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LTC4210-1IS6#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
LTC4210 -1/LTC4210 -2
13
421012fa
For more information www.linear.com/LTC4210-1
APPLICATIONS INFORMATION
The current through R
SENSE
can be divided into two com-
ponents; I
CLOAD
due to the total load capacitance (C
LOAD
)
and I
LOAD
due to the noncapacitive load elements. The
capacitive load typically dominates.
For a successful start-up without current limit, I
RSENSE
< I
LIMIT
:
I
RSENSE
= I
CLOAD
+ I
LOAD
< I
LIMIT
I
RSENSE
= C
LOAD
•
∆V
OUT
∆T
+I
LOAD
<I
LIMIT
(7)
Due to the voltage follower configuration, the V
OUT
ramp
rate approximately tracks V
GATE
:
∆V
OUT
∆T
=
I
CLOAD
C
LOAD
≈
∆V
GATE
∆T
=
I
GATE
C
GATE
(8)
At time point 6, V
OUT
is approximately V
IN
but GATE
ramp-up continues until it reaches a maximum voltage.
This maximum voltage is determined either by the charge
pump or the internal clamp.
Start-Up Cycle with Current Limit
If the duration of the current limit is brief during start-up
(Figure 4) and it did not last beyond the circuit breaker
function time out, the GATE behaves the same as in start-up
without current limit except for the time interval between
time point 5A and time point 5B. The servo amplifier limits
I
RSENSE
by decreasing the I
GATE
current (<10µA).
I
RSENSE
=I
LIMIT
=
50mV
R
SENSE
(9)
Equations 7 and 8 are applicable but with a lower GATE
and V
OUT
ramp rate.
Gate Start-Up Time
The start-up time without current limit is given by:
t
STARTUP
=C
GATE
•
V
TH
+V
IN
I
GATE
t
STARTUP
=C
GATE
•
V
TH
I
GATE
+C
GATE
•
V
IN
I
GATE
(10)
During current limiting, the second term in Equation 10
is partly modified from C
GATE
• V
IN
/I
GATE
to C
LOAD
• V
IN
/
I
CLOAD
. The start-up time is now given by:
t
STARTUP
=C
GATE
•
V
TH
I
GATE
+C
LOAD
•
V
IN
I
CLOAD
=C
GATE
•
V
TH
I
GATE
+C
LOAD
•
V
IN
I
RSENSE
–I
LOAD
(11)
For successful completion of current limit start-up cycle
there must be a net current to charge C
LOAD
and the cur-
rent limit duration must be less than t
CBDELAY
. The second
term in Equation 11 has to fulfill Equation 12.
C
LOAD
•
V
IN
I
RSENSE
–I
LOAD
< t
CBDELAY
(12)
Figure 4. Operating Sequence with
Current Limiting at Start-Up Cycle
V
TIMER
V
GATE
V
OUT
I
RSENSE
V
ON
V
IN
>2.5V
1 2 3 4 5 5A 5B 6 7
RESET
MODE
INITIAL
CYCLE
START-UP
CYCLE
NORMAL
CYCLE
5µA
100µA
COMP1
10µA
10µA
60µA
100µA
DISCHARGE
BY LOAD
REGULATED AT 50mV/R
SENSE
V
TH
COMP2
2µA
<10µA
4210 F04
>1.3V
LTC4210 -1/LTC4210 -2
14
421012fa
For more information www.linear.com/LTC4210-1
APPLICATIONS INFORMATION
Circuit Breaker Timer Operation
When a current limit fault is encountered at time point A
in Figure 5, the circuit breaker timing is activated with a
60µA pull-up. The circuit breaker trips at time point B if
the fault is still present and the TIMER pin voltage reaches
the COMP2 threshold and the LTC4210 shuts down. For
a continuous fault, the circuit breaker delay is:
t
CBDELAY
=1.3V •
C
TIMER
60µA
(13)
Intermittent overloads may exceed the current limit as in
Figure 6, but if the duration is sufficiently short, the TIMER
pin may not reach the COMP2 threshold and the LTC4210
will not shut down. To handle this situation, the TIMER
discharges with 2µA whenever (V
CC
– SENSE) voltage is
below the 50mV limit and the TIMER voltage is between
the COMP1 and COMP2 thresholds. When the TIMER
voltage falls below the COMP1 threshold, the TIMER pin
is discharged with an equivalent 7k resistor (normal mode,
100µA source) when (V
CC
– SENSE) voltage is below
the 50mV limit. If the TIMER pin does not drop below
the COMP1 threshold, any intermittent overload with an
aggregate duty cycle of more than 3.8% will eventually
trip the circuit breaker. Figure 7 shows the circuit breaker
response time in seconds normalized to 1µF. The asym
-
metric charging and discharging of TIMER is a fair gauge
of MOSFET heating.
t
C
TIMER
(s / µF)=
1.3V •1µF
60µA •D
( )
– 2µA
(14)
When the circuit breaker trips, the GATE pin is pulled low.
