
100
mV
V
IN
Falling
1.8
V
V
OUT
Output Voltage Tolerance
I
OUT
= 0 to 800mA,
-3.5
+3.5
%
V
IN
= 2.7V to 5.5V
V
OUT
Output Voltage Range
0.6
V
IN
V
I
Q
Quiescent Current
No Load, 0.6V Adjustable
27
70
A
Version
I
SHDN
Shutdown Current
EN = AGND = PGND
1.0
A
I
LIM
P-Channel Current Limit
800
1200
mA
R
DS(ON)H
High Side Switch On Resistance
0.45
R
DS(ON)L
Low Side Switch On Resistance
0.40
V
Linereg
Line Regulation
V
IN
= 2.7V to 5.5V
0.1
%/V
V
OUT
Out Threshold Voltage Accuracy
0.6V Output, No Load
591
600
609
mV
T
A
= 25C
I
OUT
Out Leakage Current
0.6V Output
0.2
A
R
OUT
Out Impedance
>0.6V Output
250
k
T
S
Start-Up Time
From Enable to Output
150
s
Regulation
F
OSC
Oscillator Frequency
T
A
= 25C
1.0
1.4
2.0
MHz
T
SD
Over-Temperature Shutdown Threshold
140
C
T
HYS
Over-Temperature Shutdown Hysteresis
15
C
EN
V
EN(L)
Enable Threshold Low
0.6
V
V
EN(H)
Enable Threshold High
1.4
V
I
EN
Input Low Current
V
IN
= V
OUT
= 5.5V
-1.0
1.0
A
AAT1110
Fast Transient 800mA Step-Down Converter
4
1110.2006.04.1.0
1. The AAT1110 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
5
Typical Characteristics
DC Regulation
(V
OUT
= 3.3V; L = 6.8H)
Output Current (mA)
Output Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1
1
10
100
1000
V
IN
= 4.2V
V
IN
= 5.0V
Efficiency vs. Load
(V
OUT
= 3.3V; L = 6.8H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1
1
10
100
1000
V
IN
= 4.2V
V
IN
= 5.0V
V
IN
= 3.6V
DC Regulation
(V
OUT
= 2.5V)
Output Current (mA)
Output Error (%)
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0.1
1
10
100
1000
V
IN
= 4.2V
V
IN
= 5.0V
V
IN
= 3.6V
V
IN
= 3.0V
Efficiency vs. Load
(V
OUT
= 2.5V; L = 6.8H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1
1
10
100
1000
V
IN
= 3.0V
V
IN
= 3.6V
V
IN
= 4.2V V
IN
= 5.0V
DC Regulation
(V
OUT
= 1.8V)
Output Current (mA)
Output Error (%)
-1.0
-0.5
0.0
0.5
1.0
0.1
1
10
100
1000
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
Efficiency vs. Load
(V
OUT
= 1.8V; L = 4.7H)
Output Current (mA)
Efficiency (%)
50
60
70
80
90
100
0.1
1
10
100
1000
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
Typical Characteristics
No Load Quiescent Current vs. Input Voltage
Input Voltage (V)
Supply Current (
A)
10
15
20
25
30
35
40
45
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
85
C
25
C
-40
C
Frequency vs. Input Voltage
(I
OUT
= 800mA)
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
V
OUT
= 1.8V
V
OUT
= 2.5V
V
OUT
= 3.3V
Switching Frequency vs. Temperature
(V
IN
= 3.6V; V
OUT
= 1.8V)
Temperature (
C)
Variation (%)
-15.0
-12.0
-9.0
-6.0
-3.0
0.0
3.0
6.0
9.0
12.0
15.0
-40
-20
0
20
40
60
80
100
Output Voltage Error vs. Temperature
(V
IN
= 3.6V; V
O
= 1.8V; I
OUT
= 400mA)
Temperature (
C)
Output Error (%)
-2.0
-1.0
0.0
1.0
2.0
-40
-20
0
20
40
60
80
100
Line Regulation
(V
OUT
= 1.8V)
Input Voltage (V)
Accuracy (%)
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
I
OUT
= 1mA
I
OUT
= 10mA
I
OUT
= 400mA
I
OUT
= 800mA
Soft Start
(V
IN
= 3.6V; V
OUT
= 1.8V; I
OUT
= 800mA)
Time (100
s/div)
Enable and Output Voltage
(top) (V)
Inductor Current
(bottom) (A)
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
AAT1110
Fast Transient 800mA Step-Down Converter
6
1110.2006.04.1.0
Typical Characteristics
Load Transient Response
(600mA to 800mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 10F; C
FF
= 100pF)
Output Voltage
(top) (V)
Load and Inductor Current
(100mA/div) (bottom)
Time (50s/div)
1.7
1.8
1.9
2.0
0.4
0.5
0.6
0.7
0.8
Load Transient Response
(1mA to 600mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 22F; C
FF
= 100pF)
Output Voltage
