CS1500-FSZ datasheet(8/22 Pages) CIRRUS

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CS1500

DS849A7

Jul ?$shortyear>

CONFIDENTIAL

3.1 PFC Operating Frequency

One key feature of the CS1500 is its operating frequency

profile. Figure 10 illustrates how the frequency varies over half

cycle of the line voltage in steady-state operation. When

power is first applied to the CS1500, it first examines the line

voltage and adapts its operating frequency to the exposed line

voltage as shown in Figure 11. The operating frequency is

varied in about a 2-to-1 ratio from the peak to the trough.

During start-up the control algorithm limits the maximum on-

time, provides nearly square-wave envelop current within

every half line cycle by adjusting the operating frequency for

fast startup behavior.

Figure 10. Switching Frequency vs. Phase Angle

Figure 11. Switching Frequency vs. Output Power

Figure 11 illustrates how the operating frequency (as a

percentage of maximum frequency) changes with output

power and the peak of the line voltage. Burst mode (when Po

below 5%) will be discussed in a later section.

The CS1500 is designed to function as a DCM (discontinuous

conduction mode) controller, however it may operate in a

quasi-CRM operation mode near the peak periods. For

90~265VAC main input applications, PFC can be also

designed in quasi-CRM at a peak of 90VAC and full load as

shown in Figure 12.

Figure 12. DCM and quasi-CRM Operation with CS1500

3.2 Start-up vs. Normal Operation Mode

CS1500 has two discrete operation modes: Start-up and

Normal. Start-up mode will be activated when Vlink is less than

90% of nominal value and remains active until Vlink reaches

100% of nominal value, as shown in Figure 13. Startup mode

is activated during initial system power-up. Any Vlink drop to

less than 90% of nominal value, such as load change, can

cause the system to enter Start-up Mode until Vlink is brought

back into regulation.

Figure 13. Start-up and Normal Modes

3.3 Burst Mode

Burst mode is utilized to improve system efficiency when the

system output power (Po) is < 5% of nominal. Burst mode is

implemented by intermittently disabling the PFC over a full

half-line period cycle under light load conditions, as shown in

Figure 14.

100

120

045

135

180

Rectified Line Voltage Phase (Deg.)

Switching Freq. (% of Max.)

Line Voltage (% of Max.)

% PO max

Vin < 150 VAC

100

Vin > 150 VAC

DCM

Quasi CRM

DCM

Quasi CRM

DCM

ILB

t [ms]

IAC

t [ms]

Vlink

[V]

100%

90%

Normal

Mode

Normal

Mode

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