CS1500-FSZ datasheet(7/22 Pages) CIRRUS

7 / 22 page

CS1500

DS849A7

Jul ?$shortyear>

CONFIDENTIAL

3. INTRODUCTION

Figure 9. CS1500 Block Diagram

The CS1500 digital power factor controller operates in variable

on-time, variable frequency, discontinuous conduction mode

(DCM). The CS1500 uses a proprietary digital algorithm to

maximize the efficiency and reduce the conductive EMI.

The analog-to-digital converter (ADC) shown in the CS1500

block diagram in Figure 9 is used to sense the PFC output

voltage ( Vlink ) and the rectified AC line voltage ( Vrect ) by

measuring currents through their respective resistors. The

magnitudes of these currents are measured as a proportion of a

reference current (IREF) that functions as the reference for the

ADCs. The digital signal is then processed in a control algorithm

which determines the behavior of the CS1500 during start-up,

normal operation, and under fault conditions, such as brownout,

overvoltage, overcurrent, overpower, and over-temperature

conditions.

• DCM with Variable On-Time, Variable Switching Fre-

quency

The CS1500 PFC switching frequency varies with the

Vrect on a cycle-by-cycle basis, and its digital algorithm

calculates the on-time accordingly for unity power factor.

Unlike traditional Critical Conduction Mode (CRM) PFC

controller, CS1500 operates at its low switching frequen-

cy near the zero-crossing point of the AC input voltage,

even no switching at all, and it operates at its high switch-

ing frequency at the peak of its AC input voltage (this is

the opposite of the switching frequency profile for a CRM

PFC controller), thus CS1500 reduces switching losses

especially under light-load conditions, spreads conducted

EMI energy peaks over a wide frequency band and in-

creases overall system efficiency.

• Optimized Digital Loop Compensation

The proprietary digital control engine optimizes the feed-

back error signal using an adaptive control algorithm, im-

proves system stability and transient response. No

external feedback error signal compensation components

are required.

• Overcurrent Mitigation

The CS1500s digital controller algorithm limits the ON

time of the Power MOSFET by the following equation:

Where Ton is the max time that the power MOSFET is

turned on and Vrect is the rectified line voltage. In the

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.

• Over Voltage Protection

Under steady-state conditions, the voltage loop keeps

PFC output voltage close to its nominal value. Under light

load startup or feedback loop open conditions, the output

voltage may pass the overvoltage protection threshold.

The digital control engine initiates a fast response loop to

shut down gate driving signal to reduce the energy deliv-

ered to the output for PFC capacitor protection. When the

link voltage drop below VOVP-VOVP(Hy), PFC resumes

normal operation.

IAC

STBY

CS1500

VDD 7

NC 8

GND

Processor

Logic

NC 1

PWM

Driver

Oscillator

Protection

ADC

0.001126

rect

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