Analogic AAT1143IJS-3.3-T1 1mhz 400ma step-down converter Datasheet

AAT1143
1MHz 400mA Step-Down Converter
General Description
Features
The AAT1143 SwitchReg™ is a member of
AnalogicTech's Total Power Management IC™
(TPMIC™) product family. It is a 1MHz 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 AAT1143 the ideal choice for portable
applications.
•
•
The AAT1143 is available in either a fixed version
with internal feedback or a programmable version
with external feedback resistors. It can deliver
400mA of load current while maintaining a low
25µA no load quiescent current. The 1MHz switching frequency minimizes the size of external components while keeping switching losses low. The
AAT1143 feedback and control delivers excellent
load regulation and transient response with a small
output inductor and capacitor.
The AAT1143 is designed to maintain high efficiency throughout the operating range, which is critical
for portable applications.
The AAT1143 is available in a space-saving
2.0x2.1mm SC70JW-8 package and is rated over
the -40°C to +85°C temperature range.
SwitchReg™
VIN Range: 2.7V to 5.5V
VOUT Adjustable Down to 0.6V
— Fixed or Adjustable Version
25µA No Load Quiescent Current
Up to 95% Efficiency
400mA Max Output Current
1MHz Switching Frequency
Soft Start
Over-Temperature Protection
Current Limit Protection
100% Duty Cycle Low-Dropout Operation
0.1µA Shutdown Current
SC70JW-8 Package
Temperature Range: -40°C to +85°C
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•
•
•
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•
•
•
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Applications
•
•
•
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Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
Typical Application (Fixed Output Voltage)
1
5
8
VIN
LX
EN
OUT
AGND
PGND
PGND
PGND
4
2
7
6
(VOUT = 2.5V; L = 4.7µ
µH)
100
L1
VIN = 3.3V
4.7µH
C1
4.7µF
Efficiency (%)
U1
AAT1143
3
C2
4.7µF
AAT1143 Efficiency
VO
VIN
90
80
70
60
0.1
1
10
100
1000
Output Current (mA)
1143.2005.09.1.7
1
AAT1143
1MHz 400mA Step-Down Converter
Pin Descriptions
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.
Pin Configuration
SC70JW-8
(Top View)
EN
OUT
VIN
LX
2
1
8
2
7
3
6
4
5
PGND
PGND
PGND
AGND
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VOUT
VEN
TJ
TLEAD
Description
Input Voltage GND
LX to GND
OUT to GND
EN to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
6.0
-0.3 to VP + 0.3
-0.3 to VP + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
625
160
mW
°C/W
Thermal Information
Symbol
PD
θJA
Description
Maximum Power Dissipation (SC70JW-8)
Thermal Resistance2 (SC70JW-8)
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.
1143.2005.09.1.7
3
AAT1143
1MHz 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
Conditions
Step-Down Converter
VIN
Input Voltage
VUVLO
UVLO Threshold
VOUT
Output Voltage Tolerance
VOUT
Output Voltage Range
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLEAK
∆VLinereg
Quiescent Current
Shutdown Current
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
Line Regulation
VOUT
Out Threshold Voltage Accuracy
IOUT
ROUT
FOSC
TSD
THYS
Out Leakage Current
Out Impedance
Oscillator Frequency
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
VEN(L)
VEN(H)
IEN
Enable Threshold Low
Enable Threshold High
Input Low Current
Min
Typ
Max
Units
5.5
2.6
V
V
mV
V
-3.0
+3.0
%
0.6
0.6
4.0
2.5
V
50
µA
1.0
µA
mA
Ω
Ω
1
µA
0.2
%/V
615
mV
0.2
µA
kΩ
MHz
°C
°C
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0 to 400mA,
VIN = 2.7V to 5.5V
Fixed Output Version
Adjustable Output Version2
No Load, 0.6V Adjustable
Version
EN = AGND = PGND
100
1.8
25
600
0.45
0.40
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
>0.6V Output
TA = 25°C
250
0.7
VIN = VFB = 5.5V
1.4
-1.0
597
600
1.0
140
15
1.5
EN
0.6
1.0
V
V
µA
1. The AAT1143 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. For adjustable version with higher than 2.5V output, please consult your AnalogicTech representative.
