onsemi NCP1250ASN65T1G

The NCP1250 is a highly integrated PWM controller capable of delivering a rugged and high performance offline power supply in a tiny TSOP−6 or PDIP−8 package. With a supply range up to 28 V, the controller hosts a jittered 65 kHz or 100 kHz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to a minimum level of 26 kHz. As the power further goes down, the part enters skip cycle while limiting the peak current. Over Power Protection (OPP) is a difficult exercise especially when no−load standby requirements drive the converter specifications. The ON proprietary integrated OPP lets you harness the maximum delivered power without affecting your standby performance simply via two external resistors. An Over Voltage Protection input is also combined on the same pin and protects the whole circuitry in case of optocoupler failure or adverse open loop operation. Finally, a timer−based short−circuit protection offers the best protection scheme, letting you precisely select the protection trip point irrespective of a loose coupling between the auxiliary and the power windings. The NCP1250 implements a standard current mode architecture where the switch−off event is dictated by the peak current setpoint. This component represents the ideal candidate where low part−count and cost effectiveness are the key parameters, particularly in low−cost ac−dc adapters, open−frame power supplies etc. Capitalizing on the NCP120X series success, the NCP1250 packs all the necessary components normally needed in today modern power supply designs, bringing several enhancements such as a non−dissipative OPP. Current−mode operation with internal ramp compensation: Implementing peak current mode control at a fixed 65 kHz or 100 kHz, the NCP1250 offers an internal ramp compensation signal that can easily by summed with the sensed current. Sub harmonic oscillations are eliminated via the inclusion of a single resistor in series with the current−sense information. Internal OPP: By routing a portion of the negative voltage present during the on−time on the auxiliary winding to the dedicated OPP pin, the user has a simple and non−dissipative means to alter the maximum peak current setpoint as the bulk voltage increases. If the pin is grounded, no OPP compensation occurs. If the pin receives a negative voltage down to -250 mV, then a peak current reduction down to 31.3% typical can be achieved. For an improved performance, the maximum voltage excursion on the sense resistor is limited to 0.8 V. Low startup current: Achieving a low no−load standby power always represents a difficult exercise when the controller draws a significant amount of current during start−up. Due to its proprietary architecture, the NCP1250 is guaranteed to draw less than 15 μA typical, easing the design of low standby power adapters.

• Fixed−Frequency 65 or 100 kHz Current−Mode Control Operation
• Internal and Adjustable Over Power Protection (OPP) Circuit
• Frequency Foldback Down to 26 kHz and Skip−Cycle in Light Load Conditions
• Internal Ramp Compensation
• Internal Fixed 4 ms Soft−Start
• 100 ms Timer−Based Auto−Recovery Short−Circuit Protection
• Frequency Jittering in Normal and Frequency Foldback Modes
• Option for Auto−Recovery or Latched Short−Circuit Protection
• OVP Input for Improved Robustness
• Up to 28 V VCC Operation
• +300 mA/ - 500 mA Source/Sink Drive Capability
• Less than 100 mW Standby Power at High Line
• EPS 2.0 Compliant
• These are Pb−Free Devices

• ac−dc Converters for TVs, Set−top Boxes and Printers
• Offline Adapters for Notebooks and Netbooks