LX1671CLQ-TR MICROSEMI [Microsemi Corporation], LX1671CLQ-TR Datasheet - Page 18

• Manufacturer Part Number: LX1671CLQ-TR
• Description: Multiple Output LoadSHARE PWM
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2000
Rev. 1.2b, 2006-02-13
LX1671 Product design Guide
AN 18
the soft-start pin below 0.3V.
(LDDIS) for control of this output voltage.
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 LX1671 MOSFET driver outputs are shut off by pulling
The LDO voltage regulator has its own Enable/Disable pin
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 18
TM
E
NABLE
T
HE
V
O
OUT
UTPUT
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=
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, Power Management
X
®
) which
Microsemi
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
DDR V
Double Data Rate (DDR) SDRAM requires a termination
The LX1671 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 17 for more details.
Multiple Output LoadSHARE™ PWM
TT
( C O N T I N U E D )
for DDR memory can be generated with the LX1671 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
LX1671
which is
TT
and
Page 18