MC33066DW View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

MC33066DW

High Performance Resonant Mode Controllers

ON Semiconductor 

MC34066, MC33066

The maximum oscillator frequency is set by resistor RVFO

in a similar fashion using Equations 1 and 3 in Equation 5:

1

fOSC(max)

= tdchg(min) + tchg

(5)

The value chosen for resistor RDT will affect the peak

voltage of the oscillator waveform. As RDT is increased

from zero, the time required to charge COSC becomes large

with respect to the propagation delay through the oscillator

comparator. Consequently, the overshoot of the upper

threshold is reduced and the peak voltage on the oscillator

waveform drops from 5.1 V to 4.9 V. The best frequency

accuracy is achieved when RDT is zero ohms.

One−Shot Timer

The One−Shot capacitor CT is charged concurrently with

the oscillator capacitor by transistor Q1, as shown in

Figure 3. The One−Shot period begins when the oscillator

comparator turns off Q1, allowing CT to discharge. The

period ends when resistor RT discharges CT to the threshold

of the One−Shot comparator. Discharging CT from an initial

voltage of 5.1 V to a threshold voltage of 3.6 V results in the

One−Shot period given by Equation 6.

tOS = RT CT In

5.1

3.6

= 0.348 RT CT

(6)

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6

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