The TIMER enters latchoff mode with a 5µA pull-up for the
LTC4210-2 (latched-off version), while an auto-retry “cool-
off” cycle begins with a 2µA pull-down for the LTC4210-1
(auto-retry version). An auto-retry cool-off delay of the
LTC4210-1 between COMP2 and COMP1 thresholds takes:
t
COOLOFF
=1.1V •
C
TIMER
2µA
(15)
Figure 5. A Continuous Fault Timing
Figure 7. Circuit Breaker Timer Response
for Intermittent Overload
Figure 6. Multiple Intermittent Overcurrent Condition
V
TIMER
NORMAL
MODE
FAULT
MODE
100µA
COMP1
CIRCUIT BREAKER
TRIPS
LATCHED OFF (5µA PULL-UP)
OR RETRY (2µA PULL-DOWN)
COMP2
A B
60µA
4210 F05
A1 B1 A2 B2 A3 B3
~50mV/R
SENSE
60µA
CIRCUIT BREAKER
TRIPS
COMP1
4210 F06
COMP2
I
LOAD
V
TIMER
V
GATE
2µA
CB
FAULT
CB
FAULT
CB
FAULT
2µA
LATCHED OFF (5µA PULL-UP)
OR RETRY (2µA PULL-DOWN)
60µA
60µA
10µA 10µA
OVERLOAD DUTY CYCLE, D (%)
10
NORMALIZED RESPONSE TIME (s/µF)
30
1
4210 F07
0.01
0.1
20 100
90
807060
50
40
0
(s/µF) =
t
C
TIMER
1.3V • 1µF
60µA • D – 2µA
LTC4210 -1/LTC4210 -2
15
421012fa
For more information www.linear.com/LTC4210-1
APPLICATIONS INFORMATION
Auto-Retry After Current Fault (LTC4210-1)
Figure 8 shows the waveforms of the LTC4210-1 (auto-
retry version) during a circuit breaker fault. At time point
B1, the TIMER trips the COMP2 threshold of 1.3V. The
GATE pin pulls to ground while TIMER begins a “cool-off”
cycle with a 2µA pull-down to the COMP1 threshold of
0.2V. At time point C1, the TIMER pin pulls down with
approximately a 7k resistor to ground and a GATE start-up
cycle is initiated. If the fault persists, the fault auto-retry
duty cycle is approximately 3.8%. Pulling the ON pin low
for more than 30µs will stop the auto-retry function and
put the LTC4210 in reset mode.
Latch-Off After Current Fault (LTC4210-2)
Figure 9 shows the waveforms of the LTC4210-2 (latch-off
version) during a circuit breaker fault. At time point B, the
TIMER trips the COMP2 threshold. The GATE pin pulls to
ground while the TIMER pin is latched high by a 5µA pull-
up. The TIMER pin eventually reaches the soft-clamped
voltage (V
CLAMP
) of 2.3V. To clear the latchoff mode, the
user can either pull the TIMER pin to below 0.2V externally
or cycle the ON pin low for more than 30µs.
Figure 8. Automatic Retry After Overcurrent Fault Figure 9. Latchoff After Overcurrent Fault
A1
V
TIMER
V
GATE
V
OUT
I
LOAD
4210 F08
B1 C1 A2 B2
COMP2
COMP1
CB
FAULT
CB
FAULT
NORMAL
MODE
COOL OFF
CYCLE
COOL OFF
CYCLE
60µA
100µA
2µA
2µA
60µA
REGULATING AT 50mV/R
SENSE
NORMAL
MODE
LATCHED OFF CYCLE
CB
FAULT
60µA
V
TIMER
V
GATE
V
OUT
I
LOAD
A B C
V
CLAMP
COMP2
COMP1
0V
0V
2410 F09
REGULATING AT 50mV/R
SENSE
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

LTC4210-1IS6#TRPBF

Mfr. #:
Buy LTC4210-1IS6#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
Hot Swap Voltage Controllers Hot Swap Cntr in 6-Lead SOT-23 Package
Lifecycle:
New from this manufacturer.
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