LTC1644_15 Datasheet, PDF (11/24 Pages) Linear Technology – CompactPCI Bus Hot Swap Controller

TI I G DIAGRA S
t_OC Overcurrent Fault Detect
V_5VSENSE OR
V_3VSENSE
5V OR 3.3V
100mV
FAULT
FALL TIME ≤ 1µs
5V_IN = 5V, 3V_IN = 3.3V
t_OC
1644 TD01
LTC1644
t_SC Short-Circuit Fault Detect
V_5VSENSE OR
V_3VSENSE
5V OR 3.3V
200mV
FAULT
FALL TIME ≤ 10ns
5V_IN = 5V, 3V_IN = 3.3V
t_SC
1644 TD02
APPLICATIO S I FOR ATIO
Hot Circuit Insertion
When a circuit board is inserted into a live CompactPCI
(CPCI) slot, the supply bypass capacitors on the board can
draw huge supply transient currents from the CPCI power
bus as they charge up. The transient currents can cause
glitches on the power bus, causing other boards in the
system to reset.
The LTC1644 is designed to turn a board’s supply voltages
on and off in a controlled manner, allowing the board to be
safely inserted or removed from a live CPCI slot without
glitching the system power supplies. The chip also protects
the supplies from shorts, precharges the bus I/O pins during
insertion and extraction and monitors the supply voltages.
The LTC1644 is specifically designed for CPCI applica-
tions where the chip resides on the plug-in board.
LTC1644 Feature Summary
• Allows safe board insertion and removal from a CPCI
backplane.
• Controls all four CPCI supplies: –12V, 12V, 3.3V and 5V.
• Adjustable foldback current limit: an adjustable analog
current limit with a value that depends on the output
voltage. If the output is shorted to ground, the current
limit drops to keep power dissipation and supply glitches
to a minimum.
• 12V and –12V circuit breakers: if either supply remains
in current limit too long, the circuit breaker will trip, the
supplies are turned off and the FAULT pin is pulled low.
• Dual-level, adjustable 5V and 3.3V circuit breakers: if
either supply exceeds current limit for too long, the
circuit breaker will trip, the supplies will be turned off
and the FAULT pin will be asserted. In the event that
either supply exceeds 3 times the nominal current level,
all supplies will be turned off and the FAULT pin will be
asserted immediately.
• Current limit during power up: the supplies are allowed
to power up in current limit. This allows the chip to
power up boards with widely varying capacitive loads
without tripping the circuit breaker. The maximum
allowable power-up time is adjustable using the TIMER
pin.
• 12V and –12V power switches on chip.
• PWRGD output: monitors the voltage status of the four
supply voltages.
• PCI_RST# combined on-chip with HEALTHY# to create
LOCAL_PCI_RST# output. If HEALTHY# deasserts,
LOCAL_PCI_RST# is asserted independent of
PCI_RST#.
• Precharge output: on-chip reference and amplifier pro-
vide 1V for biasing bus I/O connector pins during CPCI
card insertion and extraction.
• Space saving 20-pin SSOP package.
CPCI Power Requirements
CPCI systems usually require four power rails: 5V, 3.3V,
12V and –12V. The tolerance of the supplies as measured
at the components on the plug-in card is summarized in
Table 1.
Table 1. Compact PCI Power Specifications
SUPPLY
5V
TOLERANCE
+ 5%/– 3%
MAX RIPPLE (_P-P)
50mV
3.3V
+ 5%/– 3%
50mV
12V
±5%
240mV
– 12V
±5%
240mV
1644f
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