Overview
The LM3401MMX/NOPB from Texas Instruments is a hysteretic PFET controller designed to provide a constant current source for driving high power LED strings. This controller uses comparator-based voltage mode hysteretic control, which offers a simple and stable design without the need for an internal oscillator. The LM3401 operates by monitoring the peak and valley voltage at the SNS pin to control the LED current within an adjustable hysteresis window. This ensures accurate and efficient LED current regulation.
Key Specifications
| Parameter | Value | Conditions |
|---|---|---|
| Input Operating Range | 4.5V - 35V | |
| Output Current Setting | Programmable using R1 resistor | |
| Switching Frequency | Dependent on input voltage and inductor value | Typically around 25% duty cycle |
| Propagation Delay | 46 ns (typical) | |
| Current Limit Threshold | Adjustable with R3 resistor | |
| Minimum On-Time | 150 ns (typical) | |
| Operating Temperature Range | -40°C to +125°C | |
| Maximum Power Dissipation | Limited by ambient temperature and thermal resistance (151°C/W) |
Key Features
- Hysteretic Control: Uses comparator-based voltage mode hysteretic control for a simple and stable design without an internal oscillator.
- Constant Current Regulation: Regulates LED current within an adjustable hysteresis window by monitoring peak and valley voltage at the SNS pin.
- Programmable Output Current: The LED average current is programmable using a resistor between SNS and GND.
- PWM Dimming Capability: Supports PWM dimming with frequencies up to 10 kHz and duty cycles between 1% and 100%.
- Current Limit Protection: Monitors inductor current and activates current limit protection when the threshold is exceeded.
- High Efficiency: Uses a Schottky diode for low forward voltage to maximize efficiency.
- Wide Operating Range: Operates over a wide input voltage range of 4.5V to 35V.
Applications
- High Power LED Lighting: Suitable for driving high power LED strings in various lighting applications.
- Automotive Lighting: Can be used in automotive lighting systems due to its wide operating temperature range and robust design.
- Industrial Lighting: Applicable in industrial lighting solutions where high reliability and efficiency are required.
- Display Backlighting: Used in display backlighting systems where constant current and PWM dimming are necessary.
Q & A
- What is the input operating range of the LM3401MMX/NOPB?
The input operating range is from 4.5V to 35V.
- How is the output current of the LM3401MMX/NOPB set?
The output current is set using a resistor between the SNS and GND pins.
- What is the maximum switching frequency of the LM3401MMX/NOPB?
The maximum switching frequency typically occurs around the input voltage corresponding to a 25% duty cycle and can be calculated based on the inductor value and input voltage.
- Does the LM3401MMX/NOPB support PWM dimming?
- How is current limit protection implemented in the LM3401MMX/NOPB?
Current limit protection is implemented by monitoring the inductor current and activating the current limit when the threshold is exceeded, using a setting resistor connected from the ILIM pin to the VIN node.
- What type of diode is recommended for use with the LM3401MMX/NOPB?
A Schottky diode is recommended due to its low forward voltage, which maximizes efficiency.
- What are the key considerations for selecting the PFET in the LM3401MMX/NOPB circuit?
The PFET should be selected based on the maximum Drain-Source voltage (V_DS), Drain current rating (Id), maximum Gate-Source voltage (V_GS), on-resistance (R_DS(on)), and Gate capacitance.
- How does the LM3401MMX/NOPB handle thermal management?
The maximum power dissipation is limited by ambient temperature and thermal resistance (151°C/W), and proper thermal management is crucial to ensure reliable operation.
- What are the recommendations for layout and grounding in the LM3401MMX/NOPB circuit?
The input capacitor ground should be placed close to the anode of the catch diode, and the SNS and HYS resistors should be placed close to their respective pins and grounded close to the GND pin. An isolated ground area is recommended for the SNS, HYS, and GND pin connections.
- Can the LM3401MMX/NOPB operate at 100% duty cycle?
