lx1672 Microsemi Corporation, lx1672 Datasheet - Page 17

• Manufacturer Part Number: lx1672
• Description: Multiple Output Loadshare Pwm
• Manufacturer: Microsemi Corporation

Copyright © 2000
Rev. 1.0, 2005-08-10
voltage (V
(VDDQ) and receiver supply voltage (VDD). Although it is not a
requirement VDD is generally equal to VDDQ; so that only V
and VDDQ are required..
pulling the disable (DIS X ) pins above 1.2V.
for control of this output voltage. Pulling this pin above 3V
disables the LDO.
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).
O
P
Note: Keep R
DDR V
ROGRAMMING
UTPUT
The LX1672 PWM MOSFET driver outputs are shut off by
The LDO voltage regulator has its own Disable pin (LDDIS)
The output Voltage is sensed by the feedback pin (FB
Double Data Rate (DDR) SDRAM requires a termination
TM
TT
D
TT
ISABLE
T
ERMINATION
) in addition to the line driver supply voltage
1
and R
T
HE
V
2
O
OUT
close to 1kΩ (order of magnitude)
UTPUT
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=
V
V
OLTAGE
REF
V
OLTAGE
(1
+
R
1
/R
A P P L I C A T I O N N O T E
2
)
Integrated Products Division
X
®
) which
Microsemi
TT
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.
The LX1672 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 LX1672 by
P
RODUCTION
D
REF
ATA
and track the VDDQ supply as
TT
S
REF
HEET
and (VDD plus VDDQ)
as the reference input
REF
LX1672
which is
Page 17