Download

AIC2350
400mA Synchronous PWM/PSM Step-Down
DC/DC Converter
 FEATURES








2.5V to 5.5V Input Voltage Range
400mA Guaranteed Output Current
Up to 95% Efficiency
Low RDS(ON) Internal Switche: 280mΩ
No Schottky Diode Required
100% Duty Cycle in Low Dropout Operation
Operating Frequency: 1.5MHz
Accurate Reference 0.6V Provides Low
Output Voltages
 APPLICATIONS







LCD TV
Multi-function Peripheral
Cellular Phones
CPU I/O Supplies
Cordless Phones
PDAs and Handy-Terminals
Battery-Operated Devices (1 Li-Ion or 3
NiMH/ NiCd)
 DESCRIPTION
The AIC2350 is a low-noise, pulse-widthmodulated (PWM), DC-DC step-down converter.
The device is available in an adjustable version
and fixed output voltages of 1.0V, 1.2V, 1.8V,
and 3.3V.
The device features an internal synchronous
rectifier for high efficiency; it requires no external
Schottky diode. The AIC2350 is ideally suited for
Li-Ion battery applications. PWM/PSM mode
extends battery life by switching to a pulseskipping-modulated mode during light loads.
Shutdown mode places the device in standby,
reducing supply current to under 1µA.
Other features of the AIC2350 include high
efficiency, low dropout voltage, short circuit
protection, over temperature protection, and
over voltage protection. It is available in a small
5 pins SOT-23 package.
 APPLICATIONS CIRCUIT
Fig. 1 Fixed Step-Down DC/DC Converter
Analog Integrations Corporation
Si-Soft Research Center
DS-2350G-01 20110118
3A1, No.1, Li-Hsin Rd. I , Science Park , Hsinchu 300, Taiwan , R.O.C.
TEL: 886-3-5772500
FAX: 886-3-5772510
www.analog.com.tw
1
AIC2350
Fig. 2 Adjustable Step-Down DC/DC Converter
 ORDERING INFORMATION
AI C2350 -XX X XX XX
PIN CONFIGURATION
PAC KING T YPE
TR: TAPE & REEL
BG: BAG
TOP VIEW
SOT-23-5
VIN
VOU T
4
5
PAC KAGE TYPE
V5: SOT-23-5
1
G: Gree n Packa ge
OUT PUT VOLTAGE
DEFAUL T: Ad j.
1 0: 1.0 V
12: 1.2V
18: 1.8V
33: 3.3V
AIC2 350-3 3GV5TR
 3.3 V Outp ut Version ,
3
EN GN D LX
TOP V IEW
Fixed version
SOT-23-5
VIN
FB
4
5
1
Exam ple:
2
2
3
EN GND LX
A djustable version
in SOT-23 -5 Gre en Package
& Tape & Re el Packin g Type
AIC2 350GV5TR
 Ad justa ble Versio n,
in SOT-23 -5 Gre en Package
& Tape & Re el Packin g Type
2
AIC2350
 ORDERING INFORMATION (Continuous)


Marking (Fixed Version)
Part No.
Marking
AIC2350-10GV5
HO10G
AIC2350-12GV5
HO12G
AIC2350-18GV5
HO18G
AIC2350-33GV5
HO33G
Marking (Adjustable Version)
Part No.
Marking
AIC2350GV5
2350G
3
AIC2350
 ABSOLUTE MAXIMUM RATINS
VIN, LX Voltage
6V
EN, FB Pin Voltage
-0.3 V to VIN
Operating Ambient Temperature Range TA
-40C to 85C
Operating Maximum Junction Temperature TJ
Storage Temperature Range TSTG
150C
-65C to 150C
260C
Lead Temperature (Soldering 10 Sec.)
Thermal Resistance Junction to Case
SOT-23-5
115C/W
Thermal Resistance Junction to Ambient
SOT-23-5
250C/W
(Assume no Ambient Airflow, no Heatsink)
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
4
AIC2350

