Pins and their functions

AN2934

14/27

Doc ID 15394 Rev 1

Figure 6.

Overload setpoint at 115 Vac

4.3

internal constant-current source inside the VIPer17HN. This pin is only enabled if the input

voltage is higher than 80 Vdc at the drain of the device. It is fixed and not dependent on the

shuts off the current source and starts switching. The charge current at start-up is 3 mA. If a

fault is detected, the charge current is reduced to 0.6 mA to obtain a slow duty cycle during

the restart phase and prevent overheating. The MOSFET is an 800 V minimum, avalanche-

start feature that progressively raises the drain current limitation to the maximum value as

shown in Figure 19. In this way, stresses on other components are considerably reduced.

4.4

Feedback pin

The feedback pin is the control input for duty cycle control. A voltage below 0.5 V activates

the burst mode operation. The upper level of 3.3 V borders on the cycle-by-cycle overcurrent

setpoint. For isolation this pin can be controlled by an optocoupler. The feedback point is

tied to 12 V in the single output reference design and to 5 V in the dual reference design. It

is normally tied before L2 to avoid a phase shift.

AM03423v1

OC trip VS Rlim

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

10

2030

405060

7080

R3 or Rlim