Upper Threshold (1.25 V Typical)

Lower Threshold (0.75 V Typical)

Discharge

Time

V

Charge

6t

t

Comparator Output

Timing Capacitor, C

T

Output Switch

Nominal Output Voltage

Output Voltage

1

0

On

Off

Startup

Quiescent Operation

MC33063A-Q1

www.ti.com

SLLS654C – APRIL 2005 – REVISED DECEMBER 2014

Feature Description (continued)

Figure 8. Typical Operation Waveforms

7.4 Device Functional Modes

The oscillator is composed of a current source and a current sink that charge and discharge the external timing

capacitor (CT) between an upper and lower preset threshold. The typical charge current is 35 mA, and the typical

discharge current is 200 mA, yielding approximately a 6:1 ratio. Thus, the ramp-up period is six times longer than

that of the ramp-down period (see Figure 9). The upper threshold is 1.25 V, which is same as the internal

reference voltage, and the lower threshold is 0.75 V. The oscillator runs constantly, at a pace controlled by the

value of CT.

Figure 9. Oscillator Voltage Thresholds

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