Current limit of MC33063A

Hello Team,

I understood the current-limit circuitry charge Ct, also limiting the amount of energy stored in the inductor.

MC33063A boost switching regulator is decreasing output voltage and maintain output current (C-C characteristic) during current limit.

Is my understanding correct?

I'm looking forward to hearing from you.

Best Regards,

Hidetoshi Matsunami

Hello Matsunami-san,

The Ipk pin input to the oscillator senses whether or not the current being pulled at the R sense resistor exceeds the desired maximum current.

If the current exceeds the desired maximum, then the CT charging current will increase, which will quickly end the current Ton pulse (turn off the switch). 

In the Boost configuration, the R sense resistor will always be able to sense the inductor current, so if the current limit is exceeded then no Ton pulse will occur. If no Ton pulse occurs, then the switch will not turn on and the Inductor will continue to draw current. In this case the output current will not be maintained but will drop (as the inductor discharges) until the R sense current is no longer exceeded, at which point the Ton pulses will resume.

Best,
Michael

Hello Michael,

Thank you for your reply.

Does the output voltage scale back linearly until the over-current if no Ton pulse occurs?

Also will the over-current flows from the input through inductor due to increasing of inductor current if Vin > Vout?

Best Regards,

Hidetoshi Matsunami

Hidetoshi-san,

For case where VIN > VOUT the pass diode will always provide uncontrolled current flow. Boost supplies in this topology need additional circuitry to protect against short circuits. The MC33063A only has control over the switch to ground.