4
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Efficiency vs. Load
Load Regulation
(VOUT = 2.5V; L = 4.7µ
µH)
(VOUT = 2.5V; L = 4.7µ
µH)
100
2.0
Efficiency (%)
VIN = 3.0V
Output Error (%)
VIN = 3.3V
90
VIN = 3.6V
80
70
1.0
VIN = 3.0V
0.0
VIN = 3.3V
-1.0
VIN = 3.6V
60
0.1
-2.0
1
10
100
1000
0.1
1
Output Current (mA)
1000
DC Regulation
(VOUT = 1.8V; L = 4.7µ
µH)
(VOUT = 1.8V; L = 4.7µ
µH)
100
2.0
Output Error (%)
VIN = 3.6V
VIN = 2.7V
90
Efficiency (%)
100
Output Current (mA)
Efficiency vs. Load
80
VIN = 4.2V
70
60
50
1.0
VIN = 4.2V
0.0
VIN = 2.7V
-1.0
VIN = 3.6V
-2.0
0.1
1
10
100
1000
0.1
1
Output Current (mA)
10
100
1000
Output Current (mA)
Frequency vs. Input Voltage
Output Voltage Error vs. Temperature
(VOUT = 1.8V)
(VIN = 3.6V; VO = 1.5V)
2.0
1.0
0.5
Output Error (%)
Frequency Variation (%)
10
1.0
INTERNAL DOCUMENT
DO NOT COPY
0.0
-0.5
-1.0
-1.5
-2.0
0.0
-1.0
-2.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
1143.2005.09.1.7
4.7
5.1
5.5
-40
-20
0
20
40
60
80
100
Temperature (°°C)
5
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
Switching Frequency vs. Temperature
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
35
Supply Current (µ
µA)
Variation (%)
0.20
0.10
0.00
-0.10
85°C
30
25°C
25
20
-40°C
-0.20
-40
15
-20
0
20
40
60
80
2.5
100
3.0
3.5
Temperature (°°C)
4.0
4.5
5.0
5.5
Input Voltage (V)
Load Transient Response
P-Channel RDS(ON) vs. Input Voltage
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10µ
µF)
750
1.4
1.9
100°C
Output Voltage
(top) (V)
RDS(ON) (mΩ
Ω)
120°C
1.2
600
550
85°C
500
1.0
1.8
1.7
300mA
1.6
0.8
0.6
30mA
1.5
0.4
1.4
0.2
350
1.3
0.0
300
1.2
-0.2
450
25°C
400
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Load and Inductor Current
(200mA/div) (bottom)
2.0
700
650
6.0
Time (25µs/div)
Input Voltage (V)
N-Channel RDS(ON) vs. Input Voltage
750
RDS(ON) (mΩ
Ω)
650
120°C
100°C
600
550
500
85°C
450
400
25°C
350
300
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
6
5.0
5.5
6.0
1.4
0.1
0.0
-0.1
-0.2
1.2
300mA
1.0
30mA
0.8
-0.3
0.6
-0.4
0.4
-0.5
0.2
-0.6
0.0
-0.7
-0.2
Load and Inductor Current
(200mA/div) (bottom)
700
Output Voltage (AC Coupled)
(top) (V)
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V;
C1 = 10µ
µF; C4 = 100pF; see Figure 1)
Time (25µs/div)
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
Typical Characteristics
1.9
1.2
1.8
1.0
300mA
1.7
1.6
0.8
0.6
30mA
1.5
0.4
1.4
0.2
1.3
0.0
-0.2
1.2
1.90
7.0
1.85
6.5
1.80
6.0
1.75
5.5
1.70
5.0
1.65
4.5
1.60
4.0
1.55
3.5
1.50
Input Voltage
(bottom) (V)
1.4
Load and Inductor Current
(200mA/div) (bottom)
2.0
Output Voltage
(top) (V)
Line Transient
(VOUT = 1.8V @ 400mA)
Output Voltage
(top) (V)
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7µ
µF)
3.0
Time (25µ
µs/div)
Time (25µs/div)
Line Regulation
Soft Start
(VOUT = 1.8V)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
IOUT = 100mA
-0.1
IOUT = 10mA
-0.15
-0.2
IOUT = 400mA
-0.25
-0.3
-0.35
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
4.0
3.5
3.0
3.0
2.0
2.5
1.0
2.0
0.0
1.5
-1.0
1.0
-2.0
0.5
-3.0
0.0
-4.0
-0.5
Inductor Current
(bottom) (A)
Accuracy (%)
0
-0.05
Enable and Output Voltage
(top) (V)
0.1
0.05
250µ
µs/div
Input Voltage (V)
Output Ripple
40
0.9
20
0.8
0
0.7
-20
0.6
-40
0.5
-60
0.4
-80
0.3
-100
0.2
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
0.1
-120
Time (250ns/div)
1143.2005.09.1.7
7
AAT1143
1MHz 400mA Step-Down Converter
Functional Block Diagram
VIN
OUT
See note
Err
Amp
.
