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NCP1203D100R2G Datasheet(PDF) 8 Page - ON Semiconductor |
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NCP1203D100R2G Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 14 page NCP1203 http://onsemi.com 8 Current−Mode Operation As the UC384X series, the NCP1203 features a well−known current mode control architecture which provides superior input audio−susceptibility compared to traditional voltage−mode controllers. Primary current pulse−by−pulse checking together with a fast over current comparator offers greater security in the event of a difficult fault condition, e.g. a saturating transformer. Adjustable Skip Cycle Level By offering the ability to tailor the level at which the skip cycle takes place, the designer can make sure that the skip operation only occurs at low peak current. This point guarantees a noise−free operation with cheap transformers. Skip cycle offers a proven mean to reduce the standby power in no or light loads situations. Wide Switching−Frequency Offer Four different options are available: 40 kHz − 65 kHz – 100 kHz. Depending on the application, the designer can pick up the right device to help reducing magnetics or improve the EMI signature before reaching the 150 kHz starting point. Overcurrent Protection (OCP) When the auxiliary winding collapses below UVLOlow, the controller stops switching and reduces its consumption. It stays in this mode until Vcc reaches 4.9 V typical, where the startup source is reactivated and a new startup sequence is attempted. The power supply is thus operated in burst mode and avoids any lethal thermal runaway. When the default goes way, the power supply automatically resumes operation. Wide Duty−Cycle Operation Wide mains operation requires a large duty−cycle excursion. The NCP1203 can go up to 80% typically. Low Standby Power If SMPS naturally exhibit 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 NCP1203 drastically reduces the power wasted during light load conditions. In no−load conditions, the NCP1203 allows the total standby power to easily reach next International Energy Agency (IEA) recommendations. No Acoustic Noise while Operating Instead of skipping cycles at high peak currents, the NCP1203 waits until the peak current demand falls below a user−adjustable 1/3rd of the maximum limit. As a result, cycle skipping can take place without having a singing transformer … You can thus select cheap magnetic components free of noise problems. External MOSFET Connection By leaving the external MOSFET external to the IC, you can select avalanche proof devices which, in certain cases (e.g. low output powers), let you work without an active clamping network. Also, by controlling the MOSFET gate signal flow, you have an option to slow down the device commutation, therefore reducing the amount of ElectroMagnetic Interference (EMI). SPICE Model A dedicated model to run transient cycle−by−cycle simulations is available but also an averaged version to help you closing the loop. Ready−to−use templates can be downloaded in OrCAD’s Pspice and INTUSOFT’s from ON Semiconductor web site, NCP1203 related section. Overload Operation In applications where the output current is purposely not controlled (e.g. wall adapters delivering raw DC level), it is interesting to implement a true short−circuit protection. A short−circuit actually forces the output voltage to be at a low level, preventing a bias current to circulate in the optocoupler LED. As a result, the auxiliary voltage also decreases because it also operates in Flyback and thus duplicates the output voltage, providing the leakage inductance between windings is kept low. To account for this situation and properly protect the power supply, NCP1203 hosts a dedicated overload detection circuitry. Once activated, this circuitry imposes to deliver pulses in a burst manner with a low duty−cycle. The system auto−recovers when the fault condition disappears. During the startup phase, the peak current is pushed to the maximum until the output voltage reaches its target and the feedback loop takes over. The auxiliary voltage takes place after a few switching cycles and self−supplies the IC. In presence of a short circuit on the output, the auxiliary voltage will go down until it crosses the undervoltage lockout level of typically 7.8 V. When this happens, NCP1203 immediately stops the switching pulses and unbias all unnecessary logical blocks. The overall consumption drops, while keeping the gate grounded, and the VCC slowly falls down. As soon as VCC reaches typically 4.8 V, the startup source turns−on again and a new startup sequence occurs, bringing VCC toward 12.8 V as an attempt to restart. If the default has gone, then the power supply normally restarts. If not, a new protective burst is initiated, shielding the SMPS from any runaway. Figure 15, on the following page, portrays the typical operating signals in short circuit. |
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