Single-Ended Primary Inductor Converter (SEPIC) Automotive LED Driver Reference Design
Created: Sep 03, 2014
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The microchip's automotive LED driver reference design focuses mainly on switching and DC-DC conversion. Through modifying the board components' values, the output current can be obtained. The board has a 350mA or a 700mA constant current source with some modification on the hardware. The main component of this particular reference design is a MCP1630 8-pin microcontroller. This design is found on typical automotive applications that sustains high-voltage peaks.
The MCP1630 device provides all the analog functions necessary to implement a peak current mode PWM DC-DC converter. The powertrain is based on the Single-Ended Primary Inductor Converter (SEPIC) topology. This topology offers the buck-boost functionality and also has a non-pulsating input current. The converter provides an adjustable constant current at the output, necessary to drive high-power LED applications. The MCP1630 PWM controller requires an external clock for operation. This clock is provided by an external 8-bit microcontroller, PIC12F683. The PWM frequency and the maximum duty cycle are set by this clock. The output (load) current is sensed with a 0.5Ω shunt resistor (R17 and R18). The voltage across this shunt resistor is compared with the reference voltage by the MCP1630 device's PWM controller. The reference voltage for the MCP1630 device is also provided by PIC12F683, at the VREF pin (Pin 8). R4, R3 and C2 form a low-pass filter that smoothen the PWM signal produced by the PIC microcontroller. The maximum output current is set by the R4 and R3 voltage dividers. The duty cycle of the PWM signal is adjusted in eight steps.
The MCP1630 device is used for peak current mode control in a SEPIC power train circuit that can be useful in applications in which a battery voltage can be above and below that of the regulator's intended output. Such instance is a single lithium ion battery that typically discharges from 4.2 volts to 3 volts; if other components require 3.3 volts, and then the SEPIC would be effective.