ZSLS7031 Datasheet

© 2016 Integrated Device Technology, Inc.

9

January 26, 2016

2

Circuit Description

Refer to the basic application circuit shown on page 2 for the external components referenced in the following

sections.

2.1

ZSLS7031 Overview

The ZSLS7031 consists of the basic functional blocks shown in Figure 2.1.

Figure 2.1

ZSLS7031 Block Diagram

2.2

Startup Voltage

After power is applied to the circuit, R3 provides a trickle current to allow C4 to begin charging. The ZSLS7031

(see specification 1.3.1).

The value of R3 and C4 can be determined by the input voltage. Choosing a larger value of R3 increases the

startup time but reduces the losses after the circuit is running. A low ESR capacitor of 2.2µF rated for 25V is

recommended for C4.

2.3

Soft Start Control

When the ZSLS7031 is initially powered up, the internal automatic gain control (AGC) output is at the minimum

value, so the peak CS threshold is initially much less than 0.5V. The AGC steps up cycle-by-cycle until the CS

threshold at the peak of the input sine wave is equal to 0.5V. With this technique, it will take several cycles of the

AC waveform for the final value of current to be attained, as shown in Figure 2.2.