(top) (V)
Load and Inductor Current
(500mA/div) (bottom)
Time (50s/div)
1.8
2.0
2.2
-0.5
0.0
0.5
Load Transient Response
(600mA to 800mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 22F)
Output Voltage
(top) (V)
Load and Inductor Current
(100mA/div) (bottom)
Time (50s/div)
1.7
1.8
1.9
2.0
0.4
0.5
0.6
0.7
0.8
Load Transient Response
(1mA to 600mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 10F; C
FF
= 100pF)
Output Voltage
(top) (V)
Load and Inductor Current
(500mA/div) (bottom)
Time (50s/div)
1.6
1.8
2.0
2.2
-0.5
0.0
0.5
Load Transient Response
(600mA to 800mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 10F)
Output Voltage
(top) (V)
Load and Inductor Current
(100mA/div) (bottom)
Time (50s/div)
1.7
1.8
1.9
2.0
0.4
0.5
0.6
0.7
0.8
Load Transient Response
(1mA to 600mA; V
IN
= 3.6V; V
OUT
= 1.8V;
C
1
= 10F)
Output Voltage
(top) (V)
Load and Inductor Current
(500mA/div) (bottom)
Time (50s/div)
1.5
2.0
2.5
-0.5
0.0
0.5
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
7
Typical Characteristics
N-Channel R
DS(ON)
vs. Input Voltage
Input Voltage (V)
R
DS(ON)
(m
)
300
350
400
450
500
550
600
650
700
750
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
25
C
120
C
100
C
85
C
P-Channel R
DS(ON)
vs. Input Voltage
Input Voltage (V)
R
DS(ON)
(m
)
300
350
400
450
500
550
600
650
700
750
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
25
C
120
C
100
C
85
C
Output Ripple
(V
IN
= 3.6V; V
OUT
= 1.8V; I
OUT
= 1mA)
Time (10s/div)
Output Voltage (AC coupled)
(top) (mV)
Inductor Current
(bottom) (A)
-120
-100
-80
-60
-40
-20
0
20
40
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Output Ripple
(V
IN
= 3.6V; V
OUT
= 1.8V; I
OUT
= 800mA)
Time (500ns/div)
Output Voltage (AC coupled)
(top) (mV)
Inductor Current
(bottom) (A)
-60
-50
-40
-30
-20
-10
0
10
20
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
Line Response
(V
OUT
= 1.8V @ 800mA)
Output Voltage
(top) (V)
Input Voltage
(bottom) (V)
Time (50s/div)
1.66
1.68
1.70
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.86
2.6
3.1
3.6
4.1
4.6
5.1
5.6
6.1
6.6
7.1
7.6
AAT1110
Fast Transient 800mA Step-Down Converter
8
1110.2006.04.1.0
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
9
Functional Block Diagram
EN
LX
Err
.
Amp
Logic
DH
DL
PGND
VIN
OUT
AGND
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.
Functional Description
The AAT1110 is a high performance 800mA 1.4MHz
monolithic step-down converter. It has been
designed with the goal of minimizing external com-
ponent size and optimizing efficiency over the com-
plete load range. Apart from the small bypass input
capacitor, only a small L-C filter is required at the out-
put. Typically, a 4.7H inductor and a 4.7F ceramic
capacitor are recommended (see table of values).
The fixed output version requires only three external
power components (C
IN
, C
OUT
, and L). The
adjustable version can be programmed with external
feedback to any voltage, ranging from 0.6V to the
input voltage. An additional feed-forward capacitor
can also be added to the external feedback to pro-
vide improved transient response (see Figure 1).
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the R
DSON
drop of the P-channel high-
side MOSFET.
The input voltage range is 2.7V to 5.5V. The con-
verter efficiency has been optimized for all load
conditions, ranging from no load to 800mA.
The internal error amplifier and compensation pro-
vides excellent transient response, load, and line
regulation. Soft start eliminates any output voltage
overshoot when the enable or the input voltage is
applied.