DH
Voltage
Reference
LX
Logic
DL
EN
INPUT
PGND
AGND
Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly
to the internal error amplifier.
Functional Description
The AAT1143 is a high performance 400mA 1MHz
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 recommended (see table of
values).
The fixed output version requires only three external
power components (CIN, COUT, and L). The
adjustable version can be programmed with external
feedback to any voltage, ranging from 0.6V to the
8
input voltage. An additional 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 RDSON drop of the P-channel highside 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 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.
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
1
2
3
Enable
VIN
C4
100pF
U1
AAT1143
1
VOUT =1.8V
R1
2
118k
3
L1
C1
10µF
4
EN
PGND
OUT PGND
VIN
PGND
LX
AGND
8
7
6
5
4.7µH
R2
59k
C2
4.7µF
GND
LX
GND2
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7µF 10V 0805 X5R
C1 10µF 6.3V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT1143 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 protection. 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 compensation 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 AAT1143
1143.2005.09.1.7
into a low-power, non-switching state. The total
input current during shutdown is less than 1µA.
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 140°C with
15°C 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 VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all internal circuitry prior to activation.
9
AAT1143
1MHz 400mA Step-Down Converter
Applications Information
Inductor Selection
The step-down converter uses peak current mode
control with slope compensation to maintain stability
for duty cycles greater than 50%. The output inductor value must be selected so the inductor current
down slope meets the internal slope compensation
requirements. The internal slope compensation for
the adjustable and low-voltage fixed versions of the
AAT1143 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 ⋅ VO 0.75 ⋅ 1.5V
A
m=
=
= 0.24
L
4.7µH
µsec
This is the internal slope compensation for the
adjustable (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 ⋅ VO
L=
=
m
=3
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 CDRH3D16 series inductor selected
from Sumida has a 105mΩ DCR and a 900mA DC
current rating. At full load, the inductor DC loss is
17mW which gives a 2.8% loss in efficiency for a
400mA, 1.5V output.
Input Capacitor
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.
CIN =
µsec
0.75 ⋅ VO
≈ 3 A ⋅ VO
A
0.24A µsec
For high-voltage fixed versions (2.5V and above),
m = 0.48A/µsec. Table 1 displays inductor values
for the AAT1143 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
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 × VO
VIN ⎝
VIN ⎠
4
µsec
⋅ 2.5V = 7.5µH
A
In this case, a standard 10µH value is selected.
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
CIN(MIN) =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO
⎠
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the proper value. For example, the capacitance of a 10µF,
6.3V, X5R ceramic capacitor with 5.0V DC applied
is actually about 6µF.
Configuration
Output Voltage
Inductor
Slope Compensation
0.6V Adjustable With
External Resistive Divider
0.6V to 2.0V
4.7µH
0.24A/µsec
2.5V
10µH
0.24A/µsec
0.6V to 2.0V
4.7µH
0.24A/µsec
2.5V to 3.3V
4.7µH
0.48A/µsec
Fixed Output
Table 1: Inductor Values.
10
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
The maximum input capacitor RMS current is:
IRMS = IO ·
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.
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
The input capacitor RMS ripple current varies with
the input and output voltage and will always be less
than or equal to half of the total DC load current.
VO ⎛
V ⎞
· 1- O =
VIN ⎝
VIN ⎠
D · (1 - D) =
0.52 =
1
2
Output Capacitor
for VIN = 2 x VO
IRMS(MAX) =
VO
⎛
IO
2
VO ⎞
The term VIN · ⎝1 - VIN ⎠ appears in both the input
voltage ripple 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 input capacitor provides a low impedance loop
for the edges of pulsed current drawn by the
AAT1143. 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 inductance of these wires, along with the low-ESR
ceramic input capacitor, can create a high Q network that may affect converter performance. This
problem often becomes apparent in the form of
excessive ringing in the output voltage during load
transients. Errors in the loop phase and gain measurements can also result.
