IR3521

Page 32

V3.03

When a step load is applied, the capacitor acts as a short-circuit, at that instant, and pushes the OCSET signal up by

∆V (i.e. change in IIN) instantaneously. After an increase in its level, the OCP signal starts decaying exponentially

towards its original value. The rate of decay is determined by the RC time constant. The VR will enter hiccup mode

when the OCSET signal falls below the IIN value. The following equation (18) is use to calculate the ideal capacitor

value:

,

_

_

TDC

spike

OC

spike

OC

oc

spike

Spike

IDD

I

I

I

I

In

R

t

C











(18)

where,

= OC resistor (TDC),

= TDC OC Threshold,

Figure X:

Figure 20 Showing Dynamic OC Response

TDC

OC Threshold

IDD_Spike Boundary

IDD_Spike OC Threshold

tspike_oc

TDC

OC Threshold

IDD_Spike Boundary

IDD_Spike OC Threshold

tspike_oc