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AOZ7111 Datasheet(PDF) 11 Page - Alpha & Omega Semiconductors |
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AOZ7111 Datasheet(HTML) 11 Page - Alpha & Omega Semiconductors |
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11 / 15 page  AOZ7111 Rev. 1.0 January 2013 www.aosmd.com Page 11 of 15 Figure 5. OVP Circuitry Around INV and OVP Pin AC Input Fault Detection AOZ7111 does not require an AC input voltage sensing, nor does it need the auxiliary winding with minus current detection. In general, the VCC of PFC controller is supplied by a system standby power supply, a mismatch may occur in a worst case scenario. A worst case scenario could be AC input chattering: the electric AC power source is suddenly absent for two or three additional AC line cycles, VCC is still higher than UVLO (VSTOP) during this time, so the voltage control loop tries to compensate for the VOUT drop and VCOMP will increase until it reaches its maximum clamp level. During the AC input recovery, high comp leads to very high switching current and severe stress is put on both the MOSFET and boost diode. To ensure that the system is more robust and reliable, AOZ7111 has a unique AC input fault detection circuit to protect against this type of scenario. If the AC input voltage is absent two or three additional cycles, internal soft-start is reset and waits for the AC input recovery again. During the AC input recovery, soft-start manages turn-on time allowing the switching current to increase smoothly. Figure 6. Operation with AC Input Fault Detection Under Voltage Lock Out (UVLO) UVLO function is used to prevent controller malfunction when VCC supply voltage drops. When VCC supply voltage reaches 12V (typ), the internal block of the IC is enabled and starts operation. When VCC supply voltage drops below 9.5V (typ), most of the internal circuit is disabled to reduce the IC current consumption. Under Voltage Protection (UVP) AOZ7111 detects the under voltage fault if VINV is less than VEN_INV. The UVP comparator disables the operation when VINV is less than 0.5V and there is 55mV hysteresis. An external small-signal MOSFET can be used to disables the IC. During disable mode, the current consumption of the IC decreases to 60µA or less. VCOMP IDS t t t VOUT VAC ROVP1 ROVP2 RFB1 RFB2 + 1.07*VREF + S Q R POR INV pin OVP pin VOUT 1.1*VREF |
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