LTC4245CUHF#PBF Linear Technology, LTC4245CUHF#PBF Datasheet - Page 19

• Manufacturer Part Number: LTC4245CUHF#PBF
• Description: IC CNTRLR HOT SWAP 38-QFN
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4245CUHF#PBF

• Applications: CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 38-WFQFN, Exposed Pad
• Family Name: LTC4245
• Package Type: QFN EP
• Operating Supply Voltage (min): 2.25/4.25/10.2/-10.2V
• Operating Supply Voltage (max): 0/10/20/-20V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 5mm
• Product Length (mm): 7mm
• Mounting: Surface Mount
• Pin Count: 38
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
After the switches are turned off, the TIMER pin begins
charging up with a 2μA pull-up current. When it reaches
2.56V it is reset to ground with a switch. During this cool-
down cycle, the overcurrent fault bit cannot be reset. After
this cycle, the switches will be allowed to turn on again if
the overcurrent fault bit is cleared. However, if the over-
current autoretry bit, C1, has been set then the switches
turn on again automatically after the 100ms turn-on delay
(without resetting the overcurrent fault).
After start-up, a supply has dual-level glitch-tolerant
protection against overcurrent faults. The sense resistor
voltage drop is monitored by an electronic circuit breaker
(ECB) and an active current limit (ACL). In the event that
a supply’s current exceeds the ECB threshold, an internal
timer is started. If the supply is still overcurrent after 22μs,
the ECB trips and all supplies are turned off (Figure 7). An
analog current limit loop prevents the supply current from
exceeding 3x the ECB threshold in the event of a short
circuit (Figure 8). The 22μs fi lter delay and the higher
ACL threshold prevents unnecessary resets of the board
due to minor current surges. The LTC4245 will stay in the
latched off state unless bit C1 is set, in which case the
switches turn on after a 100ms delay. Note that foldback
is not active after start-up.
Undervoltage Fault
An undervoltage fault occurs when any of the input sup-
plies falls below its undervoltage threshold for more
than 3.5μs (5.5μs for V
immediately and sets the undervoltage present bit A0 and
the corresponding undervoltage fault bit (bits E0 to E3).
5V SUPPLY
CURRENT
Figure 7. Overcurrent Fault on 5V Output
5V
5A/DIV
2V/DIV
2V/DIV
5V
GATE
OUT
U
EEIN
U
TIME 10µs/DIV
). This turns off all switches
W
4245 F07
U
If the supply subsequently rises above the threshold for
100ms, the switches will turn on again unless the under-
voltage auto-retry has been disabled by clearing bit C0.
When power is fi rst applied to the device, if any supply is
below its threshold after INTV
lockout threshold, an undervoltage fault will be logged in
the FAULT1 register.
PGI Fault
The PGI pin can be used to shut off the board’s input sup-
plies in case downstream supplies fail to enter regulation
in time. It can be tied to the reset output of a monitor IC
or the powergood pin of a DC/DC converter.
After all supply outputs have been powered up, a timing
cycle is started with a 10μA current pulling up the TIMER
pin. When TIMER reaches 2.56V it is reset to ground by a
switch. As TIMER falls below 0.23V, the PGI pin is sampled.
If it is low, the PGI fault bit F4 is set and all external FETs
are shut off. A cool-down timing cycle is started using
a 2μA pull-up current on TIMER pin. Bit F4 cannot be
reset during this time. After this cycle, the switches will
be allowed to turn on again if the PGI fault bit is cleared.
However, if the PGI autoretry bit, C4, has been set then
the switches turn on again automatically after the 100ms
turn-on delay.
By default, the PGI pin is ignored during normal operation.
It can be enabled by clearing PGI disable bit C3. Now, if
PGI pin goes low for more than 20μs, all FETs will be
shut off. If bit C4 is set, the switches will turn on after the
100ms turn-on delay.
12V SUPPLY
Figure 8. Short-Circuit Fault on 12V Output
CURRENT
12V
12V
2A/DIV
5V/DIV
5V/DIV
GATE
OUT
TIME 5µs/DIV
CC
crosses its undervoltage
LTC4245
4245 F08
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