AAT1110
Fast Transient 800mA Step-Down Converter
10
1110.2006.04.1.0
Control Loop
The AAT1110 is a peak current mode step-down
converter. The current through the P-channel
MOSFET (high side) is sensed for current loop
control, as well as short circuit and overload pro-
tection. A fixed slope compensation signal is added
to the sensed current to maintain stability for duty
cycles greater than 50%. The peak current mode
loop appears as a voltage-programmed current
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 compen-
sation terminates the transconductance voltage
error amplifier output. For fixed voltage versions,
the error amplifier reference voltage 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 AAT1110 into
a low-power, non-switching state. The total input
current during shutdown is less than 1A.
Current Limit and Over-Temperature
Protection
For overload conditions, the peak input current is
limited. 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 140C with
15C of hysteresis. 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 V
IN
input. Under-voltage lockout (UVLO) guarantees
sufficient V
IN
bias and proper operation of all inter-
nal circuitry prior to activation.
Figure 1: Enhanced Transient Response Schematic.
L1 CDRH3D16-4R7
4.7
H
L1
10
F
C1
4.7
F
C2
U1 AAT1110 SC70JW-8
C2 4.7
F 10V 0805 X5R
V
OUT
=1.8V
GND
V
IN
1
2
3
Enable
LX
EN
1
OUT
2
VIN
3
LX
4
AGND
5
PGND
6
PGND
7
PGND
8
AAT1110
U1
GND2
118k
R1
59k
R2
C1 10
F 6.3V 0805 X5R
100pF
C4
n/a
C3
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
11
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 induc-
tor 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
AAT1110 is 0.24A/sec. This equates to a slope
compensation that is 75% of the inductor current
down slope for a 1.5V output and 4.7H inductor.
This is the internal slope compensation for the
adjustable (0.6V) version or low-voltage fixed ver-
sions. When externally programming the 0.6V ver-
sion to 2.5V, the calculated inductance is 7.5H.
In this case, a standard 6.8H value is selected.
For high-voltage fixed versions (
2.5V), m = 0.48A/
sec. Table 1 displays inductor values for the
AAT1110 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
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 loss-
es 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 4.7H CDRH3D16 series inductor selected
from Sumida has a 105m
maximum DCR and a
900mA DC current rating. At full load, the inductor
DC loss is 67mW which gives a 4.0% loss in effi-
ciency for a 800mA, 2.5V output.
Input Capacitor
Select a 4.7F to 22F X7R or X5R ceramic capac-
itor for the input. To estimate the required input
capacitor size, determine the acceptable input rip-
ple level (V
PP
) and solve for C. The calculated
value varies with input voltage and is a maximum
when V
IN
is double the output voltage.
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the prop-
er value. For example, the capacitance of a 10F,
6.3V, X5R ceramic capacitor with 5.0V DC applied
is actually about 6F.
C
IN(MIN)
=
1
- ESR
4
F
S
V
PP
I
O
1 -
= for V
IN
= 2
V
O
V
O
V
IN
V
O
V
IN
1
4
1 -
V
O
V
IN
C
IN
=
V
O
V
IN
- ESR
F
S
V
PP
I
O
0.75
V
O
L = =
3
V
O
= 3
2.5V = 7.5H
m
0.75
V
O
0.24A
sec
A
sec
A
A
sec
0.75
V
O
m = = = 0.24
L
0.75
1.5V
4.7
H
A
sec
Table 1: Inductor Values.
Configuration
Output Voltage
Inductor
0.6V Adjustable With
1V, 1.2V
2.2H
External Feedback
1.5V, 1.8V
4.7H
2.5V, 3.3V
6.8H
Fixed Output
0.6V to 3.3V
4.7H
AAT1110
Fast Transient 800mA Step-Down Converter
12
1110.2006.04.1.0
The maximum input capacitor RMS current is:
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.
for V
IN
= 2 x V
O
The term
appears in both the input
voltage ripple and input capacitor RMS current
equations and is a maximum when V
O
is twice V
IN
.
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
AAT1110. 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 evaluation board input voltage pins. The induc-
tance of these wires, along with the low-ESR
ceramic input capacitor, can create a high Q net-
work 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 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
inductance cannot be reduced to a level that does
not affect the converter performance, a high ESR
tantalum or aluminum 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
provides holdup during large load transitions. A
4.7F to 22F X5R or X7R ceramic capacitor typi-
cally provides sufficient bulk capacitance to stabi-
lize the output during large load transitions and has
the ESR and ESL characteristics necessary for low
output ripple.