ELECTRICAL CHARACTERISTICS
(TA=25C, VIN=3.6V unless otherwise specified.) (Note 1)
PARAMETER
CONDITIONS
SYMBOL
MIN
VIN
Output Adjustment Range
Reference Voltage
Input Voltage Range
TYP
MAX
UNITS
2.5
5.5
V
VOUT
0.6V
VIN-0.3V
V
VREF
0.588
0.612
V
IFB
-50
50
nA
0.6
FB Input Current
VFB = VIN
P-Channel On-Resistance
IOUT = 0.2A
PRDS(ON)
280
390
m
N-Channel On-Resistance
IOUT = 0.2A
NRDS(ON)
250
390
m
LX Leakage Current
VLX=0V or VLX=3.6V
1
uA
Peak Inductor Current
VIN = 5V
IPK
Quiescent Current
IOUT = 0mA,
VFB=VREF + 5%
IQ
65
85
A
Shutdown Supply Current
EN = GND
ISHDN
0.1
1
A
EN High-Level Input Voltage
VIN=2.5V to 5.5V
VEN_H
EN Low-Level Input Voltage
VIN=2.5V to 5.5V
VEN_L
-1
0.5
0.6
A
1.5
Oscillator Frequency
fOSC
1.2
Maximum Duty Cycle
DMAX
100
V
1.5
0.4
V
1.8
MHz
%
Thermal Shutdown Temperature
150
°C
Thermal Shutdown Hysteresis
25
°C
Note 1: Specifications are production tested at TA=25C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC).
5
AIC2350
 TYPICAL PERFORMANCE CHARACTERISTICS
Fig. 3 Efficiency vs. Input Voltage
Fig. 4 Efficiency vs. Output Current
Fig. 5 Efficiency vs. Output Current
Fig. 6 Efficiency vs. Output Current
Fig. 7 Output Voltage vs. Temperature
Fig. 8 Oscillator Frequency vs. Temperature
6
AIC2350

TYPICAL PERFORMANCE CHARACTERISTICS (Continuous)
Fig. 9 Oscillator Frequency vs. Input Voltage
Fig. 10 RDS(ON) vs. Input Voltage
Fig. 11 Supply Current vs. Input Voltage
Fig. 12 Current Limit vs. Input Voltage
Fig. 13 Load Transient Response
Fig. 14 Load Transient Response
7
AIC2350

TYPICAL PERFORMANCE CHARACTERISTICS (Continuous)
Fig. 15 Load Transient Response
Fig. 16 Load Transient Response
Fig. 17 PSM Operation
8
AIC2350

BLOCK DIAGRAM
Functional Block Diagram of AIC2350

PIN DESCRIPTIONS
Pin Name
Pin Function
NC
No Internal Connect (Floating or Connecting to GND).
EN
Chip Enable (Active High).
VIN
Power Input.
LX
Pin for Switching.
GND
Ground.
FB/VOUT Feedback/Output Voltage Pin.
9
AIC2350

APPLICATION INFORMATION
Operation
Short Circuit Protection
The AIC2350 is a low-noise step-down DC/DC
While the output is shorted to ground, the switching
converter
control
frequency of AIC2350 will be reduced to one third of
architecture. It features an internal synchronous
the normal switching frequency. This lower switching
rectifier, which eliminates the external Schottky diode
frequency ensures the inductor current has more time
and increases efficiency. During normal operation, the
to discharge, thereby preventing inductor current
AIC2350 can regulate its output voltage through a
runaway. The switching frequency will automatically
feedback control circuit, which is composed of an error
return to its designed value while short circuit condition
amplifier; a current comparator and several control
is released.
with
current-mode
PWM/PSM
signal generators. By comparing the feedback voltage
to the reference voltage of 0.6V, the error amplifier
varies its output voltage. The output voltage of the
error amplifier is compared with the summing signal of
current sensing signal and slope compensation signal
to determine the duty cycle of internal main power
Shutdown
By connecting the EN pin to GND, the AIC2350 can be
shut down to reduce the supply current to 0.1A
(typical). At this operation mode, the output voltage of
step-down converter is equal to 0V.
switch (P-channel MOSFET). While the main power
100% Duty Cycle Operation
switch is turned on, the synchronous power switch (N-
When the input voltage approaches the output voltage,
channel MOSFET) will be turned off through anti-short-
the AIC2350 smoothly transits to 100% duty cycle
through block. Similarly, when the main power switch
operation. This allows AIC2350 to regulate the output
is turned off, the synchronous power switch will be
voltage until AIC2350 completely enters 100% duty
turned on until the inductor current starts to reverse or
cycle operation. In 100% duty cycle mode, the output
the beginning of the next switching cycle. In order to
voltage is equal to the input voltage minus the voltage,
achieve better efficiency and prevent overcharging the
which is the drop across the main power switch.
output capacitor, AIC2350 will enter pulse-skipping-
The AIC2350 achieves 100% duty cycle operation by
modulated mode (PSM) operation while working at
extending the turn-on time of the main power switch. If
light load conditions.
the summing signal of current sensing signal and slope
Current Limitation
The AIC2350 provides current limit function by using
an internal sensing resistor. When the main power
switch turns on, current follows through the internal
sensing resistor. And current amplifier senses the
voltage, which crosses the resistor, and amplifies it.
While the sensed voltage gets higher than reference
voltage, the current limitation function is activated.
While the current limitation function is activated, the
duty cycle will be reduced to limit the output power to
protect the internal power switches.
compensation signal does not reach the output voltage
level of the error amplifier at the end of 90% switching
period, the main power switch is continuously turned
on and the oscillator remains off until the summing
signal
of
current
sensing
signal
and
slope
compensation signal reaches the output voltage level
of the error amplifier. After the summing signal of
current sensing signal and slope compensation signal
reaches the output voltage level of the error amplifier,
the main power switch is turned off and the
synchronous power switch is turned on for a constant
off time. At the end of the constant off time, the next
10
AIC2350
switching cycle is begun. While the input voltage
The selection of output capacitor depends on the
approaches
required output voltage ripple. The output voltage
the
output
voltage,
the
switching
frequency decreases gradually to smoothly transit to
100% duty cycle operation.
If input voltage is very close to output voltage, the
ripple can be expressed as:
VOUT 
IL
 ESR  IL
8  fOSC  COUT
switching mode goes from pure PWM mode to 100%
For lower output voltage ripple, the use of low ESR
duty cycle operation. During this transient state
ceramic capacitor is recommended. The tantalum
mentioned above, large output ripple voltage may
capacitor can also be used well, but its ERS is larger
appear on output terminal.
than that of ceramic capacitor.
When
Components Selection
the
input
and
output
ceramic
capacitors, X5R and X7R types are recommended
Inductor
The inductor selection depends on the current ripple of
inductor, the input voltage and the output voltage.
VOUT
L
fOSC  IL
choosing
because they retain their capacitance over wider
ranges of voltage and temperature than other types.
Output Voltage Programming (AIC2350 Adjustable
Version Only)
By connecting a resistive divider R1 and R2, the output


