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Número de pieza | PAM2309 | |
Descripción | 1A STEP-DOWN DC-DC CONVERTER | |
Fabricantes | Diodes | |
Logotipo | ||
Hay una vista previa y un enlace de descarga de PAM2309 (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
No Preview Available ! A Product Line of
Diodes Incorporated
PAM2309
1A STEP-DOWN DC-DC CONVERTER
Description
The PAM2309 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 PAM2309 provides a power-saving Pulse-
Skipping Modulation (PSM) mode to reduce quiescent current under
light load operation to save power.
The PAM2309 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. All versions employ internal
power switch and synchronous rectifier 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 PAM2309 is available in TSOT25, DFN2x2-6 Pin and QFN3x3-16
Pin packages.
Pin Assignments
Top View
TSOT25
Features
• Efficiency up to 96%
• Only 40µA (typ) Quiescent Current
• Output Current: Up to 1A
• Internal Synchronous Rectifier
• 1.5MHz Switching Frequency
• Soft-Start
• Under-Voltage Lockout
• Short Circuit Protection
• Thermal Shutdown
• 5-pin Small TSOT25, DFN2x2-6 Pin and QFN3x3-16 Pin
Packages
• Pb-Free Package
Applications
• Cellular Phone
• Portable Electronics
• Wireless Devices
• Cordless Phone
• Computer Peripherals
• Battery Powered Widgets
• Electronic Scales
• Digital Frame
PAM2309
Document number: DSxxxxx Rev. 2 - 1
1 of 17
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January 2013
© Diodes Incorporated
1 page A Product Line of
Diodes Incorporated
PAM2309
Typical Performance Characteristics (@TA = +25°C, CIN = 10µF, CO = 10µF, L = 4.7µH, unless otherwise specified.)
PAM2309
Document number: DSxxxxx Rev. 2 - 1
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January 2013
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5 Page A Product Line of
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PAM2309
Application Information (cont.)
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
PD = IO 2 RDS(ON)H + IQ VIN
Since RDS(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 TSOT25 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:
TSOT25 package:
PD = (125°C - 25°C)/250°C/W = 0.4W
DFN2*2 package:
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 0.5V (Typical). The output voltage is calculated as below:
VO
=
0.5x⎜⎛1 +
⎝
R1
R2
⎟⎞
⎠
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
330k
360k
470k
510k
680k
R2
240k
180k
180k
130k
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 RDS(ON) = 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 PAM2309 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.
PAM2309
Document number: DSxxxxx Rev. 2 - 1
11 of 17
www.diodes.com
January 2013
© Diodes Incorporated
11 Page |
Páginas | Total 17 Páginas | |
PDF Descargar | [ Datasheet PAM2309.PDF ] |
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