Typical Performance Characteristics

9

Application Information: continued

Figure 6: The Sync pin generates a sync pulse at the beginning of each

The bi-directional SYNC pin can also receive an external

sync signal of a greater frequency. As show in Fig.7, when

the SYNC pin is triggered by an incoming signal, the IC

the steep falling edge, this valley voltage falls below the

the 0.95V(typ) Valley Clamp Voltage, the clamp is discon-

Figure 7: Operation with external sync. CH 2: SYNC pin, CH3: Gate pin,

Switch Frequency and Maximum Duty Cycle Calculations

the discharge time, the internal clock signal sets the Gate

output to the low state, thus providing a user selectable

maximum duty cycle clamp. Charge and discharge times

are determined by following general formulas;

,

where

Substituting in typical values for the parameters in the

above formulas:

0.57

0.57+ In

It is noticed from the equation that for the oscillator to

)

(

)

(

)

(

)

(

Design Guidelines