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PDF AAT1155 Data sheet ( Hoja de datos )
| Número de pieza | AAT1155 | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | AAT | |
| Logotipo |  |
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AAT1155
1MHz 2.5A Step-Down DC/DC Converter
General Description
The AAT1155 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 2.5A with an internal power MOS-
FET, the current-mode controlled IC provides high
efficiency. Fully internally compensated, the
AAT1155 simplifies system design and lowers
external parts count.
The AAT1155 is available in a Pb-free MSOP-8
package and is rated over the -40°C to +85°C tem-
perature range.
Features
SwitchReg™
• 5.5V Max Supply Input
• Fixed or Adjustable VOUT: 1.0V to 4.2V
• 2.5A Output Current
• Up to 95% Efficiency
• Integrated Low On Resistance Power
Switches
• Internally Compensated Current Mode Control
• 1MHz Switching Frequency
• Constant PWM Mode
• Low Output Ripple With Light Load
• 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
•
•www.DataSheet4U.com
•
•
•
Cable/DSL Modems
Computer Peripherals
High Efficiency Conversion from 5V or 3.3V
Supply
Network Cards
Set-Top Boxes
VP
AAT1155
ENABLE
FB
LX
LX
VCC
GND
1.5µH
120µF
OUTPUT
1155.2005.11.1.6
1
1 page  
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
Typical Characteristics
RDS(ON) vs. Temperature
90
2.7V
80
3.6V
4.2V
70
60
5.0V 5.5V
50
40
-20 0 20 40 60 80 100 120
Temperature (°C)
Oscillator Frequency Variation
vs. Input Voltage
(VOUT = 3.3V)
0.5
0.25
0
-0.25
-0.5
3.5
4 4.5
Input Voltage (V)
5
5.5
80
75
70
65
60
55
50
45
40
2.5
RDS(ON) vs. Input Voltage
(IDS = 1A)
3 3.5 4 4.5 5
Input Voltage (V)
5.5
Oscillator Frequency Variation vs. Temperature
(VIN = 5V)
1
0
-1
-2
-3
-4
-20 0 20 40 60 80 100
Temperature (°C)
Enable Threshold vs. Input Voltage
1.2
1.1
EN(H)
1
0.9
0.8
0.7 EN(L)
0.6
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Output Voltage Variation vs. Temperature
(IOUT = 2A; VO = 3.3V)
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-20 0 20 40 60 80 100
Temperature (°C)
1155.2005.11.1.6
5
5 Page 
AAT1155
1MHz 2.5A Step-Down DC/DC Converter
Schottky Freewheeling Diode
The Schottky average current is the load current
multiplied by one minus the duty cycle.
⎛⎝1-
VO ⎞
VIN ⎠
For VIN at 5V and VOUT at 3.3V, the average diode
current is:
IAVG =
IO ·
⎛1-
⎝
VO ⎞ = 2.5A · ⎛1-
VIN ⎠
⎝
3.3V ⎞
5.0V⎠
=
0.85A
With a 125°C maximum junction temperature and a
120°C/W thermal resistance, the maximum aver-
age current is:
IAVG
=
TJ(MAX)- TAMB
θJ-A · VFWD
=
125°C - 70°C
120°C/W · 0.4V
= 1.14A
For overload, short-circuit, and excessive ambient
temperature conditions, the AAT1155 enters over-
temperature shutdown mode protecting the
AAT1155 as well as the output Schottky. In this
mode, the output current is limited internally until
the junction temperature reaches the temperature
limit (see over-temperature characteristics graphs).
The diode reverse voltage must be rated to with-
stand the input voltage.
3A Surface Mount Schottky Diodes
Diodes Inc.
ROHM
Micro Semi
B340LA
RB050L-40
5820SM
0.45V @ 3A
0.45 @ 3A
0.46V @ 3A
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 AAT1155. A low ESR/ESL
ceramic capacitor is ideal for this function. To mini-
mize stray inductance, the capacitor should be
placed as closely 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 AAT1155. Proper placement of the input
capacitor C1 is shown in the layout in Figure 2.
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 1µF to
10µF. 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.
IRMS = IO ·
VO ·⎛1- VO ⎞
VIN ⎝ VIN ⎠
1155.2005.11.1.6
Vin 3.5V-5.5V
C4
100µF
R1 R2
100 100k
C1
10µF
C3
0.1µF
U1
AAT1155-3.3
FB VP
GND LX
EN LX
VCC VP
Vout 3.3V @ 2.5A
L1
1.5µH
D1 C2
B340LA 120µF
+
-
rtn C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Vishay120µF 6.3V 594D127X96R6R3C2T
C3 0.1µF 0603ZD104M AVX
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
D1 B340LA Diodes Inc.
L1 CDRH6D28-1.5µH Sumida
Options
C2 MuRata 100µF 6.3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel)
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
Figure 2: 3.3V, 3A Output Efficiency.
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AAT1155.PDF ] | |
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