Document
LA8509
380KHz, 18V/3A Synchronous Step-Down DC-DC Converter
General Description
Features
The LA8509 is a current mode, synchronous step-down DC-DC converter that is designed to meet 3A output current, and utilizes PWM control scheme that switches with 380KHz fixed frequency.
The input voltage range of LA8509 is from 4.5V to 18V, and available in adjustable output voltage from 0.925V to 12V. The supply current is only 1.2mA 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 due to the current mode operation. Other features of current limit, soft-start, 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 is available in SOP-8 package.
l Continuous 3A Output Capability l 0.925V Reference Voltage l 4.5V to 18V Input Voltage Range l Adjustable Output from 0.925V to 12V l 380KHz Oscillation Frequency l 1uA Low Shutdown Current l 1.2mA Low Supply Current l Current Mode for Excellent Response l Support Low ESR Output Ceramic Capacitors l Internal Current Limit l Soft-Start l Short Circuit Protection l Thermal Shutdown 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
LA8509 1 2 3 4 1 (Package Type) => P: ESOP 2 (Number of Pins) => G: 8pin 3 (Output Voltage) => Blank: Adjustable 4 (Special Feature) => Blank: N/A
Available Part Number LA8509PG
LA8509PG 1234
1 2 (Date Code) For date code rule, please contact our sales representative directly
3 4 (Internal Code)
LA8509-A01
-1-
May 29, 2011 www.linear-artwork.com
Typical Application
10nF
7V~18V
10uF MLCC
0.1uF
IN 2
EN 7
1 BS
SW
LA8509 SS
15uH
3 0.1uF
8
COMP
6 15K
GND
FB 5
44.2K
NC 3.3nF
4
10K
LA8509
5V 10uF 10uF MLCC MLCC
10nF
4.5V~18V
10uF MLCC
0.1uF
IN 2
EN 7
1 BS
SW
LA8509 SS
4.7uH
3 0.1uF
8
3.3K
COMP 6 GND
FB 5
2K
NC 6.8nF
4
6.8K
1.2V
10uF 10uF MLCC MLCC
LA8509-A01
-2-
May 29, 2011 www.linear-artwork.com
LA8509
Quick Design Table
(1). Voltage Divider and Inductor Selection Table
(IOUT = 3A, △IL = 0.6A)
L1: Recommended Inductor
R1: Output Voltage Divider
R2: Output Voltage Divider
1 10nF
VIN IN 10uF 0.1uF 2
BS SW 3
EN LA8509
7
COMP
FB
CC2
6 RC1
GND
5
CC1
4
L1
R1 R2
VOUT COUT
VIN VOUT 5V 9V 12V
1.2V 1.8V
L1 : 4.7uH R1 : 2KOhm R2 : 6.8KOhm
L1 : 4.7uH R1 : 3KOhm R2 : 3.2KOhm
L1 : 4.7uH R1 : 2KOhm R2 : 6.8KOhm
L1 : 6.8uH R1 : 3KOhm R2 : 3.2KOhm
L1 : 4.7uH R1 : 2KOhm R2 : 6.8KOhm
L1 : 6.8uH R1 : 3KOhm R2 : 3.2KOhm
2.5V 3.3V
5V
9V
L1 : 6.8uH R1 : 5.1KOhm R2 : 3KOhm
L1 : 6.8uH R1 : 5.1KOhm R2 : 3KOhm
L1 : 10uH R1 : 5.1KOhm R2 : 3KOhm
L1 : 4.7uH R1 : 10KOhm R2 : 3.9KOhm
L1 : 10uH R1 : 10KOhm R2 : 3.9KOhm
L1 : 10uH R1 : 10KOhm R2 : 3.9KOhm
L1 : 10uH R1 : 44.2KOhm R2 : 10KOhm
L1 : 15uH R1 : 44.2KOhm R2 : 10KOhm
L1 : 15uH R1 : 59KOhm R2 : 6.8KOhm
(2). Output Capacitor and Compensation Component Selection Table
RC1: Compensation Resistor CC1: 1’st Compensation Capacitor CC2: 2’nd Compensation Capacitor
COUT
VOUT
1.2V
22uF ESR ≈ 5mΩ
( MLCC)
RC1 : 1.8KOhm CC1 : 6.8nF CC2 : NC
47uF ESR ≈ 5mΩ
( MLCC)
RC1 : 3.3KOhm CC1 : 6.8nF CC2 : NC
47uF ESR ≈ 15mΩ (SMD Polymer)
RC1 : 3.3KOhm CC1 : 4.7nF CC2 : NC
330uF ESR ≈ 300mΩ (Std. AL. E-Cap)
RC1 : 22KOhm CC1 : 2.2nF CC2 : 3.9nF
330uF
RC1 : 27KOhm
ESR ≈ 50mΩ CC1 : 2.2nF
( Low ESR E-Cap) CC2 : 680pF
1.8V
RC1 : 2.5KOhm CC1 : 6.8nF CC2 : NC
RC1 : 5.1KOhm CC1 : 4.7nF CC2 : NC
RC1 : 5.1KOhm CC1 : 3.3nF CC2 : NC
RC1 : 33KOhm CC1 : 2.2nF CC2 : 2.2nF
RC1 : 39KOhm CC1 : 2.2nF CC2 : 470pF
2.5V
RC1 : 3.3KOhm CC1 : 6.8nF CC2 : NC
RC1 : 7.9KOhm CC1 : 3.3nF CC2 : NC
RC1 : 6.8KOhm CC1 : 3.3nF CC2 : NC
RC1 : 51KOhm CC1 : 2.2nF CC2 : 1.8nF
RC1 : 51KOhm CC1 : 1nF CC2 : 330pF
3.3V
RC1 : 4.7KOhm CC1 : 6.8nF CC2 : NC
RC1 : 10KOhm CC1 : 3.3nF CC2 : NC
RC1 : 10KOhm CC1 : 2.2nF CC2 : NC
RC1 : 68KOhm CC1 : 2.2nF CC2 : 1.2nF
RC1 : 68KOhm CC1 : 1nF CC2 : 220pF
5V 9V
RC1 : 6.8KOhm CC1 : 6.8nF CC2 : NC
RC1 : 12KOhm CC1 : 6.8nF CC2 : NC
RC1 : 15KOhm CC1 : 3.3nF CC2 : NC
RC1 : 25KOhm CC1 : 3.3nF CC2 : NC
RC1 : 15KOhm CC1 : 2.2nF CC2 : NC
RC1 : 27KOhm CC1 : 1nF CC2 : NC
RC1 : 100KOhm CC1 : 2.2nF CC2 : 820pF
RC1 : 180KOhm CC1 : 1nF CC2 : 390pF
RC1 : 100KOhm CC1 : 470pF CC2 : 120pF
RC1 : 180KOhm CC1 : 470pF CC2 : 82pF
LA8509-A01
-3-
May 29, 2011 www.linear-artwork.com
Functional Block Diagram
LA8509
1 .1 V FB
1 .3 V
SS 0 .9 2 5 V
COMP EN
7V Zener
2.5V
1.5V
OVP
RAMP
OSC CLK
ERROR AM PLIFIER
6uA
EN OK LOCKOUT C OM PARATO R
SHUTDOW N C OM PARATO R
CURRENT SENSE
A M P LIF IE R
SQ RQ CURRENT COMPARATOR
IN 5V
BS
SW
1.2V
OVP IN<4.10V
IN
IN T E R N A L R EGU LATO R
S
GND
Pin Configurations
BS IN SW GND
EXPOSED PAD
TIE TO GROUND.