TI Home > News Releases

News Releases


Targeted For Motherboards and Add-in Cards, the LMC6953 Protects Both 5V and 3.3V Power Supplies From Potentially Catastrophic Fault Conditions

Nov 25, 1996

November 25, 1996 -- National Semiconductor Corporation® today announced a voltage supervisory chip designed, tested and guaranteed to meet revision 2.1 of the PCI (Peripheral Component Interconnect) specifications. The LMC6953 monitors both 3.3V and 5V supplies during power-up, power-down, brownout, power failure and manual reset interrupt. It then generates a reset output if either supply fluctuates from the designated PCI specifications. The device also monitors the two supplies with respect to each other and, should polarities reverse, generates reset with a faster response in order to prevent catastrophic failure of any component on the bus. The LMC6953 is suitable for servers, desktop PCs, PCI add-in cards and embedded PCI systems such as test equipment and communication servers.

"The real estate and economic cost of a PCI-compliant reset circuit has, until today, been a problem for our OEM customers," according to Mark Downing, National's marketing director/input signal management products. "The need for high reliability often compels designers to protect PCI-based systems with circuits having as many as 30 components, despite the board space and cost impact. Now, the LMC6953 gives them another option, one that lowers cost and meets PCI requirements without sacrificing board space,"he said.

Other key features include an accurate built-in bandgap reference that accurately determines all threshold voltages. Reset response time is 490 nsec max for brownout conditions and 90 nsec for power failure. In accordance with PCI specifications, a precise reset delay timing of 100 msec occurs after both 5V and 3.3V powers recover, or after manual reset signal returns to high state. Using the LMC6953's open-drain outputs, designers can connect an external resistor so that the output can be used as a level shifter for mixed voltage systems up to 6V.

About PCI
PCI Bus is rapidly becoming the standard interface for add-in-cards used in high-end desktop PCs and servers. Designed to operate at 3.3V, 5V or both, the PCI Bus offers higher data throughput and improved connectivity to existing ISA- and EISA-based systems. Because of higher data rates, any power fluctuations on the bus, such as brownout, can have a catastrophic impact on the integrity of the data being transferred. Brownout occurs when a 5V supply is above 5.75V or below 4.25V. It also occurs when a 3.3V supply is above 4.1V or below 2.5V. The PCI specification addresses this problem by requiring the bus to reset itself when the voltage supplies fall out of tolerance.

National Semiconductor produces analog and mixed-signal based silicon solutions for the information highway, communications, consumer and industrial markets. National Semiconductor is headquartered in Santa Clara, California, and has 19,000 employees worldwide. In fiscal 1996, the company reported sales of $2.6 billion.