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參數資料
型號： ML4800CP
廠商： Fairchild Semiconductor
文件頁數： 10/14頁
文件大小： 114K
描述： IC PFC CTRLR AVERAGE CURR 16DIP
標準包裝： 25
模式： 平均電流
頻率 - 開關： 76kHz
電流 - 啟動： 200µA
電源電壓： 11 V ~ 16.5 V
工作溫度： 0°C ~ 70°C
安裝類型： 通孔
封裝/外殼： 16-DIP（0.300"，7.62mm）
供應商設備封裝： 16-DIP
包裝： 管件
產品目錄頁面： 1222 (CN2011-ZH PDF)
其它名稱： ML4800CP_NL
ML4800CP_NL-ND
ML4800
PRODUCT SPECIFICATION
10
REV. 1.0.5 9/25/01
Oscillator (RAMP 1)
The oscillator frequency is determined by the values of R
T
 
and C
T
, which determine the ramp and off-time of the
oscillator output clock:
The dead time of the oscillator is derived from the following
equation:
at V
REF
 = 7.5V:
The dead time of the oscillator may be determined using:
The dead time is so small (tRAMP >> t
DEADTIME
) that the
operating frequency can typically be approximated by:
EXAMPLE:
For the application circuit shown in the data sheet, with the
oscillator running at:
Solving for R
T
 x C
T
 yields 1.96 x 10
-4
. Selecting standard
components values, C
T
 = 390pF, and R
T
 = 51.1k&.
The dead time of the oscillator adds to the Maximum PWM
Duty Cycle (it is an input to the Duty Cycle Limiter). With
zero oscillator dead time, the Maximum PWM Duty Cycle is
typically 45%. In many applications, care should be taken
that C
T
 not be made so large as to extend the Maximum Duty
Cycle beyond 50%. This can be accomplished by using a
stable 390pF capacitor for C
T
.
PWM SECTION
Pulse Width Modulator
The PWM section of the ML4800 is straightforward, but
there are several points which should be noted. Foremost
among these is its inherent synchronization to the PFC
section of the device, from which it also derives its basic
timing. The PWM is capable of current-mode or voltage
mode operation. In current-mode applications, the PWM
ramp (RAMP 2) is usually derived directly from a current
sensing resistor or current transformer in the primary of the
output stage, and is thereby representative of the current
owing in the converters output stage. DC I
LIMIT
, which
provides cycle-by-cycle current limiting, is typically con-
nected to RAMP 2 in such applications. For voltage-mode
operation or certain specialized applications, RAMP 2 can
be connected to a separate RC timing network to generate a
voltage ramp against which V
DC
 will be compared. Under
these conditions, the use of voltage feedforward from the
PFC buss can assist in line regulation accuracy and response.
As in current mode operation, the DC I
LIMIT
 input is used
for output stage overcurrent protection.
No voltage error amplier is included in the PWM stage of
the ML4800, as this function is generally performed on the
output side of the PWMs isolation boundary. To facilitate
the design of optocoupler feedback circuitry, an offset has
been built into the PWMs RAMP 2 input which allows V
DC
 
to command a zero percent duty cycle for input voltages
below 1.25V.
PWM Current Limit
The DC I
LIMIT
 pin is a direct input to the cycle-by-cycle
current limiter for the PWM section. Should the input
voltage at this pin ever exceed 1V, the output of the PWM
will be disabled until the output ip-op is reset by the clock
pulse at the start of the next PWM power cycle.
V
IN
 OK Comparator
The V
IN
 OK comparator monitors the DC output of the PFC
and inhibits the PWM if this voltage on V
FB
 is less than its
nominal 2.45V. Once this voltage reaches 2.45V, which
corresponds to the PFC output capacitor being charged to its
rated boost voltage, the soft-start begins.
PWM Control (RAMP 2)
When the PWM section is used in current mode, RAMP 2
is generally used as the sampling point for a voltage
representing the current in the primary of the PWMs output
transformer, derived either by a current sensing resistor or a
current transformer. In voltage mode, it is the input for a
ramp voltage generated by a second set of timing compo-
nents (R
RAMP2
, C
RAMP2
), that will have a minimum value of
zero volts and should have a peak value of approximately 5V.
In voltage mode operation, feedforward from the PFC output
buss is an excellent way to derive the timing ramp for the
PWM stage.
Soft Start
Start-up of the PWM is controlled by the selection of the
external capacitor at SS. A current source of 25礎 supplies
the charging current for the capacitor, and start-up of the
PWM begins at 1.25V. Start-up delay can be programmed by
the following equation:
f
OSC
1
t
RAMP
t
DEADTIME
+
--------------------------------------------------- -
=
(2)
t
RAMP
C
T
R
T
?/DIV>
In
V
REF
1.25

V
REF
3.75

----------------------------- -
?/DIV>
=
(3)
t
RAMP
C
T
R
T
?/DIV>
0.51
?/DIV>
=
t
DEADTIME
2.5V
5.5mA
---------------- -   C
T
?/DIV>
450  C
T
?/DIV>
=
=
(4)
f
OSC
1
t
RAMP
--------------- -
=
(5)
f
OSC
100kHz
1
t
RAMP
--------------- -
=
=
C
SS
t
DELAY
25礎
1.25V
-------------- -
?/DIV>
=
(6)
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相關代理商/技術參數
參數描述
ML4800CP 制造商:Fairchild Semiconductor Corporation 功能描述:IC PFC/PWM COMBO 4800 DIP16
ML4800CP_NL 功能描述:功率因數校正 IC Power Factor PWM Contrl 0.2mA 81KHz RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
ML4800CP_Q 功能描述:功率因數校正 IC PFC Controller PWM Combo RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
ML4800CS 功能描述:功率因數校正 IC PFC Controller PWM Combo RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
ML4800CS_Q 功能描述:功率因數校正 IC PFC Controller PWM Combo RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
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