LTC4240CGN#TRPBF Linear Technology, LTC4240CGN#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC4240CGN#TRPBF
• Description: IC CTRLR HOTSWAP CPCI I2C 28SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4240CGN#TRPBF

• Applications: CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, ±12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.150", 3.95mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4240
APPLICATIO S I FOR ATIO
Timer
During a power-up sequence, an 11.5 A current source is
connected to the TIMER pin (Pin 5) and charges up the
external TIMER pin capacitor. Current limit faults are
ignored until the TIMER voltage ramps to 5.5V. This feature
allows the LTC4240 to power-up CPCI boards with widely
varying capacitive loads on the back end supplies. The
power-up time for either of the two outputs under current
limit conditions is given by the slower of:
Where XV
be set longer than the maximum supply turn-on time but
short enough to not exceed the maximum safe operating
area of the pass transistor during a short-circuit. V
threshold voltage of the external power FET (2V – 3V). The
timer period will be:
The TIMER pin is immediately pulled low when either
OFF/ON (Pin 28) or Bit 2 of command latch (C2) goes high.
The TIMER pin also functions as a temporary auxiliary
supply for 12V
glitch on 12V
is used as substitute 12V
glitch immunity of the LTC4240.
Thermal Shutdown
The internal switches for the 12V and –12V supplies are
protected by current limit and thermal shutdown circuits.
When the temperature of the die reaches 150 C, all four
18
t
t
ON
ON
t
(
(
TIMER
GATE
XV
OUT
OUT
)
)
C
IN
C XV
= 5V
TIMER
IN
2
, the energy stored on the timer capacitor
1
11 5
(
•
. In the event of a large (greater than 1V)
I
LIMIT XVOUT
OUT
.
U
65
OUT
C
A
or 3V
LOAD XVOUT
5 5
(
A
.
V
U
V
IN
(
TH
OUT
power. This improves the
)
)
. The timer period should
–
I
LOAD XVOUT
)
W
•
XV
(
OUT
)
U
or
TH
is the
( )
( )
(3)
2
2
a
b
switches will be latched off and the FAULT pin (Pin 7) will
be pulled low. Since there is no automatic retry, power will
have to be cycled with the OFF/ON pin or the I
latch.
Short-Circuit Protection
In order to lower power dissipation in the pass transistors
and to mitigate voltage spikes on the supplies during
short-circuit conditions, the current limit on each supply
is designed to be a function of the output voltage. As the
output voltage drops, the current limit decreases. Unlike a
traditional circuit breaker function where huge currents
can flow before the breaker trips, the current foldback
feature lowers short-circuit current by at least 50% when
powering up into a short.
If any supply is in current limit after the TIMER pin voltage
has ramped to 5.5V, then all four pass transistors will be
immediately turned off and FAULT will be asserted low
(Figure 6).
BD_SEL#
10V/DIV
10V/DIV
10V/DIV
10V/DIV
12V
V
5V/DIV
5V/DIV
5V/DIV
TIMER
FAULT
5V
3V
5V/DIV
EEOUT
GATE
Figure 6. Power-Up into a Short on 3.3V Output
OUT
OUT
OUT
10ms/DIV
2
C command
4240 F06
4240f