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PDF LX1660 Data sheet ( Hoja de datos )
| Número de pieza | LX1660 | |
| Descripción | ADVANCED PWM CONTROLLER | |
| Fabricantes | Microsemi Corporation | |
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T H E I N F I N I T E P O W E R O F I N N O VAT I O N
L I N D O C #: 1660
LX1660/1661
ADVANCED PWM CONTROLLER
PR O D U C T I O N D ATA S H E E T
DESCRIPTION
The LX1660 and LX1661 Are Mono-
lithic Switching Regulator Controller
ICs designed to provide low-cost, high-
performance adjustable power supply for
microprocessors and other applications
requiring a fast transient response and a
high degree of accuracy. They provide
an adjustable synchronous Pulse Width
Modulator output suitable for a power
supply for Pentium® or other micropro-
cessors.
Synchronous Rectifier Driver For
CPU Core. The devices can drive dual
MOSFETs resulting in typical efficiencies
of 85 - 90%, even with loads in excess of
10A. Synchronous shutdown results in
increased efficiency in light load applica-
tions.
Short-Circuit Current Limiting
Without Expensive Current Sense Re-
sistors. The current sensing mechanism
can use a PCB trace resistance or the para-
sitic resistance of the main inductor. For
applications requiring a high degree of
accuracy, a conventional sense resistor
can be used.
Hiccup Mode Fault Protection. The
hiccup mode is programmable and with
pulse-by-pulse current limiting will help
protect the power supply system and load
in the even of a short circuit.
Ultra-Fast Transient Response Re-
duces System Cost. The fixed frequency
modulated off-time architecture results in
the fastest transient response for a given
inductor. Adaptive voltage positioning
(LX1661 only) requires fewer low-ESR ca-
pacitors to meet stringent transient over-
and under-shoot specifications.
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
LX1661 IN SOCKET 7
PROCESSOR SUPPLY
APPLICATION
OUTEN
PRODUCT HIGHLIGHT
12V
KEY FEATURES
s Designed To Drive A Synchronous Rectifier
Stage — Can Also Be Used In Non-
Synchronous Applications
s Soft-Start Capability
s Hiccup-Mode Fault Protection
s No Current-Sense Resistor Required For
Current Limiting
s Modulated Constant Off-Time Control
Mechanism For Fast Transient Response And
Simple System Design
s 2V, 0.5% Internal Voltage Reference Brought
Out
A P P L I C AT I O N S
s Pentium Processor Supplies
s AMD-K6TM Supplies
s Cyrix® 6x86TM Supplies
s Voltage Regulator Modules
s General Purpose DC:DC Supplies
C2 C7
VIN 5V
R14, 1%
See Table 5
R15
2.0k
1%
R16
10k
C3
0.1µF
C4
390pF
C8
390pF
U1
LX1661
1 EN
2 OTADJ
3 SGND
4 VREF
5 INV
6 NINV
7 HICCUP
8 CT
VC1 16
TDRV 15
PGND 14
BDRV 13
VCC 12
SYNCEN 11
CS+ 10
CS- 9
16-pin SOIC
Q1
IRL3103
16V, 1000µF
Sanyo MV-GX or equivalent
VOUT
C9
1µF
L1
R1, 5m
5µH Toroid
C5 C6
D1
R5, 1k
C1
390pF
R6, 1k
16V, 1000µF
Sanyo MV-GX or
equivalent
Copyright © 1998
Rev. 1.1 7/98
PACKAGE ORDER INFORMATION
TA (°C)
N
Plastic DIP
16-pin
D
Plastic SOIC
16-pin
0 to 70
LX166xCN
LX166xCD
Note: All surface-mount packages are available in Tape & Reel.
Append the letter "T" to part number. (i.e. LX166xCDT)
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1
1 page  
PRODUCT DATABOOK 1996/1997
ADVANCED PWM CONTROLLER
PR O D U C T I O N D ATA S H E E T
LX1660/1661
FUNCTIONAL PIN DESCRIPTION
Pin # Description
EN 1 A low voltage at this pin puts the IC in sleep-mode.
OT ADJ
2 The purpose of this pin is to allow modulation of the OFF-time relative to the reference voltage. The OFF-time is
inversely proportional to the reference voltage. The inverting input of the upgrade voltage comparator is also
connected to this pin, when the voltage at this pin is below 0.7V, the controller shuts down.
SGND 3 This pin is the signal ground of the IC.
VREF 4 2V reference.
INV 5 This pin is the inverting input of the error comparator.
NINV/SS 6 This pin is the non-inverting input of the error comparator (LX1661 only: 40mV offset between this pin and error
comparator). This pin is pulled low during sleep-mode to allow soft-start function during start up.
HICCUP 7 A hiccup-mode capacitor connected to this pin adjusts duty cycle.
CT 8 The OFF-time is programmed by connecting a capacitor from this pin to ground.
CS- 9 This is the inverting input of the pulse-by-pulse current comparator.
