Analogic AAT1123IJS-1.2-T1 1mhz step-down converter Datasheet

AAT1123
1MHz Step-Down Converter
General Description
Features
The AAT1123 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 AAT1123 the ideal choice for portable
applications.
•
•
VIN Range: 2.7V to 5.5V
VOUT Adjustable Down to 0.6V
— Fixed or Adjustable Version
Fast Turn-On Time (100µs Typical)
25µA No Load Quiescent Current
Up to 97% Efficiency
Output Current Up to 600mA
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
•
•
•
•
•
•
•
•
•
•
•
•
The AAT1123 is available in either a fixed version
with internal feedback or a programmable version
with external feedback resistors. It can deliver up
to 600mA 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
AAT1123 feedback and control delivers excellent
load regulation and transient response with a small
output inductor and capacitor.
SwitchReg™
Applications
The AAT1123 is designed to maintain high efficiency throughout the operating range and provides
fast turn-on time.
•
•
•
•
•
•
The AAT1123 is available in a space-saving
2.0x2.1mm SC70JW-8 package and is rated over
the -40°C to +85°C temperature range.
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor / DSP Core / IO Power
PDAs and Handheld Computers
USB Devices
Typical Application (Fixed Output Voltage)
AAT1123 Efficiency
(VOUT = 2.5V; L = 10μ
μH)
VO
U1
AAT1123
3
1
C2
4.7μF
5
8
VIN
LX
EN
OUT
AGND
PGND
PGND
PGND
4
2
7
6
100
L1
4.7μH
C1
22μF
Efficiency (%)
VIN
90
VIN = 3.3V
80
70
60
0.1
1
10
100
1000
Output Current (mA)
1123.2007.02.1.6
1
AAT1123
1MHz 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
1123.2007.02.1.6
AAT1123
1MHz 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.
