Dynamic Envelope Tracking in a power supply for the automotive market
The Problem to be solved: 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.
The Intersil solution: The ISL78227 and the ISL78229 (with PMBus). These two 55V two-phase synchronous boost controllers with integrated high-side and low-side MOSFET drivers are a robust solution with the unique use of Dynamic Envelope Tracking (Intersil claims to be the first in the industry and I have not seen anything else like this). More on this later.
Operating from a 12V battery supply, these devices boost the 12V battery supply to output voltages of 24V, 36V or 48V for premium 200W to 800W trunk [boot] 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% efficiency to reduce 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 bill of materials 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 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 1 MHz, 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 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% to 65%. The feature of adjustable minimum on-time enables a low boost duty-cycle which is able to increase the low end track range. See Figure 1.
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.
The automotive audio power amplifier
An example showing how Dynamic Envelope Tracking benefits the audio power amplifier in an automobile is whenever the battery supply is low, power consumption of various components such as the audio amplifier must be limited, especially if the radio is on while the engine is off. Transient events such as the start-stop system restarting the engine also require on-the-fly voltage adjustments.
The audio amp will not have any glitches or pops with Envelope Tracking used in the power supply. See Figure 2.
Figure 2. Advantages of Dynamic Envelope Tracking in Automotive Audio Power Amplifiers (Image courtesy of Intersil)
Peak current mode control
The advantages of Peak current mode control are simpler compensation needed, better load transient response, and fast line transient response from the 12V typically moving up and down during operation.
12V to 48V boost in automotive applications
This boost is needed for such applications as a motor-driven electrically adaptive suspension system which can dynamically adjust while driving. Also, the adaptive energy coming from shock absorbers to charge Lithium Ion batteries is another example of the 12V to 48V boost need.
Reliability, safety and circuit protection
These ICs have extensive protection built in by Intersil designers to keep them operating under all the harsh conditions experienced in an automotive environment. See Figure 3.
Figure 3 The ISL78227 and ISL78229 are protected with a robust internal design. (click to expand) (from ISL78229 data sheet).
In order to simplify the task of attaining the ISO 26262 automotive safety integrity level (ASIL) rating, the ISL78229 version has a digital PMBus interface for advanced control, telemetry and diagnostics. Having the PMBus interface on-chip eliminates the need for dedicated telemetry circuitry required to configure fault types, system recovery and monitoring.
Watch this video about the ISL78227/29 solution.
PowerNavigator GUI simplifies digital power designs
Intersil’s PowerNavigator software sets up the ISL78229’s PMBus configuration, validation, monitoring, and telemetry. The tool makes it easy for designers to change features and functions of a digital power supply design without writing code. A download of the PowerNavigator GUI and a tutorial video are here.
The ISL78227 and ISL78229 can be combined with the ISL78206 40V/2.5A synchronous buck controller, ISL78310 1A LDO, and ISL78233 3A synchronous buck regulator to provide a complete power solution for an automotive audio amplifier power supply. The ISL78227 55V synchronous boost controller comes in a 5 × 5 mm, 32-lead WFQFN package and the ISL78229 55V synchronous boost controller with PMBus in a 6 × 6mm, 40-lead WFQFN package; evaluation boards (see below) are available.
Intersil; www.intersil.com
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