Overview
The LM5021MM-2 is an AC-DC current-mode PWM controller produced by National Semiconductor, now part of Texas Instruments. This controller is designed for highly efficient off-line single-ended flyback and forward power converters. It features ultra-low startup current, making it suitable for energy-conserving applications. The LM5021MM-2 is available in an 8-pin VSSOP or PDIP package and operates over a wide temperature range of -40°C to 125°C.
Key Specifications
| Specification | Value |
|---|---|
| Package | 8-VSSOP, 8-PDIP |
| Operating Temperature | -40°C to 125°C |
| Startup Current | 25 µA (maximum) |
| Maximum Duty Cycle | 50% (LM5021-2) |
| Oscillator Frequency | Up to 1 MHz (programmable) |
| Gate Driver Current | 0.3 A (source), 0.7 A (sink) |
| Current Sense Threshold | 500 mV |
| Overcurrent Protection | Cycle-by-cycle, Hiccup mode for continuous overload |
| Soft-Start | Gradual start-up via external capacitor |
| Input Voltage Range | 90 ~ 264 Vac (for AC applications) |
Key Features
- Ultra-low Startup Current: 25 µA maximum, minimizing power losses in the high voltage start-up network.
- Current Mode Control: With cycle-by-cycle overcurrent protection and a 500 mV maximum current sense threshold.
- Skip Cycle Mode: Reduces power consumption at light loads for energy-conserving applications.
- Single Resistor Programmable Oscillator: Allows for adjustable switching frequency up to 1 MHz.
- Synchronizable Oscillator: Can be synchronized to an external clock source.
- Integrated 0.7-A Peak Gate Driver: With source/sink current capability.
- Direct Opto-Coupler Interface: For feedback and control.
- Maximum Duty Cycle Limiting: 50% for LM5021-2, ensuring precise duty cycle control.
- Soft-Start Capability: Gradual start-up to reduce start-up stresses and current surges.
- Undervoltage Lockout (UVLO) with Hysteresis: Protects against low input voltage conditions.
- Hiccup Mode for Continuous Overload Protection: Reduces component stresses during sustained overcurrent conditions.
Applications
The LM5021MM-2 is suitable for a variety of applications, including:
- Off-line Power Supplies: Single-ended flyback and forward converters.
- Energy-Efficient Systems: Applications requiring low standby power, such as ENERGY STAR®, CECP, and similar energy-conserving standards.
- High-Efficiency Power Converters: Where precise control over duty cycle and current is necessary.
- Consumer Electronics: Power supplies for TVs, computers, and other electronic devices.
- Industrial Power Systems: Where reliable and efficient power conversion is critical.
Q & A
- What is the maximum duty cycle of the LM5021-2?
The maximum duty cycle of the LM5021-2 is 50%.
- How is the oscillator frequency programmed in the LM5021MM-2?
The oscillator frequency is programmed using a single external resistor connected between the RT pin and GND.
- What is the purpose of the skip cycle mode in the LM5021MM-2?
The skip cycle mode reduces power consumption at light loads, increasing efficiency in energy-conserving applications.
- How does the LM5021MM-2 protect against overcurrent conditions?
The LM5021MM-2 features cycle-by-cycle overcurrent protection and enters a hiccup mode during sustained overcurrent conditions to reduce component stresses.
- What is the operating temperature range of the LM5021MM-2?
The operating temperature range is -40°C to 125°C.
- What is the startup current of the LM5021MM-2?
The startup current is 25 µA maximum.
- Can the LM5021MM-2 be synchronized to an external clock source?
Yes, the oscillator can be synchronized to an external clock source by capacitively coupling a pulse train into the RT pin.
- What is the gate driver current capability of the LM5021MM-2?
The gate driver can source 0.3 A and sink 0.7 A.
- How does the soft-start feature work in the LM5021MM-2?
The soft-start feature allows the power converter to gradually reach the initial steady state operating point by charging an external capacitor connected to the SS pin, reducing start-up stresses and current surges.
- Is the LM5021MM-2 compliant with EU RoHS regulations?
No, the LM5021MM-2 is not compliant with the latest EU RoHS regulations as it has been discontinued.