V
1  OUT 
V
IN 

Accepting a large current ripple of inductor allows the
voltage of AIC2350 step-down converter can be set.
use of a smaller inductance. However, higher current
VOUT can be calculated as:
ripple of inductor can cause higher output ripple

R 
VOUT  0.6  1  1 
 R2 
voltage and large core loss. By setting an acceptable
current ripple of inductor, a suitable inductance can be
obtained from above equation.
The resistive divider should sit as close to VFB pin as
possible.
In addition, it is important to ensure the inductor
saturation current exceeds the peak value of inductor
Layout Consideration
current in application to prevent core saturation. The
In order to ensure a proper operation of AIC2350, the
peak value of inductor current can be calculated
following points should be managed comprehensively.
according to the following equation.
1. The input capacitor and VIN should be placed as
IPEAK  IOUT max  
close as possible to each other to reduce the input

VOUT 
V
1  OUT 
2  fOSC  L 
VIN 
voltage ripple and noise.
2. The output loop, which is consisted of the inductor,
Input Capacitor and Output Capacitor
To prevent the high input voltage ripple and noise
resulted from high frequency switching, the use of low
ESR ceramic capacitor for the maximum RMS current
is recommended. The approximated RMS current of
the input capacitor can be calculated according to the
following equation.
2
ICINRMS  IOUT
(MAX ) 
the internal main power switch, the internal synchronous power switch and the output capacitor,
should be kept as small as possible.
3. The routes with large current should be kept short
and wide.
4. Logically the large current on the converter should
flow at the same direction.
VOUT VIN  VOUT 
2
VIN

IL2
12
5. The VFB pin should be connected to the feedback
resistors directly and the route should be away
from the noise sources.
11
AIC2350
PHYSICAL DIMENSIONS
 SOT-23-5
A
A
E
E1
D
e
e1
SEE VIEW B
WITH PLATING
c
A
A2
b
SECTION A-A
A1
BASE METAL
0.25
S
Y
M
B
O
L
GAUGE PLANE
SEATING PLANE
L
L1
θ

VIEW B
Note : 1. Refer to JEDEC MO-178AA.
2. Dimension "D" does not include mold flash, protrusions
or gate burrs. Mold flash, protrusion or gate burrs shall not
exceed 10 mil per side.
3. Dimension "E1" does not include inter-lead flash or protrusions.
4. Controlling dimension is millimeter, converted inch
dimensions are not necessarily exact.
SOT-23-5
MILLIMETERS
MIN.
MAX.
A
0.95
1.45
A1
0.00
0.15
A2
0.90
1.30
b
0.30
0.50
c
0.08
0.22
D
2.80
3.00
E
2.60
3.00
E1
1.50
1.70
e
0.95 BSC
e1
1.90 BSC
L
0.30
L1
θ
0.60
0.60 REF
0°
8°
Note:
Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other
than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its
use. We reserve the right to change the circuitry and specifications without notice.
Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to
perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a
significant injury to the user.
12
Similar pages