Charge Pump, Voltage Regulator, and Gate Driver
General Device Operation
The difficult function of startup is accomplished by using the trickle charging of a capacitor until an under voltage lock out circuit determines the voltage has reached approximately 14 volts. When this level is reached, a linear regulator is enabled to power the microprocessor, allowing it to boot up, and the MOSFET gate driver becomes active. Once the microprocessor is booted and the PFC MOSFET gate drive is operating, charge is pumped from the high voltage PFC circuit back through the VSUP pin, providing power for the microprocessor, gate driver, and any devices attached to the VCAP pin. The internal over voltage zener diode clamp limits the maximum Vcc to 17 volts. The block diagram of IXI858/859 is shown in Figure 1 below.
- VCC (pin 1) Power input from a high voltage source through a current limiting resistor and filter cap. 13V output when charge pump is active and is protected by UVLO Under Voltage Lock Out for low voltage conditions. This pin is clamped (Vclamp) for over-voltage protection by an internal zener diode at 17V.
- VOUT (pin 2) Linear regulated output at 3.3V for the IXI859 or 5V for the IXI858 and is typically used in providing power to a micro-controller.
- Pin 3 is not used.
- IN (pin 4) Used as an input signal to drive the output at pin 5, controlling a power MOSFET in a typical power factor correction application.
- GATE (pin 5) Output for driving external power MOSFET
- GND (pin 6) Ground return.
- VSUP (pin 7) Charge pump input. Receives switching energy from RC and enables / disables charge pump output. Requires low ESR capacitor.
- VCAP (pin 8) Charge pump output to supply external power.