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2.1 Power Topologies for Automotive Cold-Crank Conditions
Let's say you go out to start your car on a very cold winter day. The extreme cold increases the amount of energy required to turn on your vehicle's engine and reduces the amount of current year battery can provide. Due to the combination of these factors, the vehicle experiences a cold-crank condition when started, meaning the battery voltage can drop as low as three volts. Now, let's take a look at some power tree topologies that can operate through cold-crank conditions. First, let's look at the pre-boost topology. The pre-boost power tree topology is a multi-stage power tree that implements a wide input voltage boost converter controller, followed by a second stage wide input voltage bucks, or LDOs. The boost converter only operates when the battery voltage drops below a specific threshold. When the battery voltage drops, the boost will create an intermediate voltage that allows the downstream power supplies to continue operating. Next up is the buck boost power tree topology. With a buck boost power tree, a wide input voltage buck boost converter controller provides the first stage voltage rail, followed by additional low-input voltage bucks, or LDOs, depending on the number of voltage rails needed. Due to the buck boost's ability to both step up and step down in input voltage, the system can operate through cold-crank start-stop conditions, as well as provide one of the system's main voltage rails. Finally, we come to the pre-buck power tree topology. Although there are multiple versions of the pre=buck topology, only the buck boost topology can potentially operate through cold-crank conditions, depending on the OEM cold-crank specification. The buck to boost topology is a first stage wide input voltage buck followed by a second stage low input voltage boost, and additionally, bucks and LDOs if needed. The first stage buck will typically provided a voltage such as 3.3 volts, allowing the buck to operate in an input voltages around 3.6 volts. Therefore, if the OEM spec for cold crank is not as severe, the buck to boost power tree topology can operate through such conditions. For more information on power tree topologies and their benefits and tradeoffs, please read the BC Empower Topologies white paper.
Watch the previous video in the series:
Power Topologies for Automotive Start/Stop Conditions
Details
Date:
November 9, 2018
In this video, learn about how cold-crank functions of a vehicle impact the power supply during harsh operating conditions.
Additional information
Read about how the power-management architecture varies with the complexity of the BCM in this white paper
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