LTC4211
27
4211fc
For more information www.linear.com/LTC4211
APPLICATIONS INFORMATION
+
V
CC
SENSE
LTC4211
8
2
3 4
7 6
C
LOAD
V
OUT
12V
3A
GND
4211 F17
5
1
R4
12.4k
GATE
GNDTIMER
PCB CONNECTION SENSE
C
TIMER
8.2nF
FB
ON
SHORT
LONG
V
CC
12V
GND
LONG
Z1 = 1SMA12A OR SMAJ12A
** HIGHLY RECOMMENDED
RESET
R2
10k
R1
61.9k
R
X
10Ω
R
SENSE
0.012Ω
PCB EDGE
CONNECTOR
(MALE)
M1
Si4410DY
Z1**
R
G
100Ω
R3
93.1k
R5
10k
µP
LOGIC
RESET
C
X
100nF
BACKPLANE
CONNECTOR
(FEMALE)
12V Hot Swap Application
Figure 17 shows a 12V, 3A hot swap application circuit.
The resistive divider R1/R2 programs the undervoltage
lockout externally and allows the system to start up after
V
CC
increases above 9.46V. The resistive divider R3/R4
monitors V
OUT
and signals the RESET pin when V
OUT
goes above 10.54V. Transient voltage suppressor Z1 and
snubber network (C
X
, R
X
) are highly recommended to
protect the 12V applications system from ringing and
voltage spikes. R
G
is recommended for V
CC
> 10V and it
can minimize high frequency parasitic oscillations in the
power MOSFET.
AUTORETRY AFTER A FAULT
To configure the LTC4211 to automatically retry after a
fault condition, the FAULT and ON pins can be connected
to a pull-up resistor (R
AUTO
) to the supply, as shown in
Figure 17. 12V Hot Swap Application
Figure 18. In this case, the autoretry circuitry will attempt
to restart the LTC4211 with a 50% duty cycle, as shown
in the timing diagram of Figure 19. To prevent overheat
-
ing the external MOSFET and other components during
the autoretry sequence, adding a capacitor (C
AUTO
) to the
circuit introