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LMR62014

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SNVS735B – OCTOBER 2011 – REVISED APRIL 2013

MAXIMUM SWITCH CURRENT

The maximum FET switch current available before the current limiter cuts in is dependent on duty cycle of the

application. This is illustrated in the graphs below which show typical values of switch current as a function of

effective (actual) duty cycle:

Figure 21. Switch Current Limit vs Duty Cycle

CALCULATING LOAD CURRENT

As shown in Figure 20 which depicts inductor current, the load current is related to the average inductor current

by the relation:

where

•

"DC" is the duty cycle of the application.

(7)

The switch current can be found by:

(8)

Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency:

(9)

combining all terms, we can develop an expression which allows the maximum available load current to be

calculated:

(10)

The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-OFF

switching losses of the FET and diode. For actual load current in typical applications, we took bench data for

various input and output voltages that displayed the maximum load current available for a typical device in graph

form:

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