In today's convergence world, the complexity of the system demands a lot from the supply and management of power. The world of a single high-power lossy regulator for supplying power to the whole system is long gone by. A typical portable system has a multiplicity of regulators " both in type and in numbers. As System-on-Chips (SoC) provide more to the system in terms of the level of integration, performance and battery-life to the system, integration of power-management into the SoC becomes a natural "low-hanging fruit" to offer to the system-integrators of today.
First, let us take a quick look at what actually necessitates such complex power-regulator requirements. For this, it would be instructive to explore the insides of a cell-phone or any other portable gadget. The following figure shows the functions that a high-end portable gadget would integrate.
Figure 1: Integrated functions integrated on high-end portable device
We will now see how the power-design for such a complex system can be a significant challenge for the system integrator
The system integrator's challenges
Such a complex system requires the system integrator to carefully architect and tailor the power requirements to the individual chips and sub-units. The various aspects that a system integrator needs to consider and balance out are truly many.
For instance, the power-sequencing across chips is an issue that requires investigating often undocumented behavior of the chips and modules being integrated. As if this were not enough, the system integrator needs to understand the power-supply requirements for each chip that's being integrated.
Take for instance an "add-on" communication function on a mobile handheld such as a Bluetooth, UWB, WiMax or a WiFi chip " the system integrator needs to identify the power requirements and their interactions for a list of sub-functions that might go like this:
|| Example requirements on power
| SoC power island-1
||1.2V programmable down to 1.0V at 100mA
| SoC power island-2
||1.0V at 50mA fixed
|| A fixed 1.2V at 10mA, low-noise
| SoC IO power
|| Fixed 3.3V supply
| Analog Front End power
||1.2V fixed low-noise power
||2.5V fixed voltage at very low noise
|| Direct connect to the battery
Table 1: Communications power requirements for hand-held devices