1143.2005.09.1.7
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.
The output capacitor limits the output ripple and
provides holdup during large load transitions. A
4.7µF to 10µF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has
the ESR and ESL characteristics necessary for low
output ripple.
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 relationship of the output voltage droop during the three switching cycles to the
output capacitance can be estimated by:
COUT =
3 · ∆ILOAD
VDROOP · FS
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
The internal voltage loop compensation also limits
the minimum output capacitor value to 4.7µF. This
is due to its effect on the loop crossover frequency
(bandwidth), phase margin, and gain margin.
Increased output capacitance will reduce the
crossover frequency with greater phase margin.
11
AAT1143
1MHz 400mA Step-Down Converter
Figure 2: AAT1143 Evaluation Board
Top Side.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1143 Evaluation Board
Bottom Side.
The maximum output capacitor RMS ripple current
is given by:
IRMS(MAX) =
1
VOUT · (VIN(MAX) - VOUT)
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.
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
12
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 59kΩ. 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 59kΩ for good noise
immunity or 221kΩ for reduced no load input current.
⎛ VOUT ⎞
⎛ 1.5V ⎞
R1 = V
-1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
The adjustable version of the AAT1143, 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 larger output capacitor C1 for stability.
Ω
R2 = 59kΩ
Ω
R2 = 221kΩ
VOUT (V)
Ω)
R1 (kΩ
Ω)
R1 (kΩ
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75
113
150
187
221
261
301
332
442
464
523
715
Thermal Calculations
There are three types of losses associated with
the AAT1143 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the
RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by
the gate charge of the power output switching
devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the LDO
losses is given by:
PTOTAL =
IO2 · (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 stepdown converter switching losses.
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
1
2
3
Enable
VIN
U1
AAT1143
1
R1
2
118k
VOUT
C1
4.7µF
3
L1
4
EN
PGND
OUT
PGND
VIN
PGND
LX
AGND
8
7
6
5
4.7µH
C2
4.7µF
R2
59k
GND
GND2
LX
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
C1, C2 4.7µF 10V 0805 X5R
Figure 5: AAT1143 Adjustable Evaluation Board Schematic.
1143.2005.09.1.7
13
AAT1143
1MHz 400mA Step-Down Converter
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dissipation reduces to:
PTOTAL = IO2 · RDSON(HS) + IQ · VIN
Since RDS(ON), quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Given the total losses, the maximum junction temperature can be derived from the θJA for the
SC70JW-8 package which is 160°C/W.
For the condition where the buck converter is in
dropout at 100% duty cycle, the total device dissipation reduces to:
PTOTAL = IO2 · RDSON(HS) + IQ · VIN
Since RDS(ON), quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Layout
The suggested PCB layout for the AAT1143 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
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 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 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 potential of the internal signal ground and the power
ground.