1123.2007.02.1.6
3
AAT1123
1MHz 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
IOUT_X
RDS(ON)H
RDS(ON)L
ILXLEAK
ΔVLinereg
Quiescent Current
Shutdown Current
Maximum Load Current
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
Line Regulation
VOUT
Out Threshold Voltage Accuracy
IOUT
ROUT
Out Leakage Current
Out Impedance
TS
Start-Up Time
FOSC
TSD
THYS
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
-3.5
+3.5
%
0.6
VIN
V
50
µA
1.0
µA
mA
Ω
Ω
1
µA
0.5
%/V
609
mV
0.2
µA
kΩ
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0 to 600mA,
VIN = 2.7V to 5.5V
100
1.8
No Load, 0.6V Adjustable
Version
EN = AGND = PGND
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
From Enable to Output
Regulation
TA = 25°C
591
600
250
100
0.7
1.0
140
15
µs
1.5
MHz
°C
°C
0.6
V
V
µA
EN
VIN = VFB = 5.5V
1.4
-1.0
1.0
1. The AAT1123 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.
4
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 3.3V; L = 10μ
μH)
(VOUT = 3.3V; L = 10μ
μH)
3.0
90
Output Error (%)
Efficiency (%)
100
VIN = 3.9V
VIN = 4.2V
80
70
2.0
VIN = 4.2V
1.0
0.0
-1.0
VIN = 3.9V
-2.0
-3.0
60
0.1
1
10
100
0.1
1000
1
10
Efficiency vs. Load
100
1000
100
1000
DC Regulation
(VOUT = 2.5V; L = 10μ
μH)
(VOUT = 2.5V; L = 10μ
μH)
3.0
100
Output Error (%)
VIN = 3.3V
Efficiency (%)
1000
Output Current (mA)
Output Current (mA)
90
VIN = 3.0V
VIN = 3.6V
80
70
VIN = 3.3V
2.0
VIN = 3.6V
1.0
0.0
VIN = 3.0V
-1.0
-2.0
-3.0
60
0.1
1
10
100
1000
0.1
1
10
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 1.5V; L = 4.7μ
μH)
(VOUT = 1.5V; L = 4.7μ
μH)
3.0
100
VIN = 2.7V
VIN = 3.6V
Output Error (%)
90
Efficiency (%)
100
80
VIN = 4.2V
70
60
50
VIN = 4.2V
2.0
VIN = 3.6V
1.0
0.0
VIN = 2.7V
-1.0
-2.0
-3.0
0.1
1
10
Output Current (mA)
1123.2007.02.1.6
100
1000
0.1
1
10
Output Current (mA)
5
AAT1123
1MHz Step-Down Converter
Typical Characteristics
Output Voltage Error vs. Temperature
Frequency vs. Input Voltage
(VIN = 3.6V; VO = 2.5V)
(VOUT = 1.8V)
2.0
1.5
0.5
Output Error (%)
Frequency Variation (%)
1.0
0.0
-0.5
-1.0
-1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-40
-2.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-20
0
20
60
80
100
Temperature (°°C)
Input Voltage (V)
Switching Frequency vs. Temperature
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
0.20
35
Supply Current (μ
μA)
Variation (%)
40
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)
5.0
5.5
6.0
N-Channel RDS(ON) vs. Input Voltage
750
750
700
700
650
120°C
650
100°C
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
4.5
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
600
550
85°C
500
450
25°C
400
120°C
100°C
600
550
500
85°C
450
400
25°C
350
350
300
300
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
6
4.0
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
Typical Characteristics
Load Transient Response
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22μ
μF)
1.3
1.1
300mA
30mA
0.9
0.7
0.5
0.3
0.1
-0.1
2.65
1.5
2.55
Output Voltage
(top) (V)
1.5
1.3
0.9
30mA
2.35
0.7
2.25
0.5
0.3
2.15
0.1
2.05
-0.1
Time (25μs/div)
Time (25μs/div)
Line Transient
Line Regulation
(VOUT = 2.5V @ 500mA)
(VOUT = 1.5V)
7.0
2.55
6.5
2.50
6.0
2.45
5.5
2.40
5.0
2.35
4.5
2.30
2.25
4.0
2.20
3.5
2.15
3.0
2
1.5
Accuracy (%)
2.60
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
1.1
300mA
2.45
Load and Inductor Current
(200mA/div) (bottom)
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
Load and Inductor Current
(200mA/div) (bottom)
Output Voltage
(top) (V)
(30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22μ
μF)
IOUT = 600mA
1
0.5
IOUT = 100mA
0
IOUT = 10mA
-0.5
-1
2.5
Time (25μ
μs/div)
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Soft Start
Output Ripple
(VIN = 3.6V; VOUT = 1.5V; L = 4.7μ
μH)
0.8
0
0.7
0.6
-20
0.5
-40
0.4
-60
0.3
-80
0.2
-100
0.1
-120
Time (250ns/div)
1123.2007.02.1.6
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)
20
Enable and Output Voltage
(top) (V)
0.9
40
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
Time (50μs/div)
7
AAT1123
1MHz 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
can also be added to the external feedback to provide improved transient response (see Figure 1).
The AAT1123 is a high performance 600mA 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 22µF ceramic
capacitor are recommended (see Table of Values).
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input voltage minus the RDSON drop of the P-channel highside MOSFET.
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
input voltage. An additional feed-forward capacitor
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.
8
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 heavy load.
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
1
2
3
VIN
Enable
U1
AAT1123
C4 100pF
1
2
R1 118k
VOUT
C1
22μF
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 AAT1123 SC70JW-8
L1 CDRH3D16-4R7
C1 22μF 6.3V 0805 X5R
C2 4.7μF 6.3V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT1123 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 AAT1123
into a low-power, non-switching state. The total
1123.2007.02.1.6
input current during shutdown is less than 1µA.
The AAT1123 provides turn-on within 100µs (typical) of the enable input transition.
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
AAT1123
1MHz 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
AAT1123 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
µsec
0.75 ⋅ VO
≈ 3 A ⋅ VO
A
0.24A µsec
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 =
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
⎛ 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.
