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PDF LA8517JG Data sheet ( Hoja de datos )
| Número de pieza | LA8517JG | |
| Descripción | 3A/23V Step-Down DC-DC Converter | |
| Fabricantes | Linear Artwork | |
| Logotipo |  |
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General Description
LA8517
300KHz, 3A/23V Step-Down DC-DC Converter
Features
LA8517 is a voltage mode, step-down DC-DC
converter that is designed to meet 3A output
current, and utilizes PWM control scheme that
switches with 300KHz fixed frequency.
The input voltage range of LA8517 is from 3.6V
to 23V, and available in adjustable output
voltage from 0.8V to VIN. The supply current is
only 3mA during operation and under 1uA in
shutdown.
This device provides an enable function that
can be controlled by external logic signal. It
also provides excellent regulation during line
or load transient. Other features of current
limit, thermal shutdown protection, and short
circuit protection are also included. Due to the
low RDS(ON) of the internal power MOSFET, this
device provides high efficiency step-down
applications. It can also operate with a
maximum duty cycle of 100% for use in low
drop-out conditions. The package is available
in standard SOP-8.
l Adjustable Output Voltage from 0.8V to VIN
l 3.6V to 23V Input Voltage Range
l Continuous 3A Output Capability
l 300KHz Oscillation Frequency
l 0.8V Reference Voltage
l 1uA Low Shutdown Current
l 3mA Low Supply Current
l 100% Duty Cycle
l Built-in Low RDS(ON) Power MOSFET
l No External Compensation Required
l Support Low ESR Output Ceramic Capacitors
l Adjustable Current Limit
l Short Circuit and Thermal Protection
l SOP-8 Package
l Meet RoHS Standard
Applications
l Broadband Communication Device
l LCD TV / Monitor
l Storage Device
l Wireless Application
Ordering Information
Marking Information
LA8517 1 2 3 4
1 (Package Type) => J: SOP
2 (Number of Pins) => G: 8pin
3 (Output Voltage) => Blank: Adjustable
4 (Special Feature) => Blank: N/A
Available Part Number
LA8517JG
LA8517JG
1234
1 2 (Date Code)
For date code rule, please contact our sales
representative directly
3 4 (Internal Code)
LA8517-A01
-1-
Aug. 27, 2009
1 page  
Functional Block Diagram
SW
IN
Thermal
Shutdown
LA8517
300KHz
OSC
0.8V Reference Voltage
PWM-Switched
Control Circuit
+
-
FB
VON/OFF
90uA
GND
Pin Configurations
EN
OCSET
FB
EN
OCSET
IN
SOP-8
GND
GND
SW
SW
Pin No.
1
2
3
4
5,6
7,8
Name
FB
EN
OCSET
IN
SW
GND
Description
This pin senses the feedback voltage to regulate the output voltage.
Connect this pin to a voltage divider to set the output voltage.
This pin allows an external control signal to turn-on/off this device. Float this
pin or force it below 0.8V to turn-off this device, force it above 2V to turn-on
this device. If this feature is not needed, connect this pin to IN directly.
Add an external resistor from this pin to IN to set current Limit.
The input pin of the step-down converter.
A suitably large capacitor must be connected from this pin to ground to
bypass noise on the input of the IC.
The output pin of the step-down converter.
This pin is the switching node that supplies power to the output. Connect a
LC filter from this pin to the output load and a rectifier diode to the ground.
The ground pin of the step-down converter.
Connect this pin to the circuit ground.
LA8517-A01
-5-
Aug. 27, 2009
5 Page 
LA8517
Application Information
Output Voltage Programming
LA8517 develops a band-gap between the feedback pin and ground pin. Therefore, the output
voltage can be formed by R1 and R2. Use 1% metal film resistors for the lowest temperature
coefficient and the best stability. Select lower resistor value to minimize noise pickup in the
sensitive feedback pin, or higher resistor value to improve efficiency.
The output voltage is given by the following formula:
VOUT = VFB x ( 1 + R1 / R2 ) where VFB = 0.8V
SW
FB
GND
VOUT
R1
R2
VFB
Short Circuit Protection
When the output is shorted to ground, the protection circuit will be triggered and force the
oscillation frequency down to approximately 50KHz. The oscillation frequency will return to
300KHz once the output voltage or the feedback voltage rises above 0V.
Current Limit Setting
This device reserves OCSET pin to set the switching peak current. In general, the peak current
must be 1.5 times of the continuous output current. It can be calculated as below:
VIN
ROCSET
IN
OCSET GND
ICL = (IOCSET x ROCSET) / RDS(ON)
Where ICL is the current limit, IOCSET is the OCSET bias current (90uA Typ.), and RDS(ON) is the
ON-resistance of the internal power MOSFET.
Delay Start-up
The following circuit uses the EN pin to provide a time delay between the input voltage is applied
and the output voltage comes up. As the instant of the input voltage rises, the charging of
capacitor CDELAY pulls the EN pin low, keeping the device off. Once the capacitor voltage rises above
LA8517-A01
- 11 -
Aug. 27, 2009
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LA8517JG.PDF ] | |
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