LX1684_05 Datasheet, PDF (1/12 Pages) Microsemi Corporation – Voltage-Mode PWM Controller

LX1684
TM
®
Voltage-Mode PWM Controller
PRODUCTION DATA SHEET
DESCRIPTION
The LX1684 is a monolithic, voltage- Current is sensed using the voltage
mode pulse-width modulator controller. drop across the R_DS(ON) of the MOSFET
It is designed to implement a flexible, this sensing is delayed for 1µs to
low cost buck (step-down) regulator eliminate MOSFET ringing errors.
supply with a minimal of external Hiccup-mode fault protection reduces
components.
average power to the power elements
The LX1684 has a synchronous during short-circuit conditions.
driver for higher efficiency and is Under-voltage lockout and soft-start
optimized to provide 12V to 3.3V or are provided for optimal start-up
12V to 2.5V regulation. It also can be performance. Pulling the soft-start pin to
used to convert 5V or 3.3V to voltages ground can disable the LX1684.
as low as 1.25V.
The small 14-pin SOIC packaging,
Switching frequency is fixed at combined with low profile, low ESR
175kHz for optimal cost and space. capacitors, and TO-252 packaged FETs
Short-circuit current limiting can be results in a high efficiency converter in a
implemented without expensive current small board area. In most cases PCB
sense resistors.
copper can accomplish necessary heat
Similar to the LX1682 in function but sinking and no bulky additional heat
with the positive side of the current sinks are required.
sense comparator brought out (CSP) to If a low profile design is not required
allow it to be referenced to the topside small electrolytic capacitors can be used
FET.
reducing the overall converter cost.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
ƒ Fixed 175kHz Switching
Frequency
ƒ Constant Frequency Voltage-
Mode Control Requires No
External Compensation
ƒ Hiccup-Mode Over-Current
Protection
ƒ High Efficiency
ƒ Output Voltage Set By
Resistor Divider
ƒ Under-Voltage Lockout
ƒ Soft-Start And Enable
ƒ Synchronous Rectification
ƒ Small, 14-pin Surface Mount
Package
APPLICATIONS
ƒ 12V to 3.3V Or Less Buck
Regulators
ƒ 3.3/5V to 2.5V Or Less Buck
Regulators
ƒ Hard Disk Drives
ƒ 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
C5
1µF
1
FB
2
NC
3
SS
4
CSP
14
VCC
13
NC ^RSET
12 3.3K
CS
11
NC
5
10
GND VC1
6
9
PGND NC
7
8
BDR 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. 1.0c, 2005-03-08
PACKAGE ORDER INFO
T_A (°C)
0 to 70
OUTPUT
Synchronous
Plastic SOIC
D _14-PIN
RoHS Compliant / Pb-free Transition DC: 0440
LX1684CD
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1684CD-TR)
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
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