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PDF AAT2749 Data sheet ( Hoja de datos )
| Número de pieza | AAT2749 | |
| Descripción | 3.0MHz Step-Down Converter and Low-V LDO | |
| Fabricantes | Skyworks | |
| Logotipo |  |
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DATA SHEET
AAT2749
3.0MHz Step-Down Converter and Low-VIN LDO
General Description
The AAT2749 is a two channel power regulator that oper-
ates from 2.3V to 5.5V. The AAT2749 contains a 3.0MHz,
600mA step-down converter and a low input voltage
300mA LDO regulator.
The step-down converter can deliver 600mA of load cur-
rent. The 3.0MHz switching frequency minimizes the size
of external components while keeping switching losses
low. The AAT2749 step-down converter maintains high
efficiency throughout the operating range, which is criti-
cal for portable applications. Fixed frequency, low noise
operation can be forced by a logic signal on the MODE
pin.
The AAT2749 also contains a 300mA LDO regulator with
input voltage capability as low as 1.62V. The LDO regula-
tor power input can be tied directly to the output of the
step-down regulator to increase efficiency.
Total quiescent current for the step-down converter and
LDO is a low 100μA under no load condition.
The AAT2749 is available in a Pb-free, space-saving
9-pin chip scale package (CSP) (200μm bump in 400μm
pitch) and is rated over the -40°C to +85°C temperature
range.
Features
• VIN Range: 2.3V to 5.5V
• Two Outputs
▪ VOUT_BUCK = 1.8V
▪ VOUT_LDO = 1.0V, 1.2V
• Step-Down Converter
▪ Ultra-Small 0603 Inductor (Height 1mm)
▪ Up to 92% Efficiency
▪ 3.0MHz Switching Frequency
▪ MODE Selection Pin to Select Forced PWM or PWM/
LL Operation Mode
▪ Current Limit Protection
▪ Automatic Soft Start
• LDO Regulator
▪ VINL Range: 1.62V to VIN
▪ 300mA Output Current
▪ Current Limit Protection
• 100μA No Load Quiescent Current
• Over-Temperature Protection
• -40°C to +85°C Temperature Range
Applications
• Battery-Powered Applications
• Cellular and Smart Phones
• Digital Still and Video Cameras
• PDAs, Palmtops
• Portable Instruments
Typical Application
(2.3V - 5.5V)
(1.62V - 5.5V)
IN_BUCK
CIN_BUCK
4.7μF
LX
OUT_BUCK
IN_LDO OUT_LDO
CIN_LDO
1.0μF
AAT2749
CHIP_ENABLE
MODE
GND
2.2μH
1.8V: 600mA
CBUCK
4.7μF
1.2V: 300mA
CLDO
2.2μF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
1
1 page  
Typical Characteristics
No Load Quiescent Current vs. Input Voltage
(EN_BUCK = EN_LDO = VIN; LL Mode)
150
130
110
90
70
50
30
2.3
2.8
3.3 3.8
4.3
Input Voltage (V)
T = 85°C
T = 25°C
T = -40°C
4.8 5.3
DATA SHEET
AAT2749
3.0MHz Step-Down Converter and Low-VIN LDO
No Load Quiescent Current vs. Input Voltage
(EN_BUCK = EN_LDO = VIN; PWM Mode)
14
12
10
8
6
4
2
0
2.3
2.8
3.3 3.8
4.3
Input Voltage (V)
T = 85°C
T = 25°C
T = -40°C
4.8 5.3
LDO Turn-On Response Time
(VOUT = 1.2V; VIN = 5V; IOUT = 400mA)
6 3.5
43
2 2.5
02
-2 1.5
-4 1
-6 0.5
-8 0
-10 -0.5
Time (50μs/div)
LDO Turn-Off Response Time
(VOUT = 1.2V; VIN = 5V; IOUT = 400mA)
6 3.5
43
2 2.5
02
-2 1.5
-4 1
-6 0.5
-8 0
-10 -0.5
Time (10μs/div)
LDO Line Transient Response
(VOUT = 1.2V; VIN = 4V to 5V; IOUT = 400mA)
6 1.8
5 1.7
4 1.6
3 1.5
2 1.4
1 1.3
0 1.2
-1 1.1
-2 1
Time (50μs/div)
LDO Line Transient Response
(VOUT = 1.2V; VIN = 4V to 5V; IOUT = 400mA)
6 1.8
5 1.7
4 1.6
3 1.5
2 1.4
1 1.3
0 1.2
-1 1.1
-2 1
Time (50μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
5
5 Page 
DATA SHEET
AAT2749
3.0MHz Step-Down Converter and Low-VIN LDO
CIN(MIN) =
1
VPP
IO
- ESR
· 4 · FS
Always examine the ceramic capacitor DC voltage coef-
ficient 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.
The maximum input capacitor RMS current is:
IRMS = IO ·
VO · 1 - VO
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 · 1 - VO = D · (1 - D) = 0.52 = 1
VIN VIN
2
For VIN = 2 · VO
I =RMS(MAX)
IO
2
VO · 1 - VO
The term VIN
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 AAT2749. 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 (C1) can be seen
in the evaluation board layout in the Layout section of
this datasheet.
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evalu-
ation 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 dur-
ing 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 sup-
ply, most applications do not exhibit this problem.
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic should be placed in parallel with the
low ESR/ESL bypass ceramic capacitor. This dampens
the high Q network and stabilizes the system.
Step-Down Converter Output Capacitor
The output capacitor limits the output ripple and pro-
vides holdup during large load transitions. A 2.2μF to
4.7μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL charac-
teristics 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 rela-
tionship of the output voltage droop during the three
switching cycles to the output capacitance can be esti-
mated by:
COUT
=
3 · ΔILOAD
VDROOP · FS
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
I =RMS(MAX)
1
2·
·
3
VOUT · (VIN(MAX) - VOUT)
L · FS · VIN(MAX)
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 capac-
itance will reduce the crossover frequency with greater
phase margin.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AAT2749.PDF ] | |
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