powerZONE Products for the week of March 10, 2003
Intersil Says . . .
ISL6561: VRM10 Multiphase PWM Controller With MOSFET
and DcR Current Sensing
CPU voltage regulator provides 2 to 4 phases, 1-MHz switching,
0.5% system accuracy, 6-bit Dynamic VID, 6 X 6 mm QFN
Intersil Corporation, a world leader in the design and manufacture of high performance analog and wireless networking solutions, today announced the new Endura ISL6561 precision 2- to 4-phase PWM controller IC for new VRM10-based platforms. The ISL6561 IC is the world's first PWM controller to offer designers a choice of either lower MOSFET RDS(ON) or output inductor DCR (DC Resistance) current-sensing topologies. This advanced controller is supplied in the space-saving and thermally efficient 40-pad 6 X 6 mm Quad Flat No-lead (QFN) package. It is targeted for new VRM10 desktop, workstation, and server designs where reliability, and precision performance are critical.
"Combined with our QFN packaged MOSFET drivers, the ISL6561 precision controller provides VRM10 platform designers with everything they need to meet stringent performance, space and cost requirements," said Cindy Drapcho, director of Intersil's Desktop Power Products. "The ISL6561 meets all VRM10 specifications and gives designers the freedom of choice for either of the popular current-sensing techniques."
Today's microprocessors require a tightly regulated output voltage position versus load current (droop). This CPU core voltage pre-positioning enables the DC/DC converter to maintain its regulation during severe load transients without the addition of energy-storing output capacitors. The ISL6561 senses the output current by utilizing patented techniques to measure the voltage across the RDS(ON) of the lower MOSFETs or DCR of the output inductor during their conduction intervals. Current sensing provides the needed signals for precision droop, channel-current balancing and over current protection.
The accuracy of the RDS(ON) current-sensing method is enhanced by the
ISL6561's integrated temperature compensation function. Droop accuracy,
phase current balance and over-current protection can be affected by temperature
related changes in RDS(ON) or DCR. The ISL6561 uses an internal temperature-sensing
element to provide programmable temperature compensation. This eliminates
the need for an external thermistor. Correctly applied, temperature compensation
can completely nullify the effect of RDS(ON) or inductor DCR temperature
sensitivity.
analogZONE Says . . .
It seems like each vendor is approaching the problems of powering PC processors in slightly different ways and with different packaging approaches as well. I like this QFN implementation providing not only 2-, 3-, or 4-phase operation but with operating frequencies beyond 1 MHz (giving 4-MHz ripple in 4-phase applications) and a choice of current-sensing solutions with either Rds(on) or dcR.
What is also nice is that there is programmable temperature compensation for Rds(on) changes with temperature that should completely correct the loop. This is provided with an on-chip PTC, although an external NTC can be used in the feedback loop.
No other active components are required with this Intersil solution, just a few resistors and capacitors, and the complete channel current sense system with current balancing is on board. An internal shunt regulator for either 5-V or 12-V biasing is also provided.
A unity gain differential amplifier is on-chip for remote voltage sensing with any potential difference between remote and local grounds being eliminated by the stage, improving protection and regulation accuracy. Because of its main target market, the part uses 5-bit VID codes to change the output voltage from 0.8375 V to 1.600 V in 12.5-mV steps. The part could also be used, of course, in any other high-current application where accuracy and stability are required.
System accuracy is within 0.5% over all variables and for life and there is threshold sensing for synchronizing POR sequencing. Over-current and over-voltage protection are also provided.
This solution should stand Intersil in good stead in the battle for dc-dc sockets in PCs and general converter applications.
The ISL6561 is in production in a QFN-40 and is priced at $1.75 in 1000-piece lots. Reference designs using Intersil's MOSFET drivers are available as are evaluation systems.