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NCP1071 Datasheet(PDF) 11 Page - ON Semiconductor |
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NCP1071 Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 28 page NCP1070, NCP1071, NCP1072, NCP1075, NCP1076, NCP1077 http://onsemi.com 11 APPLICATION INFORMATION Introduction The NCP107x offers a complete current−mode control solution. The component integrates everything needed to build a rugged and low−cost Switch−Mode Power Supply (SMPS) featuring low standby power. The Quick Selection Table on page 2 details the differences between references, mainly peak current setpoints and operating frequency. • Current−mode operation: the controller uses current−mode control architecture. • 700 V Power MOSFET: Due to ON Semiconductor Very High Voltage Integrated Circuit technology, the circuit hosts a high *voltage power MOSFET featuring a 22/11/4.7 W RDS(on) – TJ = 25°C. This value lets the designer build a power supply up to respectively 7.75 W, 10 W and 15 W operated on universal mains. An internal current source delivers the startup current, necessary to crank the power supply. • Dynamic Self−Supply: Due to the internal high voltage current source, this device could be used in the application without the auxiliary winding to provide supply voltage. • Short circuit protection: by permanently monitoring the feedback line activity, the IC is able to detect the presence of a short−circuit, immediately reducing the output power for a total system protection. A tSCP timer is started as soon as the feedback current is below threshold, IFB(fault), which indicates the maximum peak current. If at the end of this timer the fault is still present, then the device enters a safe, auto−recovery burst mode, affected by a fixed timer recurrence, trecovery. Once the short has disappeared, the controller resumes and goes back to normal operation. • Built−in VCC Over Voltage Protection: when the auxiliary winding is used to bias the VCC pin (no DSS), an internal active clamp connected between VCC and ground limits the supply dynamics to VCC(clamp). In case the current injected in this clamp exceeds a level of 6.0 mA (minimum), the controller immediately stops switching and waits a full timer period (trecovery) before attempting to restart. If the fault is gone, the controller resumes operation. If the fault is still there, e.g. a broken opto−coupler, the controller protects the load through a safe burst mode. • Line detection: An internal comparator monitors the drain voltage as recovering from one of the following situations: ♦ Short Circuit Protection, ♦ VCC OVP is confirmed, ♦ UVLO ♦ TSD If the drain voltage is lower than the internal threshold (VHV(EN)), the internal power switch is inhibited. This avoids operating at too low ac input. This is also called brown−in function in some fields. • Frequency jittering: an internal low−frequency modulation signal varies the pace at which the oscillator frequency is modulated. This helps spreading out energy in conducted noise analysis. To improve the EMI signature at low power levels, the jittering remains active in frequency foldback mode. • Soft−Start: a 1 ms soft−start ensures a smooth startup sequence, reducing output overshoots. • Frequency foldback capability: a continuous flow of pulses is not compatible with no−load/light−load standby power requirements. To excel in this domain, the controller observes the feedback current information and when it reaches a level of IFBfold, the oscillator then starts to reduce its switching frequency as the feedback current continues to increase (the power demand continues to reduce). It can go down to 25 kHz (typical) reached for a feedback level of IFBfold(end) (100 mA roughly). At this point, if the power continues to drop, the controller enters classical skip−cycle mode. • Skip: if SMPS naturally exhibits a good efficiency at nominal load, they begin to be less efficient when the output power demand diminishes. By skipping un−needed switching cycles, the NCP107x drastically reduces the power wasted during light load conditions. |
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