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic out-
put capacitor. During a step increase in load cur-
rent, 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 relationship of the output volt-
age droop during the three switching cycles to the
output capacitance can be estimated by:
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 4.7F. 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.
C
OUT
=
3
I
LOAD
V
DROOP
F
S
1 -
V
O
V
IN
V
O
V
IN
I
O
RMS(MAX)
I
2
=
1 -
= D
(1 - D) = 0.5
2
=
V
O
V
IN
V
O
V
IN
1
2
I
RMS
= I
O
1 -
V
O
V
IN
V
O
V
IN
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
13
The maximum output capacitor RMS ripple current
is given by:
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 volt-
age, the 0.6V version can be externally pro-
grammed. 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 suggested value for
R2 is 59k
. Although a larger value will further
reduce 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 set to either 59k
for good noise
immunity or 221k
for reduced no load input current.
R1 = -1
R2 = - 1
59k
= 88.5k
V
OUT
V
REF
1.5V
0.6V
1
2
3
V
OUT
(V
IN(MAX)
- V
OUT
)
RMS(MAX)
I
L F V
IN(MAX)
=
Figure 2: AAT1110 Evaluation Board
Figure 3: Exploded View of Evaluation
Top Side.
Board Top Side Layout.
Figure 4: AAT1110 Evaluation Board
Bottom Side.
AAT1110
Fast Transient 800mA Step-Down Converter
14
1110.2006.04.1.0
The adjustable version of the AAT1110, combined
with an external feedforward capacitor (C4 in
Figure 1), delivers enhanced transient response for
extreme pulsed load applications. The addition of
the feedforward capacitor typically requires a larg-
er output capacitor C1 for stability.
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
Thermal Calculations
There are three types of losses associated with
the AAT1110 step-down converter: switching loss-
es, conduction losses, and quiescent current loss-
es. Conduction losses are associated with the
R
DS(ON)
characteristics of the power output switch-
ing devices. Switching losses are dominated by
the gate charge of the power output switching
devices. At full load, assuming continuous conduc-
tion mode (CCM), a simplified form of the LDO
losses is given by:
I
Q
is the step-down converter quiescent current.
The term t
sw
is used to estimate the full load step-
down converter switching losses.
P
TOTAL
I
O
2
(R
DSON(HS)
V
O
+ R
DSON(LS)
[V
IN
- V
O
])
V
IN
=
+ (t
sw
F I
O
+ I
Q
) V
IN
R2 = 59k
R2 = 221k
V
OUT
(V)
R1 (k
)
R1
0.8
19.6
75K
0.9
29.4
113K
1.0
39.2
150K
1.1
49.9
187K
1.2
59.0
221K
1.3
68.1
261K
1.4
78.7
301K
1.5
88.7
332K
1.8
118
442K
1.85
124
464K
2.0
137
523K
2.5
187
715K
3.3
267
1.00M
Figure 5: AAT1110 Adjustable Evaluation Board Schematic.
L1 CDRH3D16-4R7
4.7
H
L1
10
F
C1
4.7
F
C2
U1 AAT1110 SC70JW-8
C1 10
F 10V 0805 X5R
C2 4.7
F 10V 0805 X5R
V
OUT
GND
V
IN
1
2
3
Enable
LX
EN
1
OUT
2
VIN
3
LX
4
AGND
5
PGND
6
PGND
7
PGND
8
AAT1110
U1
GND2
118k
R1
59k
R2
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
15
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dis-
sipation reduces to:
Since R
DS(ON)
, quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Given the total losses, the maximum junction tem-
perature can be derived from the
JA
for the
SC70JW-8 package which is 160C/W.
Layout
The suggested PCB layout for the AAT1110 is
shown in Figures 2, 3, and 4. The following guide-
lines 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
possible. 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 closely as possible to the load point.
Sensing along a high-current load trace will
degrade DC load regulation. If external feed-
back resistors are used, they should be placed
as closely as possible to the OUT pin (Pin 2) to
minimize the length of the high impedance
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 poten-
tial of the internal signal ground and the power
ground.
