AN2934

Comparison of EMI for single and dual output device with and without shield

Doc ID 15394 Rev 1

23/27

6.3

Soft-start

When the power supply starts, the output capacitors need to be charged up to the operating

voltage. During this initial time, the converter has to charge the output capacitors plus

deliver any output current required. This results in the maximum current being delivered to

the output. The maximum output current is proportional to the primary current limited by the

pulse-by-pulse current limit of the device. With the soft-start feature, the current’s trip level is

raised in 16 equal steps for a total duration of 8.5 ms. This prevents the current from

reaching a higher value during the start-up time. Figure 19 shows the soft-start feature of

the converter.

Figure 19.

Soft-start feature

AM03433v1