NCP1254: PWM Controller, Current Mode, for Offline Power Supplies

The NCP1254 is a highly integrated PWM controller capable of delivering a rugged and high performance offline power supply in a TSOP-6 package. With a supply range up to 35 V, the controller hosts a jittered 65-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 freezing the peak current setpoint. To help building rugged converters, the controller features several key protective features: a non-dissipative Over Power Protection for a constant maximum output current regardless of the input voltage, two latched over voltage protection inputs - either through a dedicated pin or via the Vcc input and a dual-level auto-recover/latched overload/short-circuit timer. The controller architecture is designed to authorize a transient peak power excursion when the current setpoint hits the limit. At this point, the switching frequency is increased form 65 kHz to 130 kHz until the peak event disappears. The timer duration is then modulated as the converter crosses a peak power excursion mode (long) or undergoes a short circuit (short).

Features
  • 65kHz Fixed Frequency Current Mode control with 130 kHz frequency excursion
  • Internal and adjustable Over Power Protection (OPP) circuit
  • Frequency Foldback down to 26 kHz and Skip-cycle in light load conditions
  • Timer-based Auto-recovery Overload/Short-circuit protection with 100% to 25% timer reduction for short-circuit faults
  • Frequency Jittering in Normal and Frequency Foldback Modes
  • Latch Input
  • Double Vcc hiccup in fault mode
Benefits
  • Allows peak power delivery without growing the transformer size by temporarily increasing the switching frequency
  • Compensates peak current for changing line conditions
  • Optimized efficiency across the entire power range
  • Robust protection against both overload and short circuit conditions
  • Softened EMI signature
  • Flexible input can be used for OVP or OTP protection
  • Reduced average power during fault mode
Applications
  • Ac-Dc adapters
End Products
  • Printer Power Supplies
  • Notebook Adapters
Data Sheets (1)
Document TitleDocument ID/SizeRevisionRevision Date
Current-Mode PWM Controller for Off-line Power SuppliesNCP1254/D (370.0kB)P1
Package Drawings (1)
Document TitleDocument ID/SizeRevision
TSOP-6318G-02 (64.1kB)V
Order Information
ProductStatusCompliancePackageMSL*ContainerBudgetary Price/Unit
NCP1254ASN65T1GActivePb-free Halide freeTSOP-6318G-021Tape and Reel3000$0.285
NCP1254BSN65T1GActivePb-free Halide freeTSOP-6318G-021Tape and Reel3000$0.285
Specifications
ProductTopologyControl Modefsw Typ (kHz)Stand-by ModeUVLO (V)Short Circuit ProtectionLatchSoft StartVCC Max (V)Drive Cap. (mA)
NCP1254ASN65T1GFlybackCurrent Mode65Yes8.8YesYesYes35300 / 500
NCP1254BSN65T1GFlybackCurrent Mode65Yes8.8YesYesYes35300 / 500
Current-Mode PWM Controller for Off-line Power Supplies (370.0kB) NCP1254
TSOP-6 STF202
NCP1254