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參數(shù)資料
| 型號： | LX1677CLQ |
| 英文描述： | PWM Controllers |
| 中文描述： | PWM控制器 |
| 文件頁數(shù)： | 18/21頁 |
| 文件大?。?/td> | 554K |
| 代理商： | LX1677CLQ |
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 18
Copyright
2000
Rev. 0.5i, 2002-07-17
W
M
.
C
LX1671
Multiple Output LoadSHARE PWM
P
RELIMINARY
I N T E G R A T E D P R O D U C T S
APPLICATION NOTE
(CONTINUED)
O
UTPUT
E
NABLE
The LX1671 MOSFET driver outputs are shut off by pulling
the soft-start pin below 0.3V.
The LDO voltage regulator has its own Enable/Disable pin
(LDDIS) for control of this output voltage.
P
ROGRAMMING
T
HE
O
UTPUT
V
OLTAGE
The output Voltage is sensed by the feedback pin (FB
X
) which
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).
)
/R
R
(1
V
V
2
1
REF
OUT
+
=
Note: This equation is simplified and does not account for
error amplifier input current. Keep R
1
and R
2
close to 1k
(order
of magnitude).
AN 18
For more information see Microsemi Application Note 18
LX1671 Product design Guide
DDR V
TT
T
ERMINATION
V
OLTAGE
Double Data Rate (DDR) SDRAM requires a termination
voltage (V
TT
)
in addition to the line driver supply voltage (VDDQ)
and receiver supply voltage (VDD). Although it is not a
requirement VDD is generally equal to VDDQ so that only V
TT
and VDDQ are required..
The LX1671 can supply both voltages by using two of the three
PWM phases. Since the currents for V
TT
and (VDD plus VDDQ)
are quite often several amps, (2A to 6A is common) a switching
regulator is a logical choice
V
TT
for DDR memory can be generated with the LX1671 by
using the positive input of the phase 2 error amplifier RF2 as a
reference input from an external reference voltage V
REF
which is
defined as one half of VDDQ. Using V
REF
as the reference input
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
REF
and track the VDDQ supply as
required.
When an external reference is used the Soft Start will not be
functional for that phase
See Microsemi Application Note 17 for more details.
A
P
P
L
I
C
A
T
I
O
N
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