USB Power Delivery on Battery Operated Devices [Group 1]June 19, 2013
- Battery operated and complex devices, like smartphones, tablets, portable PCs, cameras
- USB peripherals, like external hard disks, printers or usb
- No-USB peripherals with <100W power consumption like monitors, toys and gadgets
- Power supply devices like wall chargers, power bricks.
Each category has different needs, requirements and constraints and it’s logic to foreseen for the USB-PD different possible implementations and implications in the system architecture.
Let’s start with the 1st category, the most complex.
Battery Operated Devices
This category includes all the devices with a battery as primary power source and with a USB port used for secondary energy source for battery recharge. This is clearly the most complex device, as it can play as an energy consumer (during internal battery recharge) or as an energy provider (in case, for example, of supplying an external hard disk). I’m clearly referring to Tablets, smartphones and portable PCs. They have already complex power policies and strategies and one or more USB ports for data communication. So not a big issue to integrate a USB-PD feature in such devices. Quite easy from a mechanical point of view, but it’s worth to discuss deeper the possible electronic implementations.
Such devices have normally complex and dedicated power management unit (PMU or PMIC) that implements complex power management functions, energy saving algorithms and battery charge strategies in collaboration with the CPU to extend as much as possible the battery life. Without trying to be exhaustive and with different level of integration, some examples of such ICs can be the TPS65950 in the picture from TI and the DA9034 from Dialog.
The technology trend is moving toward the integration in a single IC of most of the mixed-signal functions available in a portable device (audio power amplifiers, mic amplifier, backlight driver, HDMI and other I/F physical interfaces), including a USB PHY/controller interface.
In case of PMU/PMIC, it is easy for me to image the integration of the USB-PD in this IC, at least the PHY, letting
the cpu to manage the upper layers (from Protocol Layer and up) and the negotiation policy of the USB-PD standard.
This approach should be the preferred solution in case of high volume, high level integration and BOM and assembly cost reduction. Major semiconductor players in the PMU/PMIC domain and Silicon IP vendors will work to integrate this new feature and to deliver soon USB-PD PHY solutions for integration.
In case of devices with a simpler PMU, a possible implementation of the USB-PD can be done using a standalone IC implementing the PHY and/or the upper layer.
This IC should be anyhow interfaced with the main CPU for upper layer protocol implementation. This “discrete” implementation will depend on the availability of a standard IC component from the major semiconductor companies.