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参数资料
| 型号： | LX1673-09CLQ |
| 英文描述： | PWM Controllers |
| 中文描述： | PWM控制器 |
| 文件页数： | 11/21页 |
| 文件大小： | 554K |
| 代理商： | LX1673-09CLQ |
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
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
THEORY OF OPERATION
G
ENERAL
D
ESCRIPTION
The LX1671 is a voltage-mode pulse-width modulation
controller integrated circuit. The internal ramp generator
frequency is fixed to 300kHz. The device has external
compensation, for more flexibility of output current magnitude.
U
NDER
V
OLTAGE
L
OCKOUT
(UVLO)
At power up, the LX1671 monitors the supply voltage for
VCC, VCCL, and VCX (there is no requirement for sequencing
the supplies). Before all supplies reach their under-voltage lock-
out (UVLO) thresholds, the soft-start (SS) pin is held low to
prevent soft-start from beginning, the oscillator is disabled and
all MOSFETs are held off. There is an internal delay that will
filter out transients less that 1.5uSec.
S
OFT
-S
TART
Once the supplies are above the UVLO threshold, the soft-start
capacitor begins to be charged by the reference through a 20k
internal resistor. The capacitor voltage at the SS pin rises as a
simple RC circuit. The SS pin is connected to the error
amplifier’s non-inverting input that controls the output voltage.
The output voltage will follow the SS pin voltage if sufficient
charging current is provided to the output capacitor.
The simple RC soft-start allows the output to rise faster at the
beginning and slower at the end of the soft-start interval. Thus,
the required charging current into the output capacitor is less at
the end of the soft-start interval. A comparator monitors the SS
pin voltage and indicates the end of soft-start when SS pin
voltage reaches 95% of V
REF
.
O
VER
-C
URRENT
P
ROTECTION
(OCP)
AND
H
ICCUP
The LX1671 uses the R
DS(ON)
of the upper MOSFET, together
with a resistor (R
SET
) to set the actual current limit point. The
current sense comparator senses the MOSFET current 350nS
after the top MOSFET is switched on in order to reduce
inaccuracies due to ringing. A current source supplies a current
(I
SET
), whose magnitude is 50μA. The set resistor R
SET
is
selected to set the current limit for the application. R
SET
and VSX
should be connected directly at the upper MOSFET drain and
source to get an accurate measurement across the low resistance
R
DS(ON)
.
When the sensed voltage across R
DS(ON)
plus the set resistor
exceeds the 300mV, V
TRIP
threshold, the OCP comparator
outputs a signal to reset the PWM latch and to start hiccup mode.
The soft-start capacitor (C
SS
) is discharged slowly (10 times
slower than when being charged up by R
SS
). When the voltage
on the SS pin reaches a 0.2V threshold, hiccup finishes and the
circuit soft-starts again. During hiccup both MOSFETs for that
phase are held off.
If any phase is not used connect the VSX and VCX pins to
VCC, do not leave them floating.
Hiccup is disabled during the soft-start interval, allowing start
up with maximum current. If the rate of rise of the output voltage
is too fast, the required charging current to the output capacitor
may be higher than the limit-current. In this case, the peak
MOSFET current is regulated to the limit-current by the current-
sense comparator. If the MOSFET current still reaches its limit
after the soft-start finishes, the hiccup is triggered again. When the
output has a short circuit the hiccup circuit ensures that the
average heat generation in both MOSFETs and the average current
is much less than in normal operation,.
Over-current protection can also be implemented using a sense
resistor, instead of using the R
DS(ON)
of the upper MOSFET, for
greater set-point accuracy.
O
SCILLATOR
F
REQUENCY
An internal oscillator sets the switching frequency at 300kHz.
T
HEORY OF
O
PERATION FOR A
B
I
-P
HASE
, L
OAD
SHARE
CONFIGURATION
The basic principle used in LoadSHARE, in a multiple phase
buck converter topology is that if multiple, identical, inductors
have the same identical voltage impressed across their leads, they
must then have the same identical current passing through them.
The current that we would like to balance between inductors is
mainly the DC component along with as much as possible the
transient current. All inductors in a multiphase buck converter
topology have their output side tied together at the output filter
capacitors. Therefore this side of all the inductors have the same
identical voltage.
If the input side of the inductors can be forced to have the same
equivalent DC potential on this lead, then they will have the same
DC current flowing. To achieve this requirement, phase 1 will be
the control phase that sets the output operating voltage, under
normal PWM operation. To force the current of phase 2 to be
equal to the current of phase 1, a second feedback loop is used.
Phase 2 has a low pass filter connected from the input side of each
inductor. This side of the inductors has a square wave signal that
is proportional to its duty cycle. The output of each LPF is a DC
(+ some AC) signal that is proportional to the magnitude and duty
cycle of its respective inductor signal. The second feedback loop
will use the output of the phase 1 LPF as a reference signal for an
error amplifier that will compare this reference to the output of the
phase 2 LPF. This error signal will be amplified and used to
control the PWM circuit of phase 2. Therefore, the duty cycle of
phase 2 will be set so that the equivalent voltage potential will be
forced across the phase 2 inductor as compared to the phase 1
inductor. This will force the current in the phase 2 inductor to
follow and be equal to the current in the phase 1 inductor.
There are four methods that can be used to implement the
LoadSHARE feature of the LX1671 in the Bi-Phase mode of
operation.
A
P
P
L
I
C
A
T
I
O
N
S
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LX1673-09CLQ-TR | 制造商:Microsemi Corporation 功能描述:VOLT MODE PWM CNTRLR 0.8V TO 5.5V 1A 20MLPQ - Tape and Reel |
| LX1673-09CPW | 功能描述:IC REG DL BCK/LINEAR 20TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（2），线性（LDO）（1） 功能:任何功能 输出数:3 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:4.5 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:28-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:* 包装:带卷 (TR) 其它名称:ISL6402IVZ-TTR |
| LX1673-09CPW-TR | 制造商:Microsemi Corporation 功能描述:VOLT MODE PWM CNTRLR 0.8V TO 5.5V 1A 20TSSOP - Tape and Reel |
| LX1675 | 制造商:MICROSEMI 制造商全称:Microsemi Corporation 功能描述:Multiple Output LoadSHARE⑩ PWM PRODUCTION DATA SHEET |
| LX1675 EVAL KIT | 制造商:Microsemi Corporation 功能描述:PWM CONTROLLERS - Bulk |
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