Years ago, systems designers had it relatively easy with respect to system power supplies. Logic ran on 5V power; hard and floppy disk drives needed an additional 12V supply; and the rest of the system would operate off of those two supply voltages plus perhaps one more negative voltage supply. The expanded requirements of today’s complex systems demand power subsystems with far more abilities than ever before. In addition to the need for many more supply voltages, more efficient power regulation, power and reset sequencing, and drift insensitivity, today’s complex, low-power system designs need far more precise and programmable control over the supply voltages. The reasons for these additional requirements can be seen in the advanced chips-such as FPGAs, media processors, SOCs, and ASSPs-that lie at the heart of today’s systems. For example, the most advanced FPGAs require three or four supply voltages to help minimize power consumption.
All of today’s complex logic devices (FPGAs, ASICs, SOCs, ASSPs, etc.) have far more complex power requirements. Just one such chip in a system, like the FPGA example above, may need three or four supply voltages. The order and timing in which these multiple supply voltages come up can also be critical to successful system initialization. The order in which these voltages switch off during power-down operations may also be critically important to proper chip shutdown and can also be critical to preventing supply-induced damage to the IC. The timing relationship between a reset line or multiple reset lines and the supply voltages can be quite important as well.
What’s now required is a field-programmable power supply or system (FPPS) that can provide multiple finely programmable supply voltages with independently adjustable ramp-up and ramp-down times and adjustable sequencing delays between the various supply voltages. Such a power subsystem design provides the system designer with the needed design flexibility. The reason such systems are not widely used today is because they have been prohibitively expensive. It’s not that the required foundation technology itself is prohibitively expensive; it’s because power-IC vendors previously had not applied sufficient levels of silicon integration to the design problem. However, that situation was bound to change…and it has.
The newly introduced XRP7704 and XRP 7740 FPPS controller ICs from Exar incorporate all of the functions required to implement a 5-output FPPS. The chips contain four programmable switching voltage controllers with integrated FET drivers that can drive external high- and low-side power MOSFETs to create efficient switching power supplies with current capacities of 5A to 16A per channel for the XRP7704 and XRP7740 respectively. Power MOSFETs and a few additional passive devices are all that’s needed to implement four high-current, switching power sources operating at four different programmable supply voltages. The XRP7704 and XRP7740 also contain a configurable linear, 100mA, low-dropout (LDO) voltage regulator that can supply a fifth system supply voltage (3.3 or 5V). The configurable LDO regulator can be used as a keep-alive power supply for system components that must remain powered up while the rest of the system is powered down.
In addition to the programmable supply voltages, the XRP7704 and XRP7740 can automatically control the power-up and power-down characteristics of the voltage supplies through programmable preset parameters. These FPPS chips can independently control the ramping speed for each of the four voltage channels and they can control the relative timing between the supply voltages. This last characteristic allows the system designer to bring up some supply voltages before others, as required by many complex logic ICs including FPGAs, media processors, ASICs, SOCs, and ASSPs.
The XRP7704 and XRP7740 also incorporate several system-management functions related to the power supply including under-voltage and power-good monitoring, over-temperature operation and fault handling. All of these system monitors are configurable as well and their status can be queried by a host processor via the chip’s I2C interface.
Samples of the XRP7704 are available now and are priced at $4.00 in 1K quantities. Samples of the XRP7740 will be available by the end of October. The XRP7740 is priced at $5.50 in 1K quantities. Additional information can be found at www.exar.com.
(Note: This blog entry is based on a White Paper that I have written for Exar on FPPS controller chips.)
