lx1675 Microsemi Corporation, lx1675 Datasheet - Page 16

• Manufacturer Part Number: lx1675
• Description: Multiple Output Loadshare?? Pwm Production Data Sheet
• Manufacturer: Microsemi Corporation

Copyright © 2004
Rev. 1.2a, 2006-02-16
LX1671 Product design Guide . The LX1675 and LX1671 have
the same functionality and this information will be applicable.
AN 18
the soft-start pin below 0.1V.
is the same as any of the other switching phases for control of its
output voltage shut down.
is compared to a 0.8V reference. The output voltage can be set to
any voltage above 0.8V (and lower than the input voltage) by
means of a resistor divider R1-R2 (see Figure 1).
error amplifier input current. Keep R
of magnitude).
O
P
ROGRAMMING
UTPUT
The LX1675 MOSFET driver outputs are shut off by pulling
The LDO voltage regulator has its own soft-start pin: SSL, that
The output voltage is sensed by the feedback pin (FB
Note: This equation is simplified and does not account for
For more information see Microsemi Application Note 1307:
TM
E
NABLE
T
HE
V
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
O
OUT
UTPUT
=
V
REF
V
OLTAGE
(1
+
1
R
and R
1
/R
A P P L I C A T I O N N O T E
2
)
2
close to 1kΩ (order
Integrated Products Division
Microsemi
X
®
) which
voltage (V
and receiver supply voltage (VDD).
requirement VDD is generally equal to VDDQ so that only V
VDDQ are required.
PWM phases. Since the currents for V
are quite often several amps, (2A to 6A is common) a switching
regulator is a logical choice
using the positive input of the phase 2 error amplifier RF2 as a
reference input from an external reference voltage V
defined as one half of VDDQ. Using V
will insure that all voltages are correct and track each other as
specified in the JEDEC (EIA/JESD8-9A) specification. The phase 2
output will then be equal to V
required.
functional for that phase
Termination for more details.
DDR V
Double Data Rate (DDR) SDRAM requires a termination
The LX1675 can supply both voltages by using two of the three
V
When an external reference is used the Soft Start will not be
See Microsemi Application Note 1306: DDR SDRAM Memory
Multiple Output LoadSHARE™ PWM
TT
( C O N T I N U E D )
for DDR memory can be generated with the LX1675 by
TT
TT
T
) in addition to the line driver supply voltage (VDDQ)
ERMINATION
P
RODUCTION
V
OLTAGE
REF
D
ATA
and track the VDDQ supply as
TT
S
REF
HEET
and (VDD plus VDDQ)
Although it is not a
as the reference input
REF
LX1675
which is
TT
and
Page 16