LTC4213 Linear Technology, LTC4213 Datasheet - Page 14

• Manufacturer Part Number: LTC4213
• Description: Electronic Circuit Breaker
• Manufacturer: Linear Technology

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LTC4213
APPLICATIO S I FOR ATIO
Operating temperature of 0° to 70°C.
MOSFET resistance variation:
V
The current limits are:
For proper operation, the minimum current limit must
exceed the circuit maximum operating load current with
margin. So this system is suitable for operating load
current up to 1A. From this calculation, we can start with
the general rule for MOSFET R
mum operating load current is roughly half of the
I
Note that the R
operating ∆V
Table 1 gives the nominal operating ∆V
various operating V
the MOSFET’s data sheet to obtain the R
14
LIMIT(NOM)
CB
R
R
R
R
R
R
NOM V
MIN V
MAX V
I
I
I
I
LIMIT(NOM)
LIMIT(MIN)
LIMIT(MAX)
OPMAX
DSON
DSON
DSON
DSON(NOM)
DSON(MAX)
DSON(MIN)
variation:
CB
CB
@ 25°C = 100%
@ 0°C = 90%
@ 70°C = 120%
CB
. Equation 7 shows the rule of thumb.
=
= 22.5mV = 90%
= 27.5mV = 110%
= 25mV = 100%
2
GSMAX
= 22.5mV/22.3mΩ = 1.01A
= 27.5mV/7.2mΩ = 3.82A
= 25mV/12.3mΩ = 2.03A
= 15m • 0.667 • 0.80 • 0.90 = 15m • 0.480
= 7.2mΩ
•
= 15m • 1.333 • 0.93 • 1.2 = 15m • 1.488
= 22.3mΩ
= 15m • 0.82 = 12.3mΩ
R
V
DSON(NOM)
CB NOM
DSON NOM
U
(
CC
rather than at typical vendor spec.
. From this table users can refer to
(
)
U
)
is at the LTC4213 nominal
DSON
W
by assuming maxi-
DSON(NOM)
GSMAX
U
at the
value.
( )
7
Table 1. Nominal Operating ∆V
Supply Voltage
Load Supply Power-Up after Circuit Breaker Armed
Figure 4 shows a normal power-up sequence for the
circuit in Figure 1 where the V
circuit breaker is armed. V
auxiliary bias supply. V
point 1. V
debounce delay, the GATE pin starts ramping up at time
point 3. The external MOSFET starts conducting at time
point 4. At time point 5, V
circuit breaker is armed. After 50µs (t
pulls high by an external resistor at time point 6. READY
signals the V
load supply begins soft-start ramp at time point 7. The load
supply ramp rate must be slow to prevent circuit breaker
tripping as in equation (8).
Where I
by equation 7.
For illustration, V
nominal operating ∆V
current is 3.5A (refer to equation 7). Assuming the load
can draw a current of 2A at power-up, there is a margin of
1.5A available for C
be <15V/ms. At time point 8, the current through the
MOSFET reduces after C
∆
∆
V
IN
t
OPMAX
<
ON
I
V
OPMAX
CC
IN
2.3
2.5
2.7
3.0
3.3
5.0
6.0
exceeds 0.8V at time point 2. After a 60µs
(V)
is the maximum operating current defined
load supply module to start its ramp. The
C
LOAD
CB
LOAD
−
= 25mV and R
I
LOAD
GSMAX
of 100µF and V
LOAD
CC
GATE
GSMAX
CC
IN
rises above 2.07V at time
. The maximum operating
is fully charged.
load supply power-up after
is first powered up by an
exceed ∆V
for Typical Bias
DSON
READY
∆V
IN
GSMAX
ramp rate should
= 3.5mΩ at the
4.3
5.0
5.6
6.5
7.0
7.0
7.0
GSARM
delay), READY
(V)
and the
4213f
( ) 8