Automotive boost controller paired with step-down DC-DC converter

October 30, 2013 // By Michael Dunn, EDN
Automotive grade power management ICs; non-synchronous boost controller with automatic wake up and shutdown functions supplies a minimum output voltage during start-stop conditions in order to counteract any sag in the vehicle’s battery voltage.

Introducing ON Semiconductor’s latest power management IC for automotive designs, the company's automotive strategy manager Lance Williams notes that the automotive sector has grown in importance for the company, from 9% of its business when it was spun out of Motorola, to 28% today. A main area of focus is in power, with both ICs and power modules; application spaces receiving attention are in the power train, body electronics, safety and, especially, lighting. Williams notes the trend to ever-more LED lighting inlcuding the main front light cluster, with LED headlights that will use switched LEDs for both non-steerable and steerable designs – ON already supplies stepper motor drivers for steerable designs. “We have a complete portfolio of automotive semiconductor parts, with the exception of microcontrollers,” Williams claims. One of the variables he notes is that car makers, “don't [yet] know how many LEDs there will be [in these new cluster designs]”, leaving the semiconductor suppliers to provide a flexible driving capability.

The particular parts that Williams was introducing are two AEC-Qualified ICs with wide input voltage range and extensive operational temperature range, optimised for automotive powertrain and in-cabin deployment.

Running off a 2V to 44V input voltage, the NCV8876 is enabled when the supply voltage drops below 7.2V, then boost operation is initiated once this voltage goes under 6.8V, with the IC driving an external N-channel MOSFET. A quiescent current of 11 µA is drawn when the device is in sleep mode so that power consumption is minimised. Among the protection features are cycle-by-cycle current limiting, thermal shutdown (with a 170⁰C threshold) and hiccup-mode over-current protection. Its peak current mode control with internal slope compensation ensures device stability over the entire voltage range. This also ensures that it is protected during a current fault condition by turning off the power switch for the remainder of the cycle if the current limit is exceeded.

The NCV896530, 2.1 MHz switching frequency, dual