Given the total losses, the maximum junction temperature can be derived from the θJA for the
SC70JW-8 package which is 160°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
14
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ∆ILOAD = 300mA
VIN
= 2.7V to 4.2V (3.6V nominal)
FS
= 1.0MHz
TAMB
= 85°C
1.8V Output Inductor
L1 = 3
µsec
µsec
⋅ VO2 = 3
⋅ 1.8V = 5.4µH
A
A
(see Table 1)
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
∆IL1 =
⎛ 1.8V⎞
VO
V ⎞
1.8V
⎛
⋅ 1- O =
⋅ 1- ⎝
= 218mA
L1 ⋅ F ⎝
VIN ⎠ 4.7µH ⋅ 1.0MHz
4.2V⎠
IPKL1 = IO +
∆IL1
= 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.2V
COUT =
3 · ∆ILOAD
3 · 0.3A
=
= 4.5µF
VDROOP · FS
0.2V · 1MHz
IRMS =
(VO) · (VIN(MAX) - VO)
1
1.8V · (4.2V - 1.8V)
·
= 63mArms
=
4.7µH
· 1.0MHz · 4.2V
L1
·
F
·
V
2· 3
2· 3
IN(MAX)
1
·
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20µW
1143.2005.09.1.7
15
AAT1143
1MHz 400mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
CIN =
IRMS =
⎛ VPP
⎝ IO
1
1
=
= 4.75µF
⎞
⎛ 25mV
⎞
- 5mΩ · 4 · 1MHz
- ESR · 4 · FS
⎠
⎝ 0.4A
⎠
IO
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
AAT1143 Losses
PTOTAL =
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
VIN
+ (tsw · F · IO + IQ) · VIN
=
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
+ (5ns · 1.0MHz · 0.4A + 50µA) · 4.2V = 122mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 122mW = 104.5°C
16
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
VOUT (V)
Ω)
R1 (kΩ
Ω)
R1 (kΩ
Adjustable Version
(0.6V device)
Ω
R2 = 59kΩ
Ω1
R2 = 221kΩ
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75.0
113
150
187
221
261
301
332
442
464
523
715
VOUT (V)
Ω)
R1 (kΩ
Fixed Version
R2 Not Used
0.6-3.3V
0
L1 (µH)
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7 or 6.8
10
L1 (µH)
4.7
Table 3: Evaluation Board Component Values.
Manufacturer
Sumida
Sumida
MuRata
MuRata
MuRata
Coilcraft
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Coiltronics
Part Number
Inductance
(µH)
Max DC
Current (A)
DCR
Ω)
(Ω
Size (mm)
LxWxH
Type
CDRH3D16-4R7
CDRH3D16-100
LQH32CN4R7M23
LQH32CN4R7M33
LQH32CN4R7M53
LPO6610-472
LPO3310-472
SDRC10-4R7
SDR10-4R7
SD3118-4R7
SD18-4R7
4.7
10
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
0.90
0.55
0.45
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.21
0.20
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
3.8x3.8x1.8
3.8x3.8x1.8
2.5x3.2x2.0
2.5x3.2x2.0
2.5x3.2x1.55
5.5x6.6x1.0
3.3x3.3x1.0
4.5x3.6x1.0
5.7x4.4x1.0
3.1x3.1x1.85
5.2x5.2x1.8
Shielded
Shielded
Non-Shielded
Non-Shielded
Non-Shielded
1mm
1mm
1mm Shielded
1mm Shielded
Shielded
Shielded
Table 4: Typical Surface Mount Inductors.
1. For reduced quiescent current R2 = 221kΩ.
1143.2005.09.1.7
17
AAT1143
1MHz 400mA Step-Down Converter
Manufacturer
MuRata
MuRata
MuRata
MuRata
Part Number
Value
Voltage
Temp. Co.
Case
GRM21BR61A475KA73L
GRM18BR60J475KE19D
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7µF
4.7µF
10µF
22µF
10V
6.3V
6.3V
6.3V
X5R
X5R
X5R
X5R
0805
0603
0805
0805
Table 5: Surface Mount Capacitors.
18
1143.2005.09.1.7
AAT1143
1MHz 400mA Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
0.6
SC70JW-8
NUXYY
AAT1143IJS-0.6-T1
1.2
SC70JW-8
PBXYY
AAT1143IJS-1.2-T1
1.5
SC70JW-8
NXXYY
AAT1143IJS-1.5-T1
1.6
SC70JW-8
PYXYY
AAT1143IJS-1.6-T1
1.8
SC70JW-8
OKXYY
AAT1143IJS-1.8-T1
2.5
SC70JW-8
OYXYY
AAT1143IJS-2.5-T1
3.3
SC70JW-8
AAT1143IJS-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/pbfree.
Package Information
SC70JW-8
2.20 ± 0.20
1.75 ± 0.10
0.50 BSC 0.50 BSC 0.50 BSC
0.225 ± 0.075
2.00 ± 0.20
0.100
7° ± 3°
0.45 ± 0.10
4° ± 4°
0.05 ± 0.05
0.15 ± 0.05
1.10 MAX
0.85 ± 0.15
0.048REF
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 generally held on part numbers listed in BOLD.
1143.2005.09.1.7
19
AAT1143
1MHz 400mA Step-Down Converter
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rights, or other intellectual property rights are implied.
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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.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
20
1143.2005.09.1.7