LTC1644CGN#TR Linear Technology, LTC1644CGN#TR Datasheet - Page 14

• Manufacturer Part Number: LTC1644CGN#TR
• Description: IC CONTROLLER HOT SWAP 20-SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC1644CGN#TR

• Applications: CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, ±12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP (0.154", 3.91mm Width)
• Family Name: LTC1644
• Package Type: SSOP N
• Operating Supply Voltage (min): 2.75/10.8/-10.8V
• Operating Supply Voltage (max): 13.2/-14V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 3.99mm
• Product Height (mm): 1.5mm
• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC1644CGNTR

APPLICATIO S I FOR ATIO
LTC1644
Table 2. t
The TIMER pin is immediately pulled low when the BD_SEL#
signal goes high.
Thermal Shutdown
The internal switches for the 12V and –12V supplies are
protected by an internal current limit and a thermal shut-
down circuit. When the temperature of the chip reaches
130 C, all switches will be latched off and the FAULT pin
(Pin 6) will be pulled low.
Short-Circuit Protection
During a normal power-up sequence, if the TIMER (Pin 4)
is done ramping and any supply is still in current limit, all
of the pass transistors will be immediately turned off and
FAULT (Pin 6) will be pulled low as shown in Figure 4.
In order to prevent excessive power dissipation in the pass
transistors and to prevent 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 large
currents can flow before the breaker trips, the current
foldback feature assures that the supply current will be
kept at a safe level. In addition, current foldback prevents
voltage glitches when powering up into a short.
If either the 12V or –12V supply exceeds current limit after
power up, the shorted supply’s current will drop immedi-
ately to its I
limit for more that 45 s, all of the supplies will be latched
off. The 45 s delay prevents quick current spikes—for
example, from a fan turning on—from causing false trips
of the circuit breaker.
14
0.022 F
0.033 F
0.047 F
0.068 F
0.082 F
C
0.01 F
0.1 F
TIMER
TIMER
LIMIT
vs C
TIMER
value. If that supply remains in current
5.24ms
11.5ms
17.3ms
24.6ms
35.6ms
43.0ms
52.4ms
t
U
TIMER
U
C
0.22 F
0.33 F
0.47 F
0.68 F
0.82 F
TIMER
1 F
W
U
115ms
173ms
246ms
356ms
430ms
524ms
t
TIMER
After power-up, the 5V and 3.3V supplies are protected
from overcurrent and short-circuit conditions by dual-
level circuit breakers. In the event that either supply
current exceeds the nominal limit but is less than 3 times
the current limit, an internal timer is started. If the supply
is still overcurrent after 45 s, the circuit breaker trips and
all the supplies are turned off (Figure 5). If a short-circuit
occurs and the supply current exceeds 3 times the set
limit, the circuit breakers trip without any delay and the
chip latches off (Figure 6). The chip will stay in the latched
off state until OFF/ON (Pin 5) is cycled high then low or the
12V
The current limit and the foldback current level for the 5V
and 3.3V outputs are both a function of the external sense
resistor (R1 for 3V
shown in Figure 1, a sense resistor is connected between
5V
the 3V supply, a sense resistor is connected between 3V
(Pin 9) and 3V
foldback current level are given by Equations 4 and 5:
where XV
As a design aid, the current limit and foldback level for
commonly used values for R
Table 3. I
where XV
The current limit for the internal 12V switch is set at
840mA folding back to 360mA and the –12V switch at
320mA folding back to 100mA.
R
IN
I
I
LIMIT XVOUT
FOLDBACK XVOUT
SENSE
IN
0.005
0.006
0.007
0.008
0.009
(Pin 13) and 5V
0.01
(Pin 1) power supply is cycled off then on.
(
LIMIT(XVOUT)
( )
OUT
OUT
(
= 3V
= 5V
)
SENSE
R
OUT
OUT
)
OUT
and I
SENSE XVOUT
I
LIMIT(XVOUT)
SENSE
(Pin 10). The current limit and the
R
51
10.2A
and R2 for 5V
or 5V
or 3V
8.5A
7.3A
6.4A
5.7A
5.1A
FOLDBACK(XVOUT)
SENSE XVOUT
mV
(
12
(Pin 12) for the 5V supply. For
OUT
OUT
mV
(
SENSE
)
.
.
)
is shown in Table 3.
OUT
vs R
, see Figure 1). As
I
FOLDBACK(XVOUT)
SENSE
2.4A
2.0A
1.7A
1.5A
1.3A
1.2A
1644f
(4)
(5)
IN