CM6802A_12 Datasheet, PDF (17/25 Pages) Champion Microelectronic Corp. – EPA/80++ ZVS-Like PFC/PWM COMBO CONTROLLER

CM6802A/B/AH/BH (Dynamic Soft PFC/Green PWM)
http://www.championmicro.com.tw EPA/80++ ZVS-Like PFC/PWM COMBO CONTROLLER
Design for High Efficient Power Supply at both Full Load and Light Load
PFC Voltage Loop
There are two major concerns when compensating the
voltage loop error amplifier, V_EAO; stability and transient
response. Optimizing interaction between transient response
and stability requires that the error amplifier’s open-loop
crossover frequency should be 1/2 that of the line frequency,
or 23Hz for a 47Hz line (lowest anticipated international
power frequency).
The Current Loop Gain (S)
= ^ΔVISENSE * ^ΔDOFF * ^ΔIEAO
ΔDOFF ΔIEAO ΔISENSE
≈
VOUTDC * R_S
S * L * 2.5V
*
GM_I
*
ZCI
deviate from its 2.5V (nominal) value. If this happens, the
transconductance of the voltage error amplifier, GMv will
increase significantly, as shown in the Typical Performance
Characteristics. This raises the gain-bandwidth product of the
voltage loop, resulting in a much more rapid voltage loop
response to such perturbations than would occur with a
conventional linear gain characteristics.
The Voltage Loop Gain (S)
= ^ΔVOUT * ^ΔVFB * ^ΔVEAO
ΔVEAO ΔVOUT ΔVFB
≈
PIN* 2.5V
V2
OUTDC
*
ΔVEAO*
S
*
CDC
* GMV
*
ZCV
Z_CV: Compensation Net Work for the Voltage Loop
GM_v: Transconductance of VEAO
P_IN: Average PFC Input Power
V_OUTDC: PFC Boost Output Voltage; typical designed value is
380V.
C_DC: PFC Boost Output Capacitor
PFC Current Loop
The current transcondutance amplifier, GMi, I_EAO
compensation is similar to that of the voltage error amplifier,
V_EAO with exception of the choice of crossover frequency.
The crossover frequency of the
current amplifier should be at least 10 times that of
the voltage amplifier, to prevent interaction with the voltage
loop. It should also be limited to less than 1/6th that of the
switching frequency, e.g. 8.33kHz for a 50kHz switching
frequency.
Z_CI: Compensation Net Work for the Current Loop
GM_I: Transconductance of IEAO
V_OUTDC: PFC Boost Output Voltage; typical designed value is
380V and we use the worst condition to calculate the Z_CI
R_SENSE: The Sensing Resistor of the Boost Converter
2.5V: The Amplitude of the PFC Leading Edge Modulation
Ramp(typical)
L: The Boost Inductor
The gain vs. input voltage of the CM6802A/B/AH/BH’s voltage
error amplifier, V_EAO has a specially shaped non-linearity such
that under steady-state operating conditions the
transconductance of the error amplifier, GMv is at a local
minimum. Rapid perturbation in line or load conditions will cause
the input to the voltage error amplifier (V_FB) to
I_SENSE Filter, the RC filter between R_SENSE and I_SENSE :
There are 2 purposes to add a filter at I_SENSE pin:
1.) Protection: During start up or inrush current conditions, it will
have a large voltage cross Rs which is the sensing resistor
of the PFC boost converter. It requires the I_SENSE Filter to
attenuate the energy.
2.) To reduce L, the Boost Inductor: The I_SENSE Filter To reduce
L, the Boost Inductor: The I_SENSE Filter also can reduce the
Boost Inductor value since the I_SENSE Filter behaves like an
integrator before going I_SENSE which is the input of the
current error amplifier, IEAO.
The I_SENSE Filter is a RC filter. The resistor value of the I_SENSE
Filter is between 100 ohm and 50 ohm because I_OFFSET x the
resistor can generate an offset voltage of IEAO. By selecting
R_FILTER equal to 50 ohm will keep the offset of the IEAO less than
5mV. Usually, we design the pole of I_SENSE Filter at
fpfc/6=8.33Khz, one sixth of the PFC switching frequency.
Therefore, the boost inductor can be reduced 6 times without
disturbing the stability. Therefore, the capacitor of the I_SENSE
Filter, C_FILTER, will be around 381nF.
2012/05/10 Rev. 1.5
Champion Microelectronic Corporation
17