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Teilenummer | AAT1150 |
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Beschreibung | 1MHz 1A Step-Down DC/DC Converter | |
Hersteller | Advanced Analogic Technologies | |
Logo | ||
Gesamt 16 Seiten AAT1150
1MHz 1A Step-Down DC/DC Converter
General Description
The AAT1150 SwitchReg™ is a member of
AnalogicTech's Total Power Management IC™
(TPMIC™) product family. The step-down switch-
ing converter is ideal for applications where high
efficiency, small size, and low ripple are critical.
Able to deliver 1A with internal power MOSFETs,
the current-mode controlled IC provides high effi-
ciency using synchronous rectification. Fully inter-
nally compensated, the AAT1150 simplifies system
design and lowers external parts count.
The AAT1150 is available in an MSOP-8 package
and is rated over the -40°C to +85°C temperature
range.
Features
SwitchReg™
• VIN Range: 2.7V to 5.5V
• Up to 95% Efficiency
• 110mΩ RDS(ON) MOSFET Switch
• <1.0µA of Shutdown Current
• 1MHz Switching Frequency
• Fixed or Adjustable VOUT: 1.0V to 4.2V
• High Initial Accuracy: ±1%
• 1.0A Peak Current
• Integrated Power Switches
• Synchronous Rectification
• Internally Compensated Current Mode Control
• Constant PWM Mode for Low Output Ripple
• Internal Soft Start
• Current Limit Protection
• Over-Temperature Protection
• MSOP-8 package
• -40°C to +85°C Temperature Range
Typical Application
INPUT
10µF
100Ω
0.1µF
Applications
• Cable/DSL Modems
• Computer Peripherals
• High Efficiency Conversion From 5V or 3.3V
Supply
• Network Cards
• Set-Top Boxes
VP
AAT1150
FB
ENABLE
LX
VCC
SGND
PGND
4.1µH
2x 22µF
OUTPUT
1150.2005.03.1.2
1
AAT1150
1MHz 1A Step-Down DC/DC Converter
Typical Characteristics
Output Voltage vs. Temperature
(IOUT = 900mA; VOUT = 1.5V)
1.0
0.6
0.2 VIN = 2.7V
-0.2
VIN = 3.6V
-0.6
-1.0
-20 0 20 40 60 80 100
Temperature (°C)
0.25
0.15
0.05
-0.05
-0.15
-0.25
2.5
Line Regulation
(VOUT = 1.5V)
IOUT = 1.0A
IOUT = 0.4A
3 3.5 4 4.5 5
Input Voltage (V)
5.5
Load Regulation
(VOUT = 1.5V; VIN = 3.6V)
0
-1
-2
-3
-4
-5
0
150 300 450 600 750 900
IOUT (mA)
Load Regulation
(VOUT = 3.3V; VIN = 5.0V)
0
-1
-2
-3
-4
-5
0
150 300
450 600
750 900 1050
Output Current (mA)
100
90
80
70
60
50
2.5
Efficiency vs. Input Voltage
(VOUT = 1.5V)
IO = 1A
IO = 0.4A
3 3.5 4 4.5 5
Input Voltage (V)
5.5
Loop Gain and Phase vs. Output Capacitor
(VIN = 3.6V; IOUT = 0.3A; CO = 22µF)
40
32
24
16
8
0
-8
-16
-24
-32
-40
10
Phase
4x
3x
2x
Gain
3x
4x
2x
100
Frequency (kHz)
225
180
135
90
45
0
-45
-90
-135
-180
-225
1000
6 1150.2005.03.1.2
6 Page AAT1150
1MHz 1A Step-Down DC/DC Converter
current varies with the input voltage and the output
voltage. The equation for the RMS current in the
input capacitor is:
IRMS = IO ⋅
VO
VIN
⋅ ⎝⎛1 -
VO ⎞
VIN ⎠
The input capacitor RMS ripple current reaches a
maximum when VIN is two times the output voltage
where it is approximately one half of the load cur-
rent. Losses associated with the input ceramic
capacitor are typically minimal and are not an
issue. Proper placement of the input capacitor can
be seen in the reference design layout shown in
Figures 4 and 5.
Output Capacitor
Since there are no external compensation compo-
nents, the output capacitor has a strong effect on
loop stability. Larger output capacitance will reduce
the crossover frequency with greater phase margin.
For the 1.5V 1.0A design using the 4.1µH inductor,
two 22µF capacitors provide a stable output. In
addition to assisting stability, the output capacitor
limits the output ripple and provides holdup during
large load transitions.
The output capacitor RMS ripple current is given by:
1
IRMS
=
2
⋅
⋅ VOUT ⋅ (VIN - VOUT)
3 L ⋅ F ⋅ VIN
For a ceramic capacitor, the dissipation due to the
RMS current of the capacitor is not a concern.
Tantalum capacitors, with sufficiently low ESR to
meet output voltage ripple requirements, also have
an RMS current rating much greater than that actu-
ally seen in this application.
Adjustable Output
For applications requiring an output other than the
fixed outputs available, the 1V version can be pro-
grammed externally (see Figure 6). Resistors R3
and R4 force the output to regulate higher than
1V. R4 should be 100 times less than the internal
1mΩ resistance of the FB pin. Once R4 is selected,
R3 can be calculated. For a 1.25V output with R4
set to 10kΩ, R3 is 2.55kΩ.
R3 = (VO - 1) ⋅ R4 = 0.25 ⋅ 10.0kΩ = 2.55kΩ
Layout Considerations
Figures 4 and 5 display the suggested PCB layout
for the AAT1150. The most critical aspect of the lay-
out is the placement of the input capacitor C1. For
proper operation, C1 must be placed as closely as
possible to the AAT1150.
Thermal Calculations
There are two types of losses associated with the
AAT1150 output switching MOSFET: switching
losses and conduction losses. Conduction losses
are associated with the RDS(ON) characteristics of
the output switching device. At full load, assuming
continuous conduction mode (CCM), a simplified
form of the total losses is:
PLOSS
= IO2 ⋅ (RDSON(H) ⋅ VO + RDSON(L) ⋅
VIN
(VIN - VO))
+ tsw ⋅ F ⋅ IO ⋅ VIN + IQ ⋅ VIN
Once the total losses have been determined, the
junction temperature can be derived from the ΘJA
for the MSOP-8 package.
12 1150.2005.03.1.2
12 Page | ||
Seiten | Gesamt 16 Seiten | |
PDF Download | [ AAT1150 Schematic.PDF ] |
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