LX1684 Datasheet, PDF (1/12 Pages) Microsemi Corporation – Voltage-Mode PWM Controller

LINFINITY DIVISION
LX1684
Voltage-Mode PWM Controller
PRODUCTION
DESCRIPTION
The LX1684 is a monolithic, voltage-
mode pulse-width modulator controller.
It is designed to implement a flexible,
low cost buck (step-down) regulator
supply with a minimal of external
components.
The LX1684 has a synchronous
driver for higher efficiency and is
optimized to provide 12V to 3.3V or
12V to 2.5V regulation. It also can be
used to convert 5V or 3.3V to voltages
as low as 1.25V.
Switching frequency is fixed at
175kHz for optimal cost and space.
Short-circuit current limiting can be
implemented without expensive current
sense resistors.
Similar to the LX1682 in function but
with the positive side of the current
sense comparator brought out (CSP) to
allow it to be referenced to the topside
FET.
Current is sensed using the voltage
drop across the R_DS(ON) of the MOSFET
this sensing is delayed for 1µs to
eliminate MOSFET ringing errors.
Hiccup-mode fault protection reduces
average power to the power elements
during short-circuit conditions.
Under-voltage lockout and soft-start
are provided for optimal start-up
performance. Pulling the soft-start pin to
ground can disable the LX1684.
The small 14-pin SOIC packaging,
combined with low profile, low ESR
capacitors, and TO-252 packaged FETs
results in a high efficiency converter in a
small board area. In most cases PCB
copper can accomplish necessary heat
sinking and no bulky additional heat
sinks are required.
If a low profile design is not required
small electrolytic capacitors can be used
reducing the overall converter cost.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
! Fixed 175kHz Switching
Frequency
! Constant Frequency Voltage-
Mode Control Requires No
External Compensation
! Hiccup-Mode Over-Current
Protection
! High Efficiency
! Output Voltage Set By
Resistor Divider
! Under-Voltage Lockout
! Soft-Start And Enable
! Synchronous Rectification
! Small, 14-pin Surface Mount
Package
APPLICATIONS
! 12V to 3.3V Or Less Buck
Regulators
! 3.3/5V to 2.5V Or Less Buck
Regulators
! Hard Disk Drives
! Computer Add-on Cards
PRODUCT HIGHLIGHT - TYPICAL 12V TO 3.3V APPLICATION
12V
5V
10%
5%
R1
12V
165 Ohm
LM78L05
or equivalent
5V
TO
VCC
Optional 12V only circuit
R2
Css
100 Ohm _0.1µF
1
FB
2
NC
3
SS
4
CSP
5
GND
6
PGND
7
BDR
C5
1µF
14
VCC
13
NC ^RSET
12 3.3K
CS
11
NC
10
VC1
9
NC
8
TDR
C1
0.1µF
D1
5817SMT
3x
820µF, _C4
16V
Q1
SUB45N
05-20L
L1 is a powdered
iron toroid
Q2
SUB45N05-
20L
L1
10µH
4x
1500µF
6.3V
VOUT
3.3V
10A
C3
Copyright  2000
Rev. 1.0, 2001-09-19
PACKAGE ORDER INFO
T_A (°C)
OUTPUT
Plastic SOIC
D _14-PIN
0 to 70
Synchronous
LX1684CD
Note: Available in Tape & Reel.
Append the letter “T” to the part number. (i.e. LX1684CDT)
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
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