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PDF PAM2305 Data sheet ( Hoja de datos )
| Número de pieza | PAM2305 | |
| Descripción | 1A Step-Down DC-DC Converters | |
| Fabricantes | Power Analog Micoelectronics | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de PAM2305 (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
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Features
n Efficiency up to 96%
n Only 40μA(TYP.) Quiescent Current
n Output Current: Up to 1A
n Internal Synchronous Rectifier
n 1.5MHz Switching Frequency
n Soft Start
n Under-Voltage Lockout
n Short Circuit Protection
n Thermal Shutdown
n 5-pin Small SOT23-5, DFN2x2 6-Pin and
QFN3x3 16-Pin Packages
n Pb-Free Package
Applications
n Cellular Phone
n Portable Electronics
n Wireless Devices
n Cordless Phone
n Computer Peripherals
n Battery Powered Widgets
n Electronic Scales
n Digital Frame
PAM2305
1A Step-Down DC-DC Converters
General Description
The PAM2305 is a step-down current-mode, DC-
DC converter. At heavy load, the constant-
frequency PWM control performs excellent
stability and transient response. To ensure the
longest battery life in portable applications, the
PAM2305 provides a power-saving Pulse-
Skipping Modulation (PSM) mode to reduce
quiescent current under light load operation to
save power.
The PAM2305 supports a range of input voltages
from 2.5V to 5.5V, allowing the use of a single
Li+/Li-polymer cell, multiple Alkaline/NiMH cell,
USB, and other standard power sources. The
output voltage is adjustable from 0.6V to the input
voltage, while the part number suffix PAM2305-
XX indicates pre-set output voltage of 3.3V, 2.8V,
2.5V, 1.8V, 1.5V, 1.2V or adjustable. All versions
employ internal power switch and synchronous
rectifierfor to minimize external part count and
realize high efficiency. During shutdown, the input
is disconnected from the output and the shutdown
current is less than 0.1μA. Other key features
include under-voltage lockout to prevent deep
battery discharge.
The PAM2305 is available in SOT23-5, DFN2x2 6-
Pin and QFN3x3 16-Pin packages.
wwwT.DyatpaSihceeat4lU.cAomp p l i c a t i o n
Fixed Output Voltage
VIN
CIN
10μF
1 VIN SW 5 L
GND
2
VOUT 4
3 EN /FB
Vo
Co
10μF
Adjustable Output Voltage
VIN
CIN
10μF
1 VIN
5
SW
GND
4
2 VOUT/FB
3 EN
L
R1
R2
Vo
CFW Co
10μF
VO
=
0.6 ´
æçè1 +
R1
R2
ö
÷ø
Power Analog Microelectronics,Inc
www.poweranalog.com
1
09/2008 Rev 1.2
1 page  
PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
TA=25°C, C =IN 10μF, CO=10uF, L=4.7μH, unless otherwise noted.
Efficiency vs Output Current (Vo=1.2V)
100
90
80
70
60
50
40
30
20 Vin=3.6V
10 Vin=4.2V
Vi n= 5V
0
1 10 100 1000
Output Current(mA)
Efficiency vs Output Current (Vo=1.5V)
100
90
80
70
60
50
40
30
20
1
2.5V
3.6V
4.2V
10 100 1000
Output Current(mA)
Efficiency vs Output Current (Vo=1.8V)
100
90
80
70
60
50
40
30
20
www.DataS1heet4U.com
10 100
Output Current(mA)
2.5V
3.6V
4.2V
1000
Efficiency vs Output Current (Vo=2.5V)
100
90
80
70
60
50
40
30
20
1
3V
3.6V
4.2V
10 100 1000
Output Current(mA)
100 Efficiency vs Output Current (Vo=2.8V)
90
80
70
60
50
40
30
20
1
3V
3.6V
4.2V
10 100 1000
Output Current(mA)
Eifficiency VS Output Current (Vo=3.3V)
100
90
80
70
60
50
40
30
20 Vin=3.6V
Vin=4.2V
10 Vin=5V
0
1 10 100 1000
Output Current(mA)
Power Analog Microelectronics,Inc
www.poweranalog.com
5
09/2008 Rev 1.2
5 Page 
PAM2305
1A Step-Down DC-DC Converters
For the condition where the step-down converter
is in dropout at 100% duty cycle, the total device
dissipation reduces to:
PD =IO2RDSONH +IQ VIN
Since R ,DS(ON) quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range. The maximum power dissipation
depends on the thermal resistance of IC
package, PCB layout, the rate of surrounding
airflow and temperature difference between
junction and ambient. The maximum power
dissipation can be calculated by the following
formula:
PD
=
TJ(MAX) -TA
θJA
Where TJ(max) is the maximum allowable
junction temperature 125°C.TA is the ambient
temperature and θJA is the thermal resistance
from the junction to the ambient. Based on the
standard JEDEC for a two layers thermal test
board, the thermal resistance θJA of SOT23-5
package is 250°C/W, DFN2X2 102°C/W, and
QFN3X3 68°C/W, respectively. The maximum
power dissipation at TA = 25°C can be calculated
by following formula:
SOT-25 package:
PD=(125°C-25°C)/250°C/W=0.4W
wwwD.DFaNtaS2h*e2et4pUa.ccokmage:
PD=(125°C-25°C)/102°C/W=0.984W
QFN3*3 package:
PD=(125°C-25°C)/68°C/W=1.47W
Setting the Output Voltage
The internal reference is 0.6V (Typical). The
output voltage is calculated as below:
VO=0.6×1æçè +
R1 ö
R2 ÷ø
The output voltage is given by Table 1.
Table 1: Resistor selection for output voltage
setting
Vo
1.2V
1.5V
1.8V
2.5V
3.3V
R1
100k
150k
200k
380k
540k
R2
100k
100k
100k
120k
120k
100% Duty Cycle Operation
As the input voltage approaches the output
voltage, the converter turns the P-channel
transistor continuously on. In this mode the
output voltage is equal to the input voltage minus
the voltage drop across the P - channel
transistor:
VOUT = VIN – ILOAD (Rdson + RL)
where Rdson = P-channel switch ON resistance,
ILOAD = Output current, RL = Inductor DC
resistance
UVLO and Soft-Start
The reference and the circuit remain reset until
the VIN crosses its UVLO threshold.
The PAM2305 has an internal soft-start circuit
that limits the in-rush current during start-up.
This prevents possible voltage drops of the input
voltage and eliminates the output voltage
overshoot. The soft-start acts as a digital circuit
to increase the switch current in several steps to
the P-channel current limit (1500mA).
Short Circuit Protection
The switch peak current is limited cycle-by-cycle
to a typical value of 1500mA. In the event of an
output voltage short circuit, the device operates
with a frequency of 400kHz and minimum duty
cycle, therefore the average input current is
typically 200mA.
Thermal Shutdown
When the die temperature exceeds 150°C, a
reset occurs and the reset remains until the
temperature decrease to 120°C, at which time
the circuit can be restarted.
Power Analog Microelectronics,Inc
www.poweranalog.com
11
09/2008 Rev 1.2
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet PAM2305.PDF ] | |
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