參數(shù)資料
型號(hào)： SC4905A_06
廠商： Semtech Corporation
英文描述： High Performance Voltage Mode PWM Controller
中文描述： 高性能電壓模式PWM控制器
文件頁(yè)數(shù)： 10/24頁(yè)
文件大?。?/td> 378K
代理商： SC4905A_06
SC4905A/B
POWER MANAGEMENT
Application Information (Cont.)
2006 Semtech Corp.
www.semtech.com
10
FEED BACK
The error signal from the output of an external Error am-
plifier such as SC431 or SC4431 is applied to the invert-
ing input of the PWM comparator at the FB pin either
directly or via an opto coupler for the Isolated applica-
tions. For best stability keep the FB trace length as short
as possible.
C35
22n, 16V
R23
5.1k
Secondary Supply
C31
22pF
C30
NA
R25
100k
C36
4.7nF
Vref
U6
SC4431
1
2
4
5
REF
C33
680pF
Vout
C32
1nF
R24
3.74k
C34
0.1u,16V
R26
80.2k
R29
NA
MOCD207
1
2
8
7
3
4
6
5
0
FB
R27
9.1k
R22
1.1k
The signal at the FB pin is then compared to the ramp
signal from the RC pin and the OUT gate drive signal is
generated.
Voltages below 600mV at the FB pin, will produce a 0%
duty cycle at the OUT drive. Maximum duty cycle is pro-
duced when VFB-600mV>VFF. The FB signal range is from
600mv to 4V.
OVER CURRENT
A pulse by pulse current limit is provided by the SC4905.
The current information is sensed at the ILIM pin and
compared to a peak current limit level of 180mV. If the
180mV limit is exceeded, the OUT pulse is terminated.
GATE DRIVERS
OUT is a CMOS gate drive output stage that is supplied
from REF and provides a peak source/sink current of
about 1mA. The output stage is capable of driving the
logic input of external MOSFET Drivers and is switched at
the oscillator frequency. When the voltage on the RC pin
is rising,, the output is high.
It should be noted that if high speed/high current drivers
such as the SC1301 are used, careful layout must be
followed in order to minimize stary inductance, which
might cause negative voltages at the output of the driv-
ers. This negative voltage can be clamped to reasonable
level by placing a small Schottky diode directly at the
output of the driver as shown below.
VDD
U1
SC4905
4
5
3
2
10
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
C22
VDD
REF
Mosfet Gate
D11
U2
SC1301A
1
4
3
2
5
C18
D8
C17
R13
SOFT START
During start up of the converter, the discharged output
capacitor, and the load current demand large supply cur-
rent requirements. To avoid this a soft start scheme is
usually implemented where the duty cycle of the regula-
tor is gradually increased from 0% until the soft start
duration is elapsed.
Programmable soft start duration can implemented ex-
ternally by utilizing a simple external circuitry shown be-
low.
SC4905
U1
4
5
3
2
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
56.2K
Csoft start
REF
MOCD207
3
4
6
5
C30
R22
1.1k
Approximate soft start duration can be calculated as be-
low:
D11
D15
Rsense
C18
C17
U1
SC4905
4
5
3
2
10
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
M1
C22
R17
D7
D8
C26
VDD
VDD
R13
0
REF
R11
U2
SC1301A
1
4
3
2
5
R30
相關(guān)PDF資料
PDF描述
SC4905AIMSTR High Performance Voltage Mode PWM Controller
SC4905AIMSTRT High Performance Voltage Mode PWM Controller
SC4905B High Performance Voltage Mode PWM Controller
SC4905BIMSTR High Performance Voltage Mode PWM Controller
SC4905BIMSTRT High Performance Voltage Mode PWM Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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
SC4905AMSTR 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:HIGH PERFORMANCE VOLTAGE MODE PWM CONTROLLER
SC4905B 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Voltage Mode PWM Controller
SC4905BIMS.TR 制造商:Semtech Corporation 功能描述:
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