CS+ 10 This is the non-inverting input of the pulse-by-pulse current comparator.
SYNCEN 11 This pin enables the synchronous (bottom) driver. A high voltage at this pin disables the synchronous driver.
VCC
BDRV
12 This is the IC supply voltage as well as the supply to the bottom MOSFET.
13 This is the gate drive to the bottom MOSFET
PGND 14 This is a separate ground for the top and bottom MOSFET.
TDRV 15 This is the gate drive to the top MOSFET.
VC1 16 This pin is a separate power supply input for the top drive.
Copyright © 1998
Rev. 1.1 7/98
5
5 Page 
PRODUCT DATABOOK 1996/1997
ADVANCED PWM CONTROLLER
PR O D U C T I O N D ATA S H E E T
LX1660/1661
USING THE LX1660/61 DEVICES
INPUT CAPACITOR
The input capacitor and the input inductor are to filter the
pulsating current generated by the buck converter to reduce
interference to other circuits connected to the same 5V rail. In
addition, the input capacitor provides local de-coupling of the
buck converter. The capacitor should be rated to handle the RMS
current requirement. The RMS current is:
IRMS = IL √ d(1-d)
CURRENT LIMIT (continued)
parasitic resistance of the inductor. One should include an RC
filter at the CS+ and CS- inputs, as shown in the Application
Information section, to eliminate jitter and noise.
For most applications, the resistors R5, R6 can be set at 1kΩ,
and C1 can be in the 300-500pF range as a starting point. If a fine
trim or adjustment of the current trip level is required, C1 may be
shunted by a resistor. C1 will introduce a small delay into the
current limit trip point, which effectively raises the threshold.
where IL is the inductor current and d is the duty cycle. The
maximum value, when d = 50%, IRMS = 0.5IL . For 5V input and
output in the range of 2 to 3V, the required RMS current is very
close to 0.5IL .
A high-frequency (ceramic) capacitor should be placed across
the drain of the top MOSFET and the source of the bottom one to
avoid ringing due to the parasitic inductor being switched ON and
OFF. See capacitor C7 in the Product Highlight on the first page
of this data sheet.
TIMING CAPACITOR SELECTION
The frequency of operation of the LX1660 / 1661 is a function of
the duty cycle and OFF-time. The OFF-time is proportional to the
timing capacitor (connected to Pin 8, CT ), and is modulated to
minimize frequency variations with duty cycle. The frequency is
constant, during steady-state operation, due to the modulation of
the OFF-time.
The timing capacitor (CT) should be selected using the follow-
ing equation:
CT =
(1 - VOUT / VIN ) * IDIS
fS (1.52 - 0.29 * VOUT )
where IDIS is fixed at 200µA and fS is the switching frequency
(recommended to be around 200kHz for optimal operation and
component selection).
When using a 5V input voltage, the switching frequency (fS) can
be approximated as follows:
CT = 0.621 *
IDIS
fS
Choosing a 680pF timing capacitor will result in an operating
frequency of 183kHz at VOUT = 2.8V. When a 12V power input is
used, the capacitor value must be changed (the optimal timing
capacitor for 12V input will be in the range of 1000 - 1500pF).
Sense Resistor
The current sense resistor (R1) is selected according to the for-
mula:
R1 = VTRIP / ITRIP
Where VTRIP is the current sense comparator threshold (100mV)
and ITRIP is the desired current limit. Typical choices are shown
below.
TABLE 2 - Current Sense Resistor Selection Guide
Load
Sense Resistor Value
Pentium-Class Processor (<10A)
Pentium II Class (>10A)
5mΩ
2.5mΩ
A smaller sense resistor will result in lower heat dissipation (I²R)
and also a smaller output voltage droop at higher currents.
There are several alternative types of sense resistor. The sur-
face-mount metal “staple” form of resistor has the advantage of
exposure to free air to dissipate heat and its value can be con-
trolled very tightly. Its main drawback, however, is cost. An alter-
native is to construct the sense resistor using a copper PCB trace.
Although the resistance cannot be controlled as tightly, the PCB
trace is very low cost.
PCB Sense Resistor
A PCB sense resistor should be constructed as shown in Figure
7. By attaching directly to the large pads for the capacitor and
inductor, heat is dissipated efficiently by the larger copper masses.
Connect the current sense lines as shown to avoid any errors.
Inductor
2.5mΩ Sense Resistor
100mil Wide, 850mil Long
2.5mm x 22mm (2 oz/ft2 copper)
CURRENT LIMIT
Current limiting occurs when a sensed voltage, proportional to
load current, exceeds the current-sense comparator threshold
value (90mV). The current can be sensed either by using a fixed
sense resistor in series with the inductor to cause a voltage drop
proportional to current, or by using a resistor and capacitor in
parallel with the inductor to sense the voltage drop across the
Output
Capacitor Pad
Sense Lines
FIGURE 7 — Sense Resistor Construction Diagram
Copyright © 1998
Rev. 1.1 7/98
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet LX1660.PDF ] | |
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