powerZONE Products for the week of October 15, 2001
Linear Technology Says . . .
LTC1644: Hot Swap Controller Protects CompactPCI Systems
and Supports System Requirements During Live Insertion
Linear Technology introduced the LTC1644 CompactPCI Hot Swap controller
that controls all four supply voltages as well as pre-charging the data
bus pins and generating the local reset signal. Internal switches control
the ±12V supplies while external N-channel transistors control the
3.3V and 5V supplies. Circuit breakers on all supplies feature foldback
current limiting allowing over-current transients to be limited without
latching off. Short-circuit faults cause the circuit breakers to latch off
after a programmed time. Controlled ramping of the supplies limits inrush
current and a 1V precharge bias voltage is available to limit disturbances
on the data bus pins. The system reset signal is logically combined with
the healthy signal to create a local reset signal. These features allow
CompactPCI cards to manage the power supplies during hot swapping and protect
the card from over-current faults.
The LTC1644 integrates supply supervisory features to properly interface
to the power management logic. Voltage monitors on all supplies provide
the HEALTHY# signal to indicate that the supplies are within regulation.
These monitors, in combination with the PCI_RST# signal, in turn generate
the LOCAL_PCI_RST# signal for the local processor. If necessary, a FAULT#
output can be used to indicate that the circuit breaker has tripped.
analogZONE Says . . .
There is no way that you could describe LTC's family of hot swap controllers as "simple" but they are extremely elegant solutions based on the same continuing, logical approach. This latest product, the LTC1644, hits a major market sweet spot for allowing safe board insertion and removal in CompactPCI (CPCI) bus use and will be a volume product for the company.
The part allows for protection of all four supplies normal to CPCI of 3.3 V, 5.0 V, +12 V, and -12 V but if they are not all being deployed the part can still be used provided the +12 V rail is available -- as this is what drives the IC itself. The -12 V input can be tied instead to ground and either the 3.3 V or 5.0 V rail can be missing. The supply current is a typical 4 mA. The foldback current limits are programmable with a value depending on output voltage; if any of the supplies remains in current limit too long then the respective circuit breaker will trip; in the event that either the 5.0 or 3.3 V supplies exceeds the nominal current limit by three times then all the supplies are turned off, asserting the fault logic. The supplies are allowed to power up in current limit, allowing widely different capacitive loads to be handled; during power up the supplies must remain out of current limit, otherwise all the pass transistors will turn off.
As has been the case for this family of controllers, the data sheet is complete without being longwinded, allowing for straightforward implementation.
The LTC1644 is in production in an SSOP-20 and is priced at $3.65 in
1000-piece lots.