CL88020 datasheet(19/47 Pages) MICROCHIP

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 2017 Microchip Technology Inc.

DS50002611A-page 19

Figure 2-1 illustrates the connection between ADM00766 and ADM00767.

FIGURE 2-1:

Connection Diagram.

2.4

HOW DOES THE CL88020 120 VAC OFFLINE LED DRIVER EVALUATION

BOARD WORK?

The CL88020 120 VAC Offline LED Driver Evaluation Board is designed to control the

current through the four LED taps while maintaining high-input power factor (PF) and

low total harmonic distortion (THD). The CL88020 120 VAC Offline LED Driver Evalua-

tion Board includes a CL88020 IC, which is a sequential linear LED driver controlling

four taps. Tap sequencing assures the regulators are turned on and off at the proper

times. Tap sequencing also controls the smooth transition from one regulator to the

next without generating EMI-causing glitches in input current. Two concepts are

involved:

• The first is single-point control. All tap currents pass through a single control point.

This makes controlling overall input current easier than trying to control multiple

current paths.

• The second concept is called self-commutation. Using only the tap currents them-

selves, this technique inherently provides smooth transitions from one regulator to

the next without relying on tap voltages or the rectified AC to coordinate the transi-

tions. This avoids having to monitor high voltages and is more precise.

These two concepts work together to properly sequence the current regulators and to

provide glitch-free operation and thus avoiding conducted EMI.

The CL88020 120 VAC Offline LED Driver Evaluation Board and the CL88020 LED

Load Board contain all the circuitry necessary to perform, as well as overtemperature

protection (OTP), active line regulation (ALR) and output light ripple reduction.

The OTP protection operates linearly, gradually reducing output power as temperature

increases. This uses an inexpensive, external NTC thermistor to remotely sense LED

temperature. The thermistor is located on the LED load board, ADM00767, in close

proximity to the LEDs, providing near-direct LED temperature monitoring. The OTP

temperature is adjustable via selection of NTC resistance.

The ALR circuit maintains fairly constant output power over variations in AC line volt-

age. It is not a closed loop system that directly monitors and corrects output power.

Instead, it monitors the average voltage applied to the LED string and uses it to adjust

the reference voltage provided to the tap current regulators.

CL88020 Datasheet(PDF) 19 Page - Microchip Technology