CM6802A CHAMP [Champion Microelectronic Corp.], CM6802A Datasheet - Page 20

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

http://www.championmicro.com.tw
PWM Control (RAMP2)
generally used as the sampling point for a voltage
representing the current on the primary of the PWM’s 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 components
(R
and should have a peak value of approximately 5V. In voltage
mode operation, feed-forward from the PFC output buss is an
excellent way to derive the timing ramp for the PWM stage.
Soft Start (SS)
external capacitor at SS. A current source of 10
the charging current for the capacitor, and start-up of the
PWM begins at SS~1.4V. Start-up delay can be programmed
by the following equation:
where C
is the desired start-up delay.
allow the PFC time to generate sufficient output power for the
PWM section. The PWM start-up delay should be at least
5ms.
start capacitance value because premature charging of the
SS capacitor and activation of the PWM section can result if
VFB is in the hysteresis band of the 380V-OK comparator at
start-up. The magnitude of V
line voltage and nominal PFC output voltage. Typically, a
0.05
out to reach their nominal values prior to activation of the
PWM section at line voltages between 90Vrms and 265Vrms.
Generating V
voltage can vary from 10V to 17.9V. That’s the two ways to
generate VCC. One way is to use auxiliary power supply
around 15V, and the other way is to use bootstrap winding to
self-bias CM6802A/B/AH/BH system. The bootstrap winding
can be either taped from PFC boost choke or from the
transformer of the DC to DC stage. The ratio of winding
transformer for the bootstrap should be set between 18V and
15V.
2009/11/02
When the PWM section is used in current mode, RAMP2 is
Start-up of the PWM is controlled by the selection of the
It is important that the time constant of the PWM soft-start
Solving for the minimum value of C
Caution should be exercised when using this minimum soft
After turning on CM6802A/B/AH/BH at 13V, the operating
RAMP2
μ
C
C
SS
SS
F soft start capacitor will allow time for V
, C
SS
= 5ms x
= t
RAMP2
is the required soft start capacitance, and the t
DELAY
Rev. 1.4
),that will have a minimum value of zero volts
x
CC
10
1.8V
10
1.8V
μ
μ
A
A
Design for High Efficient Power Supply at both Full Load and Light Load
≒ 27nF
FB
at start-up is related both to
SS
:
CM6802A/B/AH/BH
Champion Microelectronic Corporation
EPA/80++ ZVS-Like PFC/PWM COMBO CONTROLLER
μ
FB
A supplies
and PFC
DEALY
bootstrap winding. The resistor of the filter can be set as
following.
R
I
PFC gate (pin 12) drive goes low and the PWM gate drive (pin
11) remains function. The resistor’s value must be chosen to
meet
CM6802A/B/AH/BH itself (5mA, max.) plus the current required
by the two gate driver outputs.
EXAMPLE:
and the CM6802A/B/AH/BH driving a total gate charge of 90nC
at 100kHz (e.g. 1 IRF840 MOSFET and 2 IRF820 MOSFET),
the gate driver current required is:
Choose R
1.0
capacitor of between 47
across the part, both for filtering and as part of the start-up
bootstrap circuitry.
Leading/Trailing Modulation
employ trailing edge modulation in which the switch will turn on
right after the trailing edge of the system clock. The error
amplifier output is then compared with the modulating ramp up.
The effective duty cycle of the trailing edge modulation is
determined during the ON time of the switch. Figure 4 shows a
typical trailing edge control scheme.
OP
FILTER
A filter network is recommended between VCC (pin 13) and
If anything goes wrong, and VCC goes beyond 19.4V, the
With a wanting voltage called, V
Conventional Pulse Width Modulation (PWM) techniques
The CM6802A/B/AH/BH should be locally bypassed with a
= 3mA (typ.)
μ
F ceramic capacitor. In most applications, an electrolytic
I
R
R
x I
GATEDRIVE
the
BIAS
BIAS
VCC
BIAS
(Dynamic Soft PFC/Green PWM)
=
=
~ 2V, I
= 214Ω
operating
5mA
V
18V
= 100kHz x 90nC = 9mA
BIAS
I
CC
VCC
+
−
+
−
15V
9mA
I
V
= I
G
CC
OP
μ
current
F and 220
+ (Q
PFCFET
BIAS
requirement
,of 18V, a VCC of 15V
+ Q
μ
F is also required
PWMFET
) x fsw
of
20
the