CM6807(A;B;C)
10-PIN Green-Mode PFC/PWM Combo CONTROLLER for High Density AC Adapter
Functional Description
Detailed Pin Descriptions
The CM6807A consists of an ICST (Input Current Shaping
Technique), CCM (Continuous Conduction Mode) or DCM
(Discontinuous Conduction Mode) boost PFC (Power
Factor Correction) front end and a synchronized PWM
(Pulse Width Modulator) back end. The CM6807A is
designed to replace FAN6803 (8 pin SOP package), which
is the second generation of the ML4803 with 8 pin package.
It is distinguished from earlier combo controllers by its low
count, innovative input current shaping technique, and very
low start-up and operating currents. The PWM section is
dedicated to peak current mode operation. It uses
conventional trailing-edge modulation, while the PFC uses
IAC (Pin 2)
Typically, it has a feedforward resistor, RAC, 2KK~10KK ohm
resistor connected between this pin and rectified line input
voltage.
This pin serves 2 purposes:
1.) During the startup condition, it supplies the startup
current; therefore, the system does not requires
additional bleed resistor to start up the chip.
2.) The current of RAC will program the automatic
slope compensation for the system. This
feedforward signal can increase the signal to noise
ratio for the light load condition or the high input line
voltage condition.
leading-edge
modulation.
This
patented
Leading
Edge/Trailing Edge (LETE) modulation technique helps to
minimize ripple current in the PFC DC buss capacitor.
Optional Resistor between IAC and VCC:
This resistor is about 100K ohm, it can improve the THD of
the input current at high line and light load
The main improvements from ML4803 are:
1.
2.
Add Green Mode Functions for both PFC and PWM
Remove the one pin error amplifier and add back the
slew rate enhancement gmv, which is using voltage
input instead of current input. This transconductance
amplifier will increase the transient response 5 to 10
times from the conventional OP
ISENSE (Pin 3)
This pin ties to a resistor which senses the PFC input
current. This signal should be negative with respect to the IC
ground. It internally feeds the pulse-by-pulse current limit
comparator and the current sense feedback signal. The
ILIMIT trip level is –1V. The ISENSE feedback is internally
multiplied by a gain of four and compared against the internal
programmed ramp to set the PFC duty cycle. The
intersection of the boost inductor current downslope with the
internal programming ramp determines the boost off-time.
3.
4.
VFB PFC OVP comparator
PFC Tri-Fault Detect for UL1950 compliance and
enhanced safety
5.
A feedforward signal from IAC pin is added to do the
automatic slope compensation. This increases the
signal to noise ratio during the light load; therefore,
THD is improved at light load and high input line
voltage.
It requires a RC filter between ISENSE and PFC boost
sensing resistor.
6.
7.
CM6807A does not require the bleed resistor and it
uses the more than 800k ohm resistor between IAC
pin and rectified line voltage to feed the initial current
before the chip wakes up.
VINOK comparator is added to guaranteed PWM
cannot turn on until VFB reaches 2.5V in which PFC
boost output is about steady state, typical 380V.
A 10mS digital PWM soft start circuit is added
10 pin SOP package
VEAO (Pin 4)
This is the PFC slew rate enhanced transconductance
amplifier output which needs to connected with
compensation network Ground.
a
8.
9.
VFB (Pin 5)
Besides this is the PFC slew rate enhanced
transconductance input, it also tie to a couple of protection
comparators, PFCOVP, and PFC Tri-Fault Detect
10. No internal Zener but with VCCOVP comparator
The CM6807A operates both PFC and PWM sections at
67kHz. This allows the use of smaller PWM magnetic and
output filter components, while minimizing switching losses
in the PFC stage.
V + I (Pin 6)
This pin is tied to the primary side PWM current sense
resistor or transformer. It provides the internal pulse-by-pulse
current limit for the PWM stage (which occurs at 1.5V) and
the peak current mode feedback path for the current mode
control of the PWM stage. Besides current information, the
optocouple also goes into V + I pin. Therefore, it is the SUM
Amplifier input.
Several protection features have been built into the
CM6807A. These include soft-start, redundant PFC
overvoltage protection, PFC Tri-Fault Detect, VINOK, peak
current limiting, duty cycle limiting, under-voltage lockout,
reference ok comparator and VCCOVP.
Soft Start can be triggered by the following conditions:
1.) During the startup (VCC is less than 10V)
2.) DC to DC short (PWMtrifault is greater thanVCC-0.7V)
2006/10/11 Rev1.0
Champion Microelectronic Corporation
Page 7
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