As multiple voltages proliferate across a single pc board comprising processors, application-specific ICs (ASICs), field-programmable gate arrays (FPGAs), as well as analog and power circuits, they are stimulating demand for supervisory and power management chips. These devices can perform margining, monitoring, tracking and sequencing of multiple supply voltages. These actions ensure proper functioning of the myriad devices found on today's complex circuit boards.
“It's common today to have a DSP or a CPU operating at 1.5 V, memory at 1.8 V, and traditional components at 3.3 V or 5 V,” notes George Paparrizos, product marketing manager at Microchip Technology Inc. (Chandler, Ariz.). “Also, in the interest of greater system efficiency, DSPs and CPUs today may have an I/O voltage that's different from their core voltage.”
Shyam Chandra, analog marketing manager at Lattice Semiconductor Corp. (Hillsboro, Ore.), adds, “Most system-level integrated circuits, whether processors, ASSPs, ASICs or FPGAs, have device-specific power supply sequencing and tracking requirements that make each printed circuit board power-supply management design unique. Traditional approaches, consisting of arcane collections of resistors, capacitors, discrete analog and logic functions, are no longer practical solutions.”
Microchip and Lattice are taking different paths to a power management solution. Microchip offers several single-reset ICs, but it has yet to introduce a device specifically for multiple reset or power sequencing applications. “Customers who need those capabilities use our microcontrollers,” he says. “For a customer that can do firmware development, it's a pretty straightforward solution that provides almost unlimited flexibility.” Customers are likely to opt for a microcontroller solution if the need for flexibility outweighs the need to conserve board space.
Devices in Lattice's ispPAC family of mixed-signal programmable logic devices (PLDs) combine programmable logic with voltage comparators, references and high-voltage FET drivers. The ispPAC-POWR1208, for example, features 12 precision analog threshold comparators with on-chip voltage references for supply monitoring; four noise-immune digital inputs and four open-drain digital outputs for system control interfacing; four high-voltage FET drivers, programmable for maximum voltage and ramp rate, for supply control, and four programmable timers with an on-chip 250-kHz oscillator for delay control.
Improper power-supply sequencing can cause potentially disastrous latch-up problems. The SMT4004A from Summit Microelectronics (San Jose, Calif.) is designed to prevent latch-up in processor, ASIC and FPGA multi-rail components. Operating from power supply voltages as low as 2.7 V, it can be configured to track up to four power supplies differentially as they follow an internally generated 100, 250, 500 or 1000 V/s ramp during power-up or power-down. It can control supplies as low as 0.9 V. Four independent resets, two interrupts, a forced shutdown circuit-breaker function and crowbar shutdown functions are customer programmable.
The PS-1648 (self-powered from 48 V) and the PS-1624 (24 V), developed by Potentia Semiconductor Corp. (Ottawa, Ontario), provide power management for up to six dc-dc converters or nonisolated voltage regulator modules. In addition to controlling start-up/shutdown sequencing, the devices take charge of monitoring, trimming and fault handling. They can control dc-dc converters with primary- or secondary-side on/off inputs without the need for external components. Each device monitors the input voltage to ensure reliable start-up and flag undervoltage faults.
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