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Power supplies boast dynamic envelope tracking for car space

Posted: 02 Mar 2016     Print Version  Bookmark and Share

Keywords:Intersil  dynamic envelope tracking  MOSFET  automotive  PMBus 

Intersil has a couple of things in its arsenal that just might revolutionise how automotive power systems are developed. The company has been looking at how to efficiently and effectively handle any and all available automotive voltages of 24V/36V and 48V (usually more the high end cars) in automotive power systems in a single design. Now, it has released the ISL78227 and the ISL78229 (with PMBus), which are two 55V two-phase synchronous boost controllers with integrated high-side and low-side MOSFET drivers that demonstrate unique use of dynamic envelope tracking.

Operating from a 12V battery supply, these devices boost the 12V battery supply to output voltages to 24V, 36V or 48V for premium 200W to 800W trunk audio amplifiers, start-stop systems and headlamp LED strings.

These devices enable a modular design for systems requiring power and thermal scalability. They support wide input and output ranges of 5V to 55V and deliver greater than 95 per cent efficiency to lower power loss and improve upon heat dissipation. The architecture interleaves two controllers for a four-phase application which in turn doubles the output power and reduces input/output ripple. This will enable designers to use smaller capacitors to save board space and lower their BOM cost.

Since the automotive environment is a harsh one, there are numerous protection features to keep the ICs operating under just about any condition. Intersil designers have implemented a unique soft-on function which ensures smooth transition from discontinuous-conduction mode (DCM) to continuous-conduction mode (CCM) after completing a soft-start. This keeps the power supply safe under all start-up conditions. The CCM operates at 1MHz, single phase which is above the AM radio band and will not interfere with reception.

Envelope tracking

I am very familiar with the technique of envelope tracking in base station and handset power amplifiers. The Intersil designers cleverly realised that by tracking the input and changing the output accordingly, they were able to optimise or dynamically limit the output power to meet all automotive system load requirements. The designers were very familiar with dynamic envelope tracking from their audio amplifier power designs and now saw the benefit in the overall automobile power system. This envelope tracking function can use an analogue signal from 0.3V to 1.6V or alternatively a PWM signal of 20 per cent to 65 per cent. The feature of adjustable minimum on-time enables a low boost duty-cycle which is able to increase the low end track range.

Track function

Figure 1: The track function can utilise an analogue or a digital track signal. (Image courtesy of Intersil)

So the envelope-tracking feature will dynamically adjust or scale the output voltage on the fly to meet all system load demands. Heating the automobile windshield is another very good dynamic envelope tracking application.

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