Overview
The MC33063A-Q1 device primarily consists of an internal temperature-compensated reference, a comparator,
an oscillator, a PWM controller with active current limiting, a driver, and a high-current output switch. The
MC33063A-Q1 device requires minimal external components to build converters in the boost, buck, and inverting
topologies.
Feature Description
The device includes the following components:
• Temperature-compensated reference voltage
• Oscillator
• Active peak-current limit
• Output switch
• Output voltage-sense comparator
Reference Voltage
The reference voltage is set at 1.25 V and is used to set the output voltage of the converter.
Current Limit
Current limit is accomplished by monitoring the voltage drop across an external sense resistor located in series
with VCC and the output switch. The voltage drop developed across the sense resistor is monitored by the
current-sense pin, Ipk. When the voltage drop across the sense resistor becomes greater than the preset value
of 330 mV, the current-limit circuitry provides an additional current path to charge the timing capacitor (CT)
rapidly, to reach the upper oscillator threshold and, thus, limiting the amount of energy stored in the inductor. The
minimum sense resistor is 0.2 W. Figure 7 shows the timing capacitor charge current versus current-limit sense
voltage. To set the peak current, Ipk = 330 mV/Rsense.
Current Limit of Typical Operation Waveforms
The output switch is an NPN Darlington transistor. The collector of the output transistor is tied to pin 1, and the
emitter is tied to pin 2. This allows the designer to use the MC33063 device in buck, boost, or inverter
configurations. The maximum collector-emitter saturation voltage at 1.5 A (peak) is 1.3 V, and the maximum
peak current of the output switch is 1.5 A. For higher peak output current, an external transistor can be used.
Figure 8 shows the typical operation waveforms.