Infineon BCR198S Low-Dropout Linear LED Driver: Datasheet, Application Circuit, and Design Considerations
The Infineon BCR198S is a monolithic, low-voltage, low-dropout linear constant current source designed for driving LEDs. It provides a simple, cost-effective, and highly reliable solution for applications requiring stable illumination without the complexity of switch-mode power supplies (SMPS). This article explores its key specifications, a typical application circuit, and critical design considerations.
Datasheet Overview and Key Specifications
The BCR198S is engineered to deliver a constant output current with a very low dropout voltage, making it exceptionally efficient for battery-powered or low-voltage systems. Key parameters from the datasheet include:
Output Current: A fixed nominal current of 20 mA, which is the standard for many indicator and general-purpose LEDs.
Dropout Voltage: Extremely low, typically < 150 mV at 20 mA. This allows the IC to continue regulating current even when the input voltage is only marginally higher than the LED forward voltage (Vf), maximizing usable supply voltage range.
Supply Voltage Range: Operates from 3 V to 42 V, offering great flexibility for 12V/24V automotive, industrial, and consumer applications.
Current Regulation: Excellent immunity to supply voltage variations and temperature changes, ensuring consistent LED brightness.
Package: Offered in a compact, surface-mount SOT-143 package, saving valuable PCB space.
Typical Application Circuit
The implementation of the BCR198S is remarkably straightforward, a significant advantage over switching regulators. The basic application circuit requires only a single external resistor.
1. Circuit Configuration: The LED anode is connected to the positive supply rail (VCC). The cathode is connected to the OUT pin of the BCR198S. The GND pin is connected to the system ground.
2. Setting the Current: The constant output current is primarily set by a single external resistor (REXT) connected between the REXT pin and ground. The datasheet provides a formula and a graph to select the precise resistor value for the desired current. For the standard 20 mA, a specific value (e.g., 18 Ω) is recommended.
3. Operation: The internal circuitry of the BCR198S automatically adjusts its impedance to maintain a constant current through the LED, regardless of fluctuations in VCC or the LED's forward voltage.
Critical Design Considerations
While simple to use, several factors must be considered for a robust design:
Power Dissipation and Thermal Management: This is the most crucial consideration for linear regulators. The power dissipated by the IC is calculated as PD = (VCC - VLED) IOUT. At higher input voltages or current levels, this dissipation can be significant.
Solution: Ensure the operating point does not exceed the maximum junction temperature (150°C). Use the thermal resistance (RthJA) from the datasheet to calculate the temperature rise. For high VIN - VLED differentials, consider increasing copper area on the PCB connected to the GND pin for heatsinking.
Input Voltage Transients: In automotive environments, load dump and other transients can exceed the 42V absolute maximum rating.
Solution: Implement protective circuitry, such as a transient voltage suppressor (TVS) diode or a simple Zener diode at the input, to clamp any voltage spikes and protect the BCR198S.
Parallel and Series Operation: For driving multiple LEDs:
Series Connection: A single BCR198S can drive a string of series-connected LEDs. Ensure VCC is greater than the sum of all Vfs plus the dropout voltage.
Parallel Connection: Avoid directly paralleling multiple BCR198S outputs to drive a single high-current LED due to potential current sharing imbalances. Instead, use one driver per LED string for independent and reliable current control.
Dimming: While not a dedicated dimming controller, the BCR198S can be dimmed using Pulse-Width Modulation (PWM). By applying a PWM signal to the VCC input (or using a switch between OUT and the LED), the average current through the LED can be effectively controlled without shifting color coordinates.
The Infineon BCR198S stands out as an exemplary solution for simple, efficient, and robust LED driving. Its ultra-low dropout voltage extends battery life and operational range in low-voltage systems, while its minimal external component count reduces design complexity and BOM cost. It is an ideal choice for applications where noise-sensitive switching regulators are undesirable and operational simplicity is paramount.
Keywords: Low-Dropout (LDO) LED Driver, Constant Current Source, BCR198S Infineon, Automotive LED Driving, Thermal Management
