VOUT Pin Circuit

The secondary side of the InnoSwitch-3 is supplied from the main (regulated) output.  If this output is rated above 20V, the VOUT pin of the controller must be protected.  A voltage clamp as shown in Figure  1 below is recommended. Ideally VZ_VOUT = 20V should be used. The average current consumption of the VOUT pin does not exceed 10mA with peaks exceeding 100mA.  A T_VOUT with suitable voltage and current ratings should be chosen accordingly.

Figure  1:   VOUT pin Voltage Clamp (T_VOUT, R_VOUT and VZ_VOUT)

The resistance R_VOUT is calculated from Equation 1 below:

Equation 1:  Resistance calculation

Where I_Z is the Zener diode bias current; I_VOUT is the maximum current into the VOUT pin; and h_FE is the transistor T_VOUT common-emitter current gain.