T
J(MAX)
=
P
TOTAL
JA
+ T
AMB
P
TOTAL
= I
O
2
R
DSON(HS)
+ I
Q
V
IN
AAT1110
Fast Transient 800mA Step-Down Converter
16
1110.2006.04.1.0
16
1110.2006.04.1.0
Step-Down Converter Design Example
Specifications
V
O
= 1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load
I
LOAD
= 300mA
V
IN
= 2.7V to 4.2V (3.6V nominal)
F
S
= 1.4MHz
T
AMB
= 85C
1.8V Output Inductor
(use 4.7H; see Table 1)
For Sumida inductor CDRH3D16, 4.7H, DCR = 105m
.
1.8V Output Capacitor
V
DROOP
= 0.1V
1
2
3
1
1.8V (4.2V - 1.8V)
4.7
H 1.4MHz 4.2V
2
3
RMS
I
L1 F V
IN(MAX)
=
3
I
LOAD
V
DROOP
F
S
3 0.3A
0.1V 1.4MHz
C
OUT
= =
=
6.4
F; use 10F
= 45mArms
(V
O
) (V
IN(MAX)
- V
O
)
=
P
esr
= esr I
RMS
2
= 5m
(45mA)
2
= 10
W
V
O
V
O
1.8
V
1.8V
I
L1
=
1 - = 1 - = 156mA
L1
F
V
IN
4.7
H 1.4MHz
4.2V
I
PKL1
= I
O
+
I
L1
= 0.6A + 0.068A = 0.668A
2
P
L1
= I
O
2
DCR = 0.6A
2
105m = 38mW
L1 = 3
V
O2
= 3
1.8V = 5.4H
sec
A
sec
A
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
17
Input Capacitor
Input Ripple V
PP
= 25mV
AAT1110 Losses
T
J(MAX)
= T
AMB
+
JA
P
LOSS
= 70
C + (160C/W) 268mW = 113C
P
TOTAL
+ (t
sw
F I
O
+ I
Q
) V
IN
I
O
2
(R
DSON(HS)
V
O
+ R
DSON(LS)
[V
IN
-V
O
])
V
IN
=
=
+ (5ns 1.4MHz 0.4A + 70
A) 4.2V = 268mW
0.6
2
(0.725
1.8V + 0.7 [4.2V - 1.8V])
4.2V
I
O
RMS
I
P = esr I
RMS
2
= 5m
(0.3A)
2
= 0.45mW
2
=
= 0.3Arms
C
IN
=
=
= 4.87
F; use 4.7F
1
- ESR
4
F
S
V
PP
I
O
1
- 5m
4
1.4MHz
25mV
0.6A
AAT1110
Fast Transient 800mA Step-Down Converter
18
1110.2006.04.1.0
Table 3: Evaluation Board Component Values.
Table 4: Typical Surface Mount Inductors.
Table 5: Surface Mount Capacitors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
MuRata
GRM219R61A475KE19
4.7F
10V
X5R
0805
MuRata
GRM21BR60J106KE19
10F
6.3V
X5R
0805
MuRata
GRM21BR60J226ME39
22F
6.3V
X5R
0805
Inductance
Max DC
DCR
Size (mm)
Manufacturer
Part Number
(H)
Current (A)
(
)
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
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
Adjustable Version
R2 = 59k
R2 = 221k
1
(0.6V device)
V
OUT
(V)
R1 (k
)
R1 (k
)
L1 (H)
0.8
19.6
75.0
2.2
0.9
29.4
113
2.2
1.0
39.2
150
2.2
1.1
49.9
187
2.2
1.2
59.0
221
2.2
1.3
68.1
261
2.2
1.4
78.7
301
4.7
1.5
88.7
332
4.7
1.8
118
442
4.7
1.85
124
464
4.7
2.0
137
523
6.8
2.5
187
715
6.8
3.3
267
1000
6.8
Fixed Version
R2, R4 Not Used
V
OUT
(V)
R1 (k
)
L1 (H)
0.6-3.3V
0
4.7
1. For reduced quiescent current, R2 and R4 = 221k
.
AAT1110
Fast Transient 800mA Step-Down Converter
1110.2006.04.1.0
19
Ordering Information
Package Information
SC70JW-8
All dimensions in millimeters.
0.225
0.075
0.45
0.10
0.05
0.05
2.10
0.30
2.00
0.20
7
3
4
4
1.75
0.10
0.85
0.15
0.15
0.05
1.10 MAX
0.100
2.20
0.20
0.048REF
0.50 BSC 0.50 BSC 0.50 BSC
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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
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Output Voltage
1
Package
Marking
2
Part Number (Tape and Reel)
3
Adj.
0.6
SC70JW-8
SRXYY
AAT1110IJS-0.6-T1
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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