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參數(shù)資料
| 型號： | SC4905BIMSTRT |
| 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 |
| 文件頁數(shù)： | 9/24頁 |
| 文件大?。?/td> | 378K |
| 代理商： | SC4905BIMSTRT |
SC4905A/B
POWER MANAGEMENT
Application Information (Cont.)
2006 Semtech Corp.
www.semtech.com
9
FEED FORWARD & MAXIMUM DUTY CYCLE
The feed forward function provided by the SC4905 will
improve the dynamic performance of the converter in
response to the changes in the input supply.
In voltage mode controllers without the voltage feed for-
ward circuitry, any changes in the input supply will cause
an error in the output voltage which is sensed by the error
amplifier and eventually is translated to an adjustment in
the duty cycle by the controller. This delay in the response
will cause the slower dynamic performance of the con-
verter.
This problem is resolved by sensing the input supply line
and making the adjustment in the duty cycle immediately
at the PWM controller.
R14
280k
C27
220p, 16V
R15
499k
Shut Down
Vin
R16
2k
R18
8.25k
U1
SC4905
4
5
3
2
10
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
The SC4905 uses the input supply line as the bias for
the oscillator circuitry, and the VFF pin. Any changes in
the line will cause the ramp peak voltage to be adjusted
to the VFF pin voltage while maintaining the oscillator
frequency unchanged.
The VFF pin can also be used to shut down the SC4905
if it is pulled down to GND by an open collector circuitry.
This can be useful for overvoltage protection or other
control signals.
The SC4905 also provides a programmable duty cycle,
that can be set by an external voltage divider from the
VFF pin. The ratio of the divider will determine the pro-
grammed duty cycle allowed.
VFF
VDMAX
%
DutyCycle
=
If the application does not require an upper limit on the
duty cycle, the VFF pin should be connected to the DMAX
pin. In this mode, the duty cycle will be allowed to increase
to the maximum limit of about 100%.
SYNC/Bi-Phase operation
In noise sensitive applications where synchronization of
the oscillator frequency to a reference frequency is re-
quired, the SYNC pin can accept the external clock.By
connecting an external control signal to the SYNC pin,
the Internal oscillator frequency will be synchronized to
the positive edge of the external control signal. SYNC is
a positive edge triggered input with a threshold set to
0.5*VFF.
In a single controller operation, SYNC chould be grounded
or connected to an external synchronization clock within
the SYNC frequency (see page 3).
Rosc2
VIN
Cosc1
Cosc2
U2
SC4905
4
5
3
2
10
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
Rosc1
U1
SC4905
4
5
3
2
10
1
6
7
8
9
DMAX
RC
VFF
FB
REF
VDD
SYNC
ILIM
GND
OUT
In the Bi-Phase operation mode a very unique oscillator
is utilized to allow two SC4905 to be synchronized
together and work out of phase. This feature is setup by
simple connection of the SYNC input to the RC pin of the
other part. The fastest oscillator automatically becomes
the master, forcing the two PWMs to operate out of
phase. This feature minimizes the input and output
ripples, and reduces stress on the capacitors.
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| SC4905A | High Performance Voltage Mode PWM Controller |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| SC4905BMSTR | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:HIGH PERFORMANCE VOLTAGE MODE PWM CONTROLLER |
| SC490AULTRT | 制造商:Semtech Corporation 功能描述:I2C BUCK CONTRO |
| SC490BULTRT | 制造商:Semtech Corporation 功能描述:DCDC power |
| SC4910A | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Secondary Side Controller with Synchronous Rectifier |
| SC4910AITSTR | 制造商:Semtech Corporation 功能描述:IC, PWM CONTROLLER, 12V, 20-TSSOP, Output Voltage:10V, Output Current:100mA, Sup |
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