Overview
The NCP1251CSN65T1G is a highly integrated current-mode PWM controller designed by onsemi for use in offline power supplies. This component is packaged in a compact TSOP-6 package and is capable of delivering high performance and ruggedness. It operates at a fixed switching frequency of 65 kHz and features advanced protection mechanisms and efficiency enhancements.
Key Specifications
| Parameter | Value | Unit |
|---|---|---|
| Switching Frequency | 65 kHz | |
| Supply Voltage Range | Up to 28 V | V |
| Maximum Duty Cycle | 80% | |
| Frequency Jittering | ±5% of fOSC | |
| Maximum Junction Temperature | 150°C | °C |
| Storage Temperature Range | -60 to +150°C | °C |
| ESD Capability (Human Body Model) | 2 kV | |
| ESD Capability (Machine Model) | 200 V | |
| ESD Capability (Charged Device Model) | 1 kV | |
| Thermal Resistance Junction-to-Air | 360 °C/W | |
| Start-up Current | < 15 µA | µA |
| Internal IC Consumption | 1.4 to 2.2 mA | mA |
Key Features
- Current-Mode Operation with Internal Ramp Compensation: The NCP1251 operates in peak current mode control at a fixed 65 kHz, with an internal ramp compensation signal to eliminate sub-harmonic oscillations.
- Internal Over Power Protection (OPP): A non-dissipative OPP mechanism adjusts the maximum peak current setpoint based on the bulk voltage, using a simple resistive divider on the auxiliary winding.
- Low Startup Current: The controller draws less than 15 µA during startup, facilitating the design of low standby power adapters.
- EMI Jittering: An internal low-frequency modulation signal helps in spreading out energy in conducted noise analysis, improving the EMI signature.
- Frequency Foldback Capability: The controller reduces its switching frequency to a minimum level of 26 kHz under light-load conditions to improve efficiency.
- Latched Over Voltage Protection (OVP) on VCC: The controller monitors the VCC level and latches off when the voltage exceeds 25 V, maintaining VCC at 7 V until the power supply is unplugged.
- Short-Circuit Protection: The controller implements short-circuit and over-load protections using an internal timer and error flag, with some versions offering auto-recovery mode.
Applications
The NCP1251CSN65T1G is particularly suited for low-cost AC-DC adapters, open-frame power supplies, and other applications where low part-count and cost-effectiveness are key parameters.
Q & A
- What is the switching frequency of the NCP1251CSN65T1G?
The switching frequency of the NCP1251CSN65T1G is 65 kHz.
- What is the maximum supply voltage range for the NCP1251CSN65T1G?
The maximum supply voltage range is up to 28 V.
- How does the NCP1251CSN65T1G handle over power protection?
The NCP1251CSN65T1G features an internal non-dissipative OPP mechanism that adjusts the maximum peak current setpoint based on the bulk voltage.
- What is the startup current of the NCP1251CSN65T1G?
The startup current is less than 15 µA.
- How does the NCP1251CSN65T1G improve EMI performance?
The controller uses internal low-frequency modulation to jitter the oscillator frequency, improving the EMI signature.
- What is the frequency foldback capability of the NCP1251CSN65T1G?
The controller reduces its switching frequency to a minimum level of 26 kHz under light-load conditions to improve efficiency.
- How does the NCP1251CSN65T1G protect against over voltage on the VCC pin?
The controller latches off when the VCC voltage exceeds 25 V and maintains VCC at 7 V until the power supply is unplugged.
- What kind of short-circuit protection does the NCP1251CSN65T1G offer?
The controller implements short-circuit and over-load protections using an internal timer and error flag, with some versions offering auto-recovery mode.
- What are the typical applications for the NCP1251CSN65T1G?
The NCP1251CSN65T1G is suited for low-cost AC-DC adapters, open-frame power supplies, and other similar applications.
- What is the thermal resistance junction-to-air for the NCP1251CSN65T1G?
The thermal resistance junction-to-air is 360 °C/W.
- What is the maximum junction temperature for the NCP1251CSN65T1G?
The maximum junction temperature is 150°C.
