參數(shù)資料
型號(hào)： SC4901
廠商： Semtech Corporation
英文描述： COMBI-SYNC Secondary Side Synchronous Rectifier and Regulator
中文描述： 客貨兩用，同步二次側(cè)同步整流和穩(wěn)壓器
文件頁(yè)數(shù)： 19/20頁(yè)
文件大?。?/td> 598K
代理商： SC4901
19
2005 Semtech Corp.
www.semtech.com
SC4901
POWER MANAGEMENT
Application Information (Cont.)
Features and Applications of the Combi Sync Circuit
with SC4901
OUTPUT1
OUTPUT2
OUTPUT N
QS1
DSN
QR1
DS1
C2
DS2
L1
QRN
QFN
QR2
DRN
C1
QF1
QF2
DR2
QSN
DFN
QS2
DR1
DF1
LN
L2
DF2
CN
GATE DRV2
GATE DRV1
GATE DRV N
The Combi Sync topology is quite versatile and has a
number of useful features
a) There is no connection between primary and secondary
sides. No synchronising signals, drive pulses, voltage or
current information needs to be exchanged across the
isolation boundary. The bias supply for the controller is
also generated on the secondary side, eliminating the
additional burden of a low power bias supply. SC4901 is
designed to operate over a range of 4.5V to 18V AVCC
supply which is the typical range for MOSFET gate drives.
b) For multiple secondary windings, each winding can have
its own set of synchronous MOSFETs and each set can be
controlled by an individual SC4901 to generate
independently regulated outputs. There is no cross
regulation or minimum load requirement, each output can
be turned ON or OFF independently of others. Placing the
controller on the secondary side also helps to optimise
the transient response.
c) It is possible to have multiple sets of synchronous FETs
attached to the same transformer secondary and control
them individually as shown in Fig 12. This way multiple
secondary outputs with a common ground can be regulated
off the same secondary winding.
d) All secondary switching is synchronised automatically
with the transformer waveform. There is only one switching
frequency in the convertor which simplifies EMI filter
design. Zero current switching of the primary FET further
reduces the switching noise generated on the primary side.
e) A number of options can be used to generate and control
the transformer secondary voltage.
i) The primary may be free running, that is without being
regulated by a feedback loop. It may further employ
constant volt second operation to reduce magnetic
stresses. In this mode the duty cycle is always at an
optimum value to maximise the efficiency.
ii) The primary may be regulated in a feedback loop by one
of the outputs; such regulation will typically employ voltage
mode or average current mode control. Note that peak
current mode control is not suitable with the trailing edge
modulation.
Fig 12) Generating Multiple Outputs from the same
secondary winding using Combi Sync Topology
f) It is necessary to drive the forward FETs through a
transformer interface. The common source of the two
devices is a floating return and will swing to the peak
negative voltage appearing at the transformer secondary;
see the Vsec waveform in Fig 11). This negative swing
does not allow a semiconductor device to be used for
driving the forward FET pair. An additional pin called XFRA
is provided in SC4901 to simplify the design of driver
transformer interface, particularly with duty ratios of >50%.
XFRA is an open collector sink which turns on and off
simultaneously with OUTA.
g) The no load condition at the output needs special
consideration in this topology. Under light load, the inductor
current is negative as in any synchronous rectifier. When
the synchronous MOSFET QR is turned off, the current is
interrupted and tends to charge the drain source capacitor
of QR. The back to back connected forward FETs prevent
this current being returned to the source. The resulting
overshoot on QR can be clamped by connecting a zener
and diode combination across the inductor as shown in
Fig 4). The zener clamp conducts
only
during the dead
time and also provides a small benefit of reducing the
voltage across the forward FETs during turn on. The detailed
application schematic in Fig 4) shows diode D1 and zener
D2 connected across the output inductor L1 to reduce the
no load spike.
相關(guān)PDF資料
PDF描述
SC4901ITSTRT COMBI-SYNC Secondary Side Synchronous Rectifier and Regulator
SC4905A_06 High Performance Voltage Mode PWM Controller
SC4905AIMSTR High Performance Voltage Mode PWM Controller
SC4905AIMSTRT High Performance Voltage Mode PWM Controller
SC4905B High Performance Voltage Mode PWM Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC4901ITSTRT 制造商:Semtech Corporation 功能描述:Secondary Side PWM Cntrlr SYNC POST REGUL 1MHz 16-Pin TSSOP T/R 制造商:Semtech Corporation 功能描述:Controller IC
SC4905A 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:HIGH PERFORMANCE VOLTAGE MODE PWM CONTROLLER
SC4905A_06 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Voltage Mode PWM Controller
SC4905AIMSTR 制造商:Semtech Corporation 功能描述:IC, VOLTAGE MODE PWM CTRL, 12V, MSOP-10; Input Voltage:48V; Output Voltage:500mV; Output Current:1mA; Supply Voltage Min:0V; Supply Voltage Max:12V; Digital IC Case Style:MSOP; No. of Pins:10; Frequency:1MHz; Control Mode:Voltage ;RoHS Compliant: No
SC4905AIMSTRT 制造商:Semtech Corporation 功能描述:Voltage Mode PWM Controller 10-Pin MSOP T/R
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