CS1600

DS904A7

7

4. INTRODUCTION

The CS1600 is a digitally controlled Power Factor Correction

(PFC) controller that operates in the Variable Frequency

Discontinuous Conduction Mode (VF - DCM). The CS1600

uses a proprietary digital algorithm to optimize control of the

power switch to deliver highly efficient performance for

electronic ballast applications. With this control scheme, the

total number of external components needed is minimized in

comparison to conventional control techniques, thus reducing

the overall system cost.

Digital control is achieved by constantly monitoring two voltages

that flow into the respective pins. These currents are then fed to

the inputs of two analog-to-digital converters (ADCs) and are

The digital outputs of the two ADCs are then processed in a

control algorithm which determines the behavior of the

CS1600 during start-up, normal operation, and under fault

conditions such as brownout, overvoltage, overcurrent,

overpower, and over-temperature. Details of operation during

these conditions are discussed in later sections of this

document.

Some of the key features of the CS1600 are as follows:

• Discontinuous Conduction Mode with Continuously

Variable Switching Frequency

The PFC switching frequency is varied every switching

cycle. This allows for a spread spectrum which minimizes

the conducted EMI peaks at any given frequency, thereby

minimizing the size and cost of the EMI filter required at

the front-end.

During start-up, the control algorithm limits the maximum

ON time and adjusts the frequency to avoid inductor sat-

uration and provides a near-trapezoidal envelope for the

input current during every half cycle. During normal oper-

ation, as the line voltage changes over half of a line cycle,

the frequency varies approximately 2:1 as shown in

Figure 7 below.

Figure 7. Switching Frequency vs. Phase Angle

Maximum power transfer occurs at the peak of the AC line

voltage, at which time, the frequency reaches its maxi-

mum value. Switching losses are minimized during peri-

ods of low power transfer by switching at lower

frequencies near the zero-crossing of the AC line.

This switching frequency profile helps reduce total BOM

cost through savings in the size of the boost inductor and

the EMI filter components, while at the same time, im-

proving overall system efficiency.

• Integrated Feedback Control

No external feedback compensation components are re-

quired for the CS1600. The internal digital control engine

self-compensates the feedback error signal using an

adaptive control algorithm.

• Protection Features

The CS1600 provides various protection features such as

undervoltage, overcurrent, overpower, open and short

circuit protection and brownout. It also provides the user

with the option of using the STBY pin to disable switching

of the device.

Rectified Line Voltage Phase (Deg.)

0

45

90

135

180

0

20

40

60

80

100

120

Line Voltage (% of Max)

Switching Frequency (% of Max)