Overview
The NCP1255BD65R2G is a current-mode PWM controller designed by onsemi, specifically tailored for offline flyback converter applications. This controller is part of the NCP125x family, which is known for its high-performance and reliability in building cost-effective and robust power supplies.
Similar to its counterparts in the NCP125x series, such as the NCP1252, the NCP1255BD65R2G offers advanced features that make it suitable for a wide range of power supply designs, particularly in the ATX and adapter markets.
Key Specifications
| Characteristics | Symbol | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Startup threshold at which driving pulses are authorized | VCC(on) | 9.4 | 13.1 | 14.9 | V |
| Minimum Operating voltage at which driving pulses are stopped | VCC(off) | 8.4 | 9 | 9.6 | V |
| Hysteresis between VCC(on) and VCC(min) | VCC(HYS) | 0.9 | 4.5 | 5.0 | V |
| Current Sense Voltage Threshold | VILIM | 0.92 | 1 | 1.08 | V |
| Leading Edge Blanking Duration | tLEB | - | 160 | - | ns |
| Oscillator Frequency | fOSC | 92 | 100 | 108 | kHz |
| Frequency Modulation in percentage of fOSC | fjitter | - | ±5 | - | % |
| Maximum operating frequency | fMAX | 500 | - | - | kHz |
| Maximum duty-cycle | DCmax | 76 | 80 | 84 | % |
Key Features
- Current Mode Control: Implements peak current-mode control topology, similar to UC384X, to build rugged power supplies.
- Adjustable Switching Frequency: The switching frequency can be precisely set between 50 kHz and 500 kHz using a resistor connected to ground.
- Frequency Jittering: Frequency jittering softens the EMI signature by spreading out peak energy within a band ±5% from the center frequency.
- Brown-Out Detection: Auto-recovery Brown-Out detection protects against low input voltages and improves converter safety.
- Gate Drive Clamping: Includes a low-loss clamping voltage to prevent the gate voltage from exceeding 15 V, suitable for most power MOSFETs.
- Soft-Start and Delayed Operation: Adjustable soft-start timer and delayed operation upon start-up via an internal fixed timer.
- Over Current Protection: Latched primary over current protection with a fixed delay, extended to 150 ms in E versions.
Applications
The NCP1255BD65R2G is designed for use in various power supply applications, including:
- ATX Power Supplies: Ideal for building cost-effective and reliable ATX power supplies.
- Adapter Market: Suitable for adapter designs requiring high efficiency and reliability.
- Offline Flyback Converters: Optimized for offline flyback converter topologies.
Q & A
- What is the typical switching frequency range of the NCP1255BD65R2G?
The switching frequency can be adjusted between 50 kHz and 500 kHz.
- How does the NCP1255BD65R2G protect against low input voltages?
It features auto-recovery Brown-Out detection to protect against low input voltages.
- What is the maximum duty cycle for the NCP1255BD65R2G?
The maximum duty cycle is up to 84% depending on the version.
- How does the frequency jittering feature work?
Frequency jittering softens the EMI signature by spreading out peak energy within a band ±5% from the center frequency.
- What is the purpose of the gate drive clamping feature?
The gate drive clamping feature prevents the gate voltage from exceeding 15 V, which is suitable for most power MOSFETs.
- Does the NCP1255BD65R2G have built-in over current protection?
Yes, it has latched primary over current protection with a fixed delay.
- How is the soft-start duration adjusted?
The soft-start duration is adjusted using a capacitor connected to the SSTART pin.
- What is the typical supply voltage range for the NCP1255BD65R2G?
The VCC pin accepts a voltage range from 8 V to 28 V.
- Is there any delay before starting the soft-start when VCC(on) is reached?
Yes, there is an internal delay before starting the soft-start for A, B, and C versions, but no delay for D and E versions.
- What is the package type of the NCP1255BD65R2G?
The component is available in an SOIC-8 package.
