CS1600

DS904A7

9

4.1.2

Burst Mode

In addition to the start-up mode and normal mode of operation,

the controller enters the burst mode of operation when the

During this stage, the PFC driver is disabled intermittently over

a full line cycle period, as shown in Figure 12. The period of

time for which the PFC drive is disabled depends on the level

of loading present..

Figure 12. Burst Mode of Operation

4.2

Input Feedforward and Output

Regulation

The CS1600 continuously monitors the rectified AC line and

the PFC output voltage through sense resistors tied to the IAC

and the FB pins to monitor the voltages, scaled as currents.

PFC output voltage. These currents are effectively compared

against an internal reference current to provide adaptive PFC

control. The resistor values are calculated as follows:

where

voltage

voltage

Figure 13. Output Feedback

Figure 14. Input Feedforward

4.3

Protection Features

4.3.1

Overvoltage Protection

threshold, as scaled by the current monitored by the sense

resistors, the CS1600 provides protection by disabling the

gate drive. A nominal hysteresis is provided to allow the

system to recover from the fault condition, before switching is

resumed.

4.3.2

Overcurrent Protection

The CS1600’s digital controller algorithm limits the ON

time of the Power MOSFET by the following equation:

event of a sudden line surge or sporadic, high dv/dt line

voltages, this equation may not limit the ON time appro-

priately. For this type of line disturbance, additional pro-

tection mechanisms, such as fusible resistors, fast-blow

fuses, or other current-limiting devices, are recommend-

ed.

[V]

t [ms]

Burst Mode

Active

[W]

t [ms]

5%

PFC

Disable

R

FB

V

link

V

DD

–

I

ref

-----------------------------

=

[Eq.1]

R

AC

R

FB

=

[Eq.2]

FB

VDD

ADC

7

15k

4

FB

VDD

ADC

7

15k

4

T

on

0.001126

V

rect

-------------------------

≤