LTC4211 LINER [Linear Technology], LTC4211 Datasheet - Page 21

• Manufacturer Part Number: LTC4211
• Description: Hot Swap Controller with Multifunction Current Control
• Manufacturer: LINER [Linear Technology]

OPERATIO
Table 2. t
SENSE RESISTOR CONSIDERATIONS
The fault current level at which the LTC4211’s internal
electronic circuit breaker trips is determined by a sense
resistor connected between the LTC4211’s V
pins and two separate trip points. The first trip point is set
by the SLOW COMP’s threshold, V
occurs should a load current fault condition exist for more
than 20 s. The current level at which the electronic circuit
breaker trips is given by Equation 8:
The second trip point is set by the FAST COMP’s threshold,
V
transients that exist for 300ns or longer. The current level
at which the circuit breaker trips in this case is given by
Equation 9:
As a design aid, the currents at which electronic circuit
breaker trips for common values for R
Table 3.
Table 3. I
CB(FAST)
I
I
TRIP SLOW
TRIP FAST
0.005
0.006
0.007
0.008
0.009
R
0.01
(
(
SENSE
SLOWCOMP
TRIP(SLOW)
= 150mV, and occurs during fast load current
C
1000pF
100pF
220pF
330pF
470pF
680pF
820pF
FILTER
)
)
V
vs C
U
V
and I
R
CB FAST
CB SLOW
R
SENSE
(
SENSE
FILTER
(
TRIP(FAST)
I
TRIP(SLOW)
)
8.3A
7.1A
6.3A
5.6A
10A
)
5A
150
R
vs R
R
SENSE
50
SENSE
mV
SENSE
CB(SLOW)
mV
SENSE
t
SLOWCOMP
156 s
224 s
310 s
440 s
527 s
638 s
82 s
CC
I
= 50mV, and
are shown in
TRIP(FAST)
and SENSE
30A
25A
21A
19A
17A
15A
(8)
(9)
For proper circuit breaker operation, Kelvin-sense PCB
connections between the sense resistor and the LTC4211’s
V
drawing in Figure 11 illustrates the correct way of making
connections between the LTC4211 and the sense resistor.
PCB layout should be balanced and symmetrical to mini-
mize wiring errors. In addition, the PCB layout for the
sense resistor should include good thermal management
techniques for optimal sense resistor power dissipation.
The power rating of the sense resistor should accommo-
date steady-state fault current levels so that the compo-
nent is not damaged before the circuit breaker trips.
Table 4 in the Appendix lists sense resistors that can be
used with the LTC4211’s circuit breaker.
CALCULATING CIRCUIT BREAKER TRIP CURRENT
For a selected R
trips the circuit breaker is given by Equation 10:
The minimum load current that trips the circuit breaker is
given by Equation 11.
where
CC
TRACK WIDTH W:
ON 1 OZ COPPER
I
I
R
Figure 11. Making PCB Connections to the Sense Resistor
0.03" PER AMP
TRIP NOM
TRIP MIN
SENSE MAX
and SENSE pins are strongly recommended. The
(
(
(
)
)
CURRENT FLOW
)
SENSE
R
TO LOAD
R
SENSE MAX
V
SENSE NOM
V
R
CB MIN
W
CB NOM
SENSE NOM
(
value, the nominal load current that
(
(
(
)
(
IRC-TT SENSE RESISTOR
)
)
)
OR EQUIVALENT
LR251201R010F
0.01 , 1%, 1W
V
)
TO
CC
R
• 1
R
SENSE MAX
SENSE NOM
SENSE
40
TO
50
mV
mV
(
R
100
(
TOL
LTC4211
)
CURRENT FLOW
)
TO LOAD
21
4211 F11
(10)
(11)
4211f