參數(shù)資料
型號(hào)： SC4808B
廠商： Semtech Corporation
英文描述： High Performance Dual Ended PWM Controller
中文描述： 高性能雙端PWM控制器
文件頁(yè)數(shù)： 13/31頁(yè)
文件大?。?/td> 483K
代理商： SC4808B
13
2005 Semtech Corp.
www.semtech.com
SC4808A/B
POWER MANAGEMENT
Application Information
overcurrent comparators. An internal 1 to 3 feedback volt-
age divider provides a 3X amplification of the CS signal.
This is used for comparison to the external error amplifier
signal. If an external resistor is connected from CS to the
current sense resistor, the internal current source will pro-
vide a programmable slope compensation. The value of
the resistor will determine the level of compensation. At
higher compensation levels, voltage mode of operation can
be achieved. The error amplifier signal at the FB pin will be
used in conjunction with the CS signal to achieve regula-
tion.
Two levels of undervoltage lockout are also available. The
LUVLO (line under voltage lockout)
pin via an external re-
sistive divider will program the undervoltage lockout level.
During the LUVLO, the driver outputs are disabled and the
softstart is reset.
Once VCC has exceeded the UVLO (VCC under voltage lock-
out) limit, the internal reference, oscillator, drivers and logic
are powered up.
SYNC is a positive edge triggered input with a threshold
set to 1.6V (SC4808A), and 1.0V (SC4808B).
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. In a single con-
troller operation, SYNC should be grounded or connected
to an external synchronization clock within the SYNC fre-
quency range (see page 3).
In the Bi-phase operation mode a very unique oscillator
is utilized to allow two SC4808 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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THEORY OF OPERATION
The SC4808 is a versatile double ended, high speed, low
power, pulse width modulator that is optimized for applica-
tions requiring minimum space.
The device contains all of the control and drive circuity re-
quired for isolated or non isolated power supplies where
an external error amplifier is used. A fixed oscillator fre-
quency (up to 1MHz) can be programmed by an external
RC network.
The SC4808 is a peak current or voltage mode controller,
depending on the amount of slope compensation,
programmable with only one external resistor. The cycle by
cycle peak current limit prevents core saturation when a
transformer is used for isolation while the overcurrent
circuitry initiates the softstart cycle.
The SC4808 dual output drive stages are arranged in a
push-pull configuration. Both outputs switch at half the
oscillator frequency using a toggle flip flop. The dead time
between the two outputs is programmable depending on
the values of the timing capacitor and resistors, thus limiting
each output stage duty cycle to less than 50%.
The SC4808 also provides flexibility with programmable
LUVLO thresholds, with built-in hysteresis.
SUPPLY
A single supply, VCC is used to provide the bias for the
internal reference, oscillator, drivers, and logic circuitry of
SC4808.
PWM CONTROLLER
SC4808 is a double ended PWM controller that can be
used in voltage or current mode applications. Two voltage
options are available for the SC4808. The SC4808A ver-
sion has a typical VCC under voltage of 12.0V and a 5V
reference. The SC4808B version provides a 4.4V VCC UVLO,
and a 3.125V reference. The oscillator frequency is pro-
grammed by a resistor and a capacitor network connected
to an external reference provided by the SC4808. The two
outputs, OUTA and OUTB, are 180 degrees out of phase
and run at half of the oscillator frequency.
An external error amplifier will provide the error signal to
the FB pin of the SC4808.
The current sense input and internal slope compensation
are both provided via the CS pin. The current sense input
from a sense resistor is used for the peak current and
相關(guān)PDF資料
PDF描述
SC4808BIMSTR High Performance Dual Ended PWM Controller
SC4808BIMSTRT High Performance Dual Ended PWM Controller
SC4808B-1 High Performance Dual Ended PWM Controller
SC4808B-1MSTRT High Performance Dual Ended PWM Controller
SC4808B-2 High Performance Dual Ended PWM Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC4808B-1 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-1MSTRT 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2_09 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2MSTRT 制造商:Semtech Corporation 功能描述:Current Mode PWM Controller -0.5V to 18V 250mA 10-Pin MSOP T/R 制造商:Semtech 功能描述:Current Mode PWM Controller -0.5V to 18V 250mA 10-Pin MSOP T/R
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