LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 22

• Manufacturer Part Number: LTC1647
• Description: Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

LTC4211
Table 3. I
OPERATION
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
and occurs should a load current fault condition exist for
more than 20μs. 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 the electronic circuit
breaker trips for common values for R
in Table 3.
22
Table 2. t
CB(FAST)
I
I
TRIP(SLOW)
TRIP(FAST)
0.005Ω
0.006Ω
0.007Ω
0.008Ω
0.009Ω
R
0.01Ω
TRIP(SLOW)
SLOWCOMP
SENSE
= 150mV, and occurs during fast load current
1000pF
C
100pF
220pF
330pF
470pF
680pF
820pF
FILTER
=
=
V
vs C
and I
V
R
CB(FAST)
CB(SLOW)
R
SENSE
SENSE
FILTER
TRIP(FAST)
I
TRIP(SLOW)
=
8.3A
7.1A
6.3A
5.6A
10A
5A
=
R
150mV
vs R
R
SENSE
50mV
SENSE
SENSE
t
CB(SLOW)
SLOWCOMP
SENSE
156μs
224μs
310μs
440μs
527μs
638μs
82μs
CC
I
TRIP(FAST)
and SENSE
are shown
30A
25A
21A
19A
17A
15A
= 50mV,
(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 resis-
tor. PCB layout should be balanced and symmetrical to
minimize 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 accommodate
steady-state fault current levels so that the component 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
Figure 11. Making PCB Connections to the Sense Resistor
I
I
0.03" PER AMP
TRIP(NOM)
TRIP(MIN)
R
and SENSE pins are strongly recommended. The
SENSE(MAX)
=
CURRENT FLOW
=
R
SENSE
TO LOAD
R
SENSE(MAX)
= R
V
SENSE(NOM)
V
CB(MIN)
W
CB(NOM)
SENSE(NOM)
value, the nominal load current that
IRC-TT SENSE RESISTOR
LR251201R010F
OR EQUIVALENT
=
0.01, 1%, 1W
=
V
TO
CC
R
R
SENSE(MAX)
SENSE(NOM)
SENSE
⎡
⎢
⎢
⎣
40mV
TO
1+
50mV
⎛
⎜
⎝
R
100
TOL
CURRENT FLOW
⎞
⎟
⎠
TO LOAD
⎤
⎥
⎥
⎦
4211 F11
(10)
(11)
4211fb