For high-voltage fixed versions (2.5V and above),
m = 0.48A/µsec. Table 1 displays inductor values
for the AAT1123 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
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 to 3.3V
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
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
The maximum input capacitor RMS current is:
IRMS = IO ·
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 =
for VIN = 2 x VO
IRMS(MAX) =
1
2
VO
⎛
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
AAT1123. 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.
IO
2
Figure 2: AAT1123 Evaluation Board
Top Side.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1123 Evaluation Board
Bottom Side.
1123.2007.02.1.6
11
AAT1123
1MHz Step-Down Converter
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.
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
22µF X5R or X7R ceramic capacitor 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 · ΔILOAD
VDROOP · FS
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
12
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
The internal voltage loop compensation limits the
minimum output capacitor value to 22µF. 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.
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
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 ⎠
⎝
⎠
The adjustable version of the AAT1123, 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.
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
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
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75
113
150
187
221
261
301
332
442
464
523
715
1000
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 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.
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dissipation reduces to:
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
Thermal Calculations
PTOTAL = IO2 · RDSON(HS) + IQ · VIN
There are three types of losses associated with the
AAT1123 step-down converter: switching losses,
conduction losses, and quiescent current losses.
1
2
3
Enable
VIN
U1
AAT1123
1
2
R1 118k
VOUT
C1
22μF
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 AAT1123 SC70JW-8
L1 CDRH3D16-4R7
C1 22μF 6.3V 0805 X5R
C2 4.7μF 6.3V 0805 X5R
Figure 5: AAT1123 Adjustable Evaluation Board Schematic.
1123.2007.02.1.6
13
AAT1123
1MHz Step-Down Converter
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.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Layout
The suggested PCB layout for the AAT1123 is
shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout.
14
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
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.
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
Step-Down Converter Design Example
Specifications
VO
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN
= 2.7V to 4.2V (3.6V nominal)
FS
= 1.0MHz
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.
ΔIL1 =
⎛ 1.8V⎞
VO
V ⎞
1.8V
⎛
⋅ 1- O =
⋅ 1- ⎝
= 218mA
VIN ⎠ 4.7μH ⋅ 1.0MHz
4.2V⎠
L1 ⋅ F ⎝
IPKL1 = IO +
ΔIL1
= 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.05V
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 18.0μF
0.05V · 1MHz
VDROOP · FS
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
1123.2007.02.1.6
15
AAT1123
1MHz 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
AAT1123 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
1123.2007.02.1.6
AAT1123
1MHz 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
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75.0
113
150
187
221
261
301
332
442
464
523
715
1000
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
10
L1 (µH)
4.7
Table 3: Evaluation Board Component Values.
Manufacturer
Sumida
Sumida
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/HP-100
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
0.90
0.84
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.23
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
4.0x4.0x1.8
4.0x4.0x1.8
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
1mm
1mm
1mm Shielded
1mm Shielded
Shielded
Shielded
Table 4: Typical Surface Mount Inductors.
1. For reduced quiescent current R2 = 221kΩ.
1123.2007.02.1.6
17
AAT1123
1MHz Step-Down Converter
Manufacturer
MuRata
TDK
Taiyo-Yuden
Part Number
Value
Voltage
Temp. Co.
Case
GRM21BR60J226ME39
C2012X5R0J226K
JMK212BJ226KL
22µF
22µF
22µF
6.3V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 5: Surface Mount Capacitors.
18
1123.2007.02.1.6
AAT1123
1MHz Step-Down Converter
Ordering Information
Output Voltage1
Package
Marking2
Part Number (Tape and Reel)3
0.6
1.2
1.5
1.8
2.5
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
SC70JW-8
PMXYY
VTXYY
AAT1123IJS-0.6-T1
AAT1123IJS-1.2-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.
1123.2007.02.1.6
19
AAT1123
1MHz Step-Down Converter
© Advanced Analogic Technologies, Inc.
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20
1123.2007.02.1.6