Consumer products, especially hand-held devices, are becoming increasingly complex as many different electrical and electro-mechanical devices with a myriad of voltage levels and current requirements are powered off a single cell battery or a wall supply when the battery is recharging. The supply in these products has to convert this single voltage level to power multi-voltage Processors, DSPs and ASICs, SDRAM, memory sticks, flash memory, focus and zoom lens motors, audio and LCD screens with white LED backlighting. Furthermore, device voltage levels for multi-voltage Processors, DSPs and FPGAs are down to 1.2V and are approaching 0.9V, making system tolerances tighter and necessitating a precise way to keep these voltage levels within specifications. At the other extreme, stacked white LED backlights require as much as 30V with precise current control to power up to10 white LEDs in series. To further complicate matters, all these devices need to be turned on/off at different times for both reliability reasons and to conserve battery life. If all these requirements are not followed, performance degradation, fault conditions such as bus contention, poor battery life due to current spikes during start up or device latch-up can arise.
This article describes a power management method for handheld equipment suppliers to achieve high system reliability while still meeting power density requirements of small-footprint portable devices as well as meeting low cost targets and low power. New digitally programmable power supplies provide I2C programmable output voltages, individual supply enable control, battery monitoring, UV and OV monitoring on PWM outputs, margining/LED backlight level, slew rate control and programmable power on/off sequencing. Actively controlling DC output voltage levels to within ±0.5% under low to high line/load to meet stringent tolerance requirements of high performance components further extends reliable operation. Margining supplies test system performance goals as well as providing an easy way to make adjustments, such as brightness and volume as well as dynamic voltage management for processor core voltages. The integration of active accuracy control, programmable features and built-in flexibility allows the system designer to create a “platform solution” that can be easily modified via software without major hardware changes. Combined with re-programmability, this facilitates rapid design cycles and the proliferation from a base design to future generations of product. Digitally programmable analog power management also allows the digital design engineer to master an otherwise complex system power design with minimal analog knowledge or experience. The use of non-volatile programming also means the power subsystem does not have to be reloaded at every power cycle.
How to standardize a system with no standards
With more complex handheld systems such as Portable Media Players, Digital camcorders/still cameras, Smart PDA/Camera phones, Handheld GPS/PDA’s all with TFT-LCD and now OLED Displays, there is also an increasing power supply complexity with larger numbers and variety of voltages, sometimes as many as 12 unique supplies. Also with the increasing number of supplies, supply ordering becomes critical because of the cumulative input current demands during turn-on and turn-off of all the supplies. Add to that the additional power consumption and associated temperature rise and tighter supply accuracy at lower and lower voltages, makes it increasingly difficult to improve or maintain reliability. All this with demands for shorter development times, less expensive products and improved availability requires a new platform solution for handling all these design issues. Therefore the benefit of standardization of system power management allows the power chain and monitor functions to be the same across several platforms.
To help standardize, a digitally programmable supply platform with an analog controller/Converter provides advantages over fixed solutions as well as pure digital PWM control. One advantage is that a programmable solution reduces risks associated with changing system requirements. With a programmable solution the sequencing order can be modified and sequenced channels can be replaced with tracking channels by simply reprogramming the controller. This minimizes the potential for having to re-spin the board when the system requirements are not clearly understood. A programmable solution also gives the designer more confidence that the board will work the first time. If a problem is encountered, reprogramming can get past the problem and onto debugging and testing the board for its intended function. On a company wide basis, the programmable solution also allows for cross platform implementation where an existing design can be reused for a unique solution by simply reprogramming. The analog PWM and LDO allow a smaller and less complicated device and hence a less expensive solution than having a full DSP on chip. The analog process also allows power MOSFETS to be integrated where it’s feasible and the PWM to operate at different programmable frequencies to reduce external component size. To do this with a DSP requires extremely high clock frequencies, external crystal and associated high-resolution A/D converters to get accuracy. The digital approach also suffers from quantization error issues. A fully programmable power supply with integrated non-volatile (NV) trimmed analog PWM controllers provide all the power management needed in any power system. This programmability allows high performance analog with <0.5% accuracy="" over="" process="" and="" temperature="" using="" a="" standard="" digital="" cmos="" process="" with="" non-volatile="" analog="" trim="" at="" a="" substantially="" lower="" cost.="" flexibility="" through="" nv="" programming/re-programming="" and="" configurable="" hardware="" functions="" with="" programmable="" analog="" parameters="" using="" a="" digital="" interface="" to="" the="" system="" and="" gui="" development="" tools="" makes="" standardization="" easy="" to="" achieve.="" because="" it="" is="" an="" analog="" function,="" high="" integration="" combines="" power="" delivery="" and="" regulation="" with="" the="" programmable="" power="" control.="">0.5%>
Figure 1 –
Typical handheld power management system. Since the power manager is fully configurable, if the system blocks change, so can the manager. There are 8 voltage outputs, consisting of: three synchronous PWM "buck" step-down converters, one configurable PWM “boost or buck” converter, three configurable PWM "boost" step-up or inverting, one Low Dropout (LDO) linear regulator, and a fully programmable 1 or 2-cell Li-Ion battery charger.
Figure 2 –
Non-volatile Programmable Functions. All voltage levels and triggers are programmable using a Windows GUI and a PC-compatible parallel or USB port to I2
C serial bus programmer. Power management design is simplified and when power is removed, all settings are remembered