Cranking simulator made easy

January 27, 2014 // By Matthias Ulmann
Matthias Ulmann outlines how to manage the drop of battery voltage during cranking of an engine.


Electronic engineers working in the automotive area are sooner or later faced with a 'Cranking Test Pulse'. These test pulses describe the drop of the battery voltage during cranking of the engine and all car manufacturers have their own standard for them. Since plenty of electronic circuits are attached to the battery, these are impacted by this event. In some applications like the navigation- or multimedia- system, an interruption of operation due to the drop of the input voltage is not wanted or even acceptable. In this case, mostly a boost convert is placed in front of the circuit to provide a stable input voltage for the electronics.

During the development process the functionality of this pre-booster must be tested to ensure a fast start-up and a clean and stable output voltage for the subsequent electronics like point-of-load converters. A typical solution for this kind of applications is Texas Instruments TPS43330 providing two synchronous buck converters and a boost. The battery voltage is connected directly to the boost and the two bucks are connected to the output of the boost.

As soon as the battery voltage drops below an adjustable threshold, the boost starts up and supplies the bucks with a constant voltage of 7 V, 10 V or 11 V.

Plenty of manufacturer offer test system to simulate cranking pulses, but unfortunately they have also 'commercial' prices. To test automotive electronic systems up to 50 W input power with different standardized cranking pulses, the small and inexpensive cranking simulator shown in the following can be used.


Basically, a flexible programmable, arbitrary signal generator is needed, which covers an output voltage rang of 2 V to 15 V and a maximum output power of 50 W. These requirements can be divided into three areas.

For the power section, a buck converter is the right choice, as no galvanic isolation is needed and it generally achieves the highest regulation

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