CM6802A CHAMP [Champion Microelectronic Corp.], CM6802A Datasheet - Page 19

• Manufacturer Part Number: CM6802A
• Description: EPA/80++ ZVS-Like PFC/PWM COMBO CONTROLLER
• Manufacturer: CHAMP [Champion Microelectronic Corp.]

http://www.championmicro.com.tw
Oscillator (RAMP1, or called RTCT)
fpwm=50Khz and fpfc=50Khz when VEAO=0V, it provides
the best performance in the PC application.
fpwm=100Khz and fpfc=50Khz when VEAO=0V, it provides
the best performance in the PC application.
The oscillator frequency, fRTCT is the similar formula in
CM6800:
following equation:
at VREF = 7.5V:
The dead time is so small (t
operating frequency can typically be approximately by:
Ct should be greater than 470pF.
standard components values, C
7.75kΩ
PWM Section
Pulse Width Modulator
The
straightforward, but there are several points which should
be
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.
2009/11/02
In CM6802A/AH, fRTCT=4xfpwm=4xfpfc fRTCT=200Khz,
In CM6802B/BH, fRTCT=2xfpwm=4xfpfc fRTCT=200Khz,
The dead time of the oscillator is derived from the
The dead time of the oscillator may be determined using:
Let us use 1000PF Solving for R
The dead time of the oscillator determined two things:
1.) PFC minimum off time which is the dead time
2.) PWM skipping reference duty cycle: when the PWM
noted.
fRTCT =
t
t
t
fRTCT =
RAMP
PWM
RAMP
DEADTIME
duty cycle is less than the dead time, the next cycle
will be skipped and it reduces no load consumption
in some applications.
= C
= C
Foremost
section
Rev. 1.4
=
T
T
t
t
x R
x R
RAMP
RAMP
4.216mA
1
2.5V
T
T
x In
x 0.51
+
1
t
DEADTIME
of
among
Design for High Efficient Power Supply at both Full Load and Light Load
V
V
x C
REF
REF
the
RAMP
T
−
−
= 593 x C
1.25
3.75
T
these
T
CM6802A/B/AH/BH
>> t
= 1000pF, and R
yields 7.75K. Selecting
DEADTIME
CM6802A/B/AH/BH
T
Champion Microelectronic Corporation
is
its
EPA/80++ ZVS-Like PFC/PWM COMBO CONTROLLER
) that the
inherent
T
is
=
In current-mode applications, the PWM ramp (RAMP2) 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 flowing in the converter’s output
stage. DCI
typically connected to RAMP2 in such applications. For
voltage-mode, operation or certain specialized applications,
RAMP2 can be connected to a separate RC timing network to
generate a voltage ramp against which V
Under these conditions, the use of voltage feed-forward from the
PFC buss can assist in line regulation accuracy and response. As
in current mode operation, the DC I
stage over-current protection.
CM6802A/B/AH/BH, as this function is generally performed on
the output side of the PWM’s isolation boundary. To facilitate the
design of opto-coupler feedback circuitry, an offset has been built
into the PWM’s RAMP2 input which allows V
zero percent duty cycle for input voltages below around 1.8V.
PWM Current Limit (DCILIMIT)
limiter for the PWM section. Should the input voltage at this pin
ever exceed 1V, the output flip-flop is reset by the clock pulse at
the start of the next PWM power cycle. Beside, the cycle-by-cycle
current, when the DC ILIMIT triggered the cycle-by-cycle current.
It will limit PWM duty cycle mode. Therefore, the power
dissipation will be reduced during the dead short condition.
CM6802A/B/AH/BH’s PWM section becomes a current mode
PWM controller. Sometimes, network between DCILIMIT and
RAMP2 is a resistor divider so the DCILIMIT’s 1V threshold can
be amplified to 1.5V or higher for easy layout purpose.
PWM Brown Out (380V-OK Comparator)
and inhibits the PWM if this voltage on V
2.36V. Once this voltage reaches 2.36V, which corresponds to
the PFC output capacitor being charged to its rated boost voltage,
the soft-start begins. It is a hysteresis comparator and its lower
threshold is 1.35V.
The DC I
When DCILIMIT pin is connected with RAMP2 pin, the
The 380V-OK comparator monitors the DC output of the PFC
No voltage error amplifier is included in the PWM stage of the
LIMIT
LIMIT
, which provides cycle-by-cycle current limiting, is
(Dynamic Soft PFC/Green PWM)
pin is a direct input to the cycle-by-cycle current
LIMIT
FB
input is used for output
is less than its nominal
DC
will be compared.
DC
to command a
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