CM6800AGIP datasheet(11/18 Pages) CHAMP

11 / 18 page

CM6800A

LOW START-UP CURRENT PFC/PWM CONTROLLER COMBO

2006/10/11 Rev. 1.3

Champion Microelectronic Corporation

Page 11

ZCI: Compensation Net Work for the Current Loop

GMI: Transconductance of IEAO

VOUTDC: PFC Boost Output Voltage; typical designed value

is 380V and we use the worst condition to calculate the ZCI

RS: The Sensing Resistor of the Boost Converter

2.5V: The Amplitude of the PFC Leading Modulation Ramp

L: The Boost Inductor

There is a modest degree of gain contouring applied to the

transfer characteristic of the current error amplifier, to

increase

its

speed

response

current-loop

perturbations. However, the boost inductor will usually be

the dominant factor in overall current loop response.

Therefore, this contouring is significantly less marked than

that of the voltage error amplifier. This is illustrated in the

Typical Performance Characteristics.

ISENSE Filter, the RC filter between RS and ISENSE :

There are 2 purposes to add a filter at ISENSE 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 ISENSE Filter to attenuate

the energy.

2.) To reduce L, the Boost Inductor: The ISENSE Filter

also can reduce the Boost Inductor value since the

ISENSE Filter behaves like an integrator before going

ISENSE which is the input of the current error

amplifier, IEAO.

The ISENSE Filter is a RC filter. The resistor value of the ISENSE

Filter is between 100 ohm and 50 ohm because IOFFSET x the

resistor can generate an offset voltage of IEAO. By selecting

RFILTER equal to 50 ohm will keep the offset of the IEAO less

than 5mV. Usually, we design the pole of ISENSE Filter at

fpfc/6, 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 ISENSE Filter,

CFILTER, will be around 283nF.

Figure 2. Compensation Network Connections for the

Voltage and Current Error Amplifiers

Figure 3. External Component Connections to VCC

CM6800AGIP Scheda tecnica(PDF) 11 Page - Champion Microelectronic Corp.

CM6800AGIP Scheda tecnica(HTML) 11 Page - Champion Microelectronic Corp.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Scheda tecnica Scarica

Link URL