Hirotada Honma, Application Engineer, ON Semiconductor
As modern life increasingly depends on being always connected – to work colleagues, social contacts, family, smart home appliances – people’s desires for seamless connectivity are driving changes in car infotainment systems. Demand for new and better in-car equipment that suits today’s digital lifestyles, looks good, and avoids driver distraction should power the market for infotainment systems above $35 billion by 2020, according to analysts.
From a design perspective, infotainment equipment is becoming increasingly complex. The days of the simple DIN-size radio/CD player are long gone, although these legacy features are still required in a unit that supports many additional functions such as internet connection, smartphone connection, satellite navigation with auxiliary inertial sensing, camera feeds, graphical touchscreen, multi-display output for other passengers, and more.
Complex System-Power Requirements
All this calls for a huge quantity of circuitry behind the dashboard, which has a multitude of engineering implications. Space is severely limited, and although semiconductor integration can mitigate this to some extent, a wider variety of ICs are being used, including high-performance processors or FPGAs/ASICs, interface chips, display controllers, analogue components. As a result, many more power rails are needed, at a variety of voltages from as low as 1.5-3.3V for low-voltage logic devices, 5V, 8V or 9V for the legacy tuner and CD circuitry, and 10-12V for other circuits such as console lighting. In the past, when many fewer supply voltages were required, engineers could ensure adequate power control using an individual regulator for each rail. This approach becomes untenable, as space restrictions have a greater influence over design decisions.
Thus, power management for the emerging generation of highly featured, connected in-vehicle infotainment systems is essential. Simply extending the traditional approach, using an array of discrete voltage regulators to supply each rail, can result in a system containing large number of individual components as shown in figure 1. The passive components needed externally to each regulator add further to solution size and bill of materials costs.
A more integrated approach is required, such as a Power-Management IC (PMIC), but designers need to take care. If the PMIC is designed with the latest infotainment system requirements, the solution may contain features that are not required.. System designers need to choose a PMIC with suitably rated power rails, integrates protection features, and give flexibility for software adjustmentswhere necessary to optimizesystem requirements.
This is the approach ON Semiconductor has taken when designing the LV56851UV multiple-output system power-supply IC for automotive infotainment applications. There are five linear regulators (LDOs) on-chip, as well as a high-side switch. This integrated approach also simplifies provision of the necessary protection mechanisms, including power-supply over-voltage and over-current protection, as well as thermal protection that effectively prevents damage by generating a warning if the IC temperature exceeds 140°C and initiating thermal shutdown above 175°C.
In addition, integrated functions such as battery-voltage detection and monitoring of the accessory (ACC) power-supply voltage save additional external components. An external amplifier supply (AMP) is provided, further aiding overall component savings, and the IC also provides a forced-reset capability that helps designers meet international safety requirements for automotive electrical systems. Figure 2 illustrates the LV56851UV features in relation to infotainment system power requirements, which contrasts with the design based on discrete components as shown in Figure 1.
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Figure 2. Integrated multi-output power-supply IC optimized to meet infotainment-system demands.
The five LDOs are designed to supply logic devices and processors operating from 3.3-5.5 V and 1.25-5 V, as well as audio/tuner and CD circuitry, and an illumination supply at 10-12 V. The integrated high-side switch can be used to help manage a USB port for connecting devices such as smartphones or personal media players inside the vehicle.
An important feature of this device is I2C programmability of the system, audio, CD and illumination outputs. This not only allows individual rails to be turned on or disabled as needed, but also allows adjustment of the output voltages. This gives designers flexibility to satisfy individual system requirements, or to quickly implement any design changes without needing to change external components. The high-side switch output can also be enabled or disabled using I2C commands.
Putting more On-Chip
Additional features that help save PCB real-estate and reduce bill of materials costs include the battery-voltage detection, which eliminates the need for a conventional Zener-based detection circuit that typically comprises three transistors, two diodes, two capacitors and four resistors. Figure 3a and 3b compare a typical discrete circuit with the integrated detection circuitry on-board the LV56851UV. Detection accuracy is also improved to ±3%, whereas a conventional circuit cannot be accurate to better than ±5% owing to the typical tolerance of a Zener diode. In addition, the under- and over-voltage detection thresholds for a discrete solution are typically highly temperature dependent. In contrast, the integrated detector circuit has very stable temperature characteristics.
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Figure 3a and 3b. Integrated battery-voltage detection circuitry saves component count and PCB area.
The ACC under-voltage detection also provided in the LV56851UV enables to send under-voltage detection signal to the MCU. Eight discrete components, including a Zener diode, transistor and capacitor, as well as five resistors, are saved by integrating this circuitry on-chip. Built-in reset circuitry also enhances temperature stability and detection accuracy. The I2C-bus connection provides a channel for reporting the battery voltage and ACC voltage, as well as other diagnostic information, to the main system controller.
The compact HZIP15 package provides improved functionality within a 15-pin form factor. While the output current ratings of the regulator outputs are tailored to supply the needs of connected circuitry – such as the 1500 mA output rating of the DC output, which can be set between 5 V and 8 V by I2C commands – the IC has very low quiescent current and draws only 60 µA in standby.
Using an integrated system power-supply IC, instead of a discrete voltage-regulator array or a “best-fit” PMIC that is not ideally suited to the needs of today’s infotainment systems not only helps manage board size, reduce the bill of materials, maximize energy efficiency and protect against thermal threats, but also simplifies design and helps to save weight, thereby minimizing the infotainment system’s impact on vehicle fuel economy.
The future of automotive infotainment is moving toward more sophisticated systems conceived to deliver superior experiences for drivers and passengers. Greater convenience and connectivity demands extra functionality, but it is essential to keep the component count and circuitry to a minimum. Greater semiconductor integration offers a way forward, including integration of the power-management subsystem. The emerging generation of multi-output system power-supply ICs enable a space- and energy-efficient solution.