LTC4212 LINER [Linear Technology], LTC4212 Datasheet - Page 20

• Manufacturer Part Number: LTC4212
• Description: Hot Swap Controller with Power-Up Timeout
• Manufacturer: LINER [Linear Technology]

OPERATIO
LTC4212
by the SLOW COMP’s threshold, V
occurs should a load current fault condition exist for more
than 18 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 500ns 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 4.
Table 4. I
For proper circuit breaker operation, Kelvin-sense PCB
connections between the sense resistor and the LTC4212’s
V
drawing in Figure 7 illustrates the correct way of making
connections between the LTC4212 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 5 in the Appendix lists sense resistors that can be
used with the LTC4212’s circuit breaker.
20
CB(FAST)
CC
I
I
TRIP SLOW
TRIP FAST
and SENSE pins are strongly recommended. The
0.005
0.006
0.007
0.008
0.009
R
0.01
(
(
SENSE
TRIP(SLOW)
= 150mV, and occurs during fast load current
)
)
V
U
and I
V
R
CB FAST
CB SLOW
R
SENSE
(
SENSE
(
TRIP(FAST)
I
TRIP(SLOW)
)
8.3A
7.1A
6.3A
5.6A
10A
5A
)
150
R
vs R
SENSE
R
50
SENSE
mV
SENSE
CB(SLOW)
mV
SENSE
I
= 50mV, and
are shown in
TRIP(FAST)
30A
25A
21A
19A
17A
15A
(8)
(9)
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
The maximum load current that trips the circuit breaker is
given in Equation 12.
where
TRACK WIDTH W:
ON 1 OZ COPPER
I
I
R
R
0.03" PER AMP
Figure 7. Making PCB Connections to the Sense Resistor
TRIP NOM
TRIP MIN
SENSE MAX
SENSE MIN
I
TRIP MAX
(
(
(
(
(
)
)
CURRENT FLOW
)
)
)
SENSE
R
TO LOAD
R
SENSE MAX
V
R
SENSE NOM
V
R
CB MIN
R
W
SENSE NOM
CB NOM
SENSE NOM
V
SENSE MIN
(
value, the nominal load current that
CB MAX
(
(
(
(
(
)
(
IRC-TT SENSE RESISTOR
(
)
)
)
OR EQUIVALENT
LR251201R010F
)
0.01 , 1%, 1W
)
)
V
)
TO
CC
• – 1
R
• 1
R
SENSE MAX
SENSE NOM
SENSE
R
40
TO
SENSE MIN
50
60
mV
R
mV
(
R
100
100
(
mV
TOL
TOL
(
)
CURRENT FLOW
)
)
TO LOAD
4212 F07
(10)
(11)
(12)
4212f