Description

The PMP9477 design is a conducted EMI optimized multi-output power supply for automotive cluster units.  The power supply has a pre-boost stage for cold crank and start-stop operation and two buck regulators.  The pre-boost stage features the LM3481 boost controller and will start to operate and regulate a 9.5V output when the input voltage drops below 9.5V.  It makes the design a wide input voltage range of 4.5V to 38V suitable for 12V automotive battery systems.  The design has two buck regulators following the pre-boost to generate 3 output voltages: the first stage buck generates a 5V: 2A output using the LM26003: and the second stage generates two outputs of 2.8V: 2A and 1.8V: 2A using the LM26420 (the max output power is 15W).  The LM26003 is a wide Vin non-synchronous buck regulator: and the LM26420 is a 5V input dual 2A: high frequency synchronous buck regulator.  All three ICs are available in automotive grade versions: qualified in AEC-Q100 Grade 1.  The board layout is optimized for improved conducted EMI performance.  The power inductor in the pre-boost stage is utilized as an input EMI filter: and thus no additional filter components are required.  The board is tested under the automotive EMC standard: CISPR 25: and its conducted emissions are in compliance with the CISPR 25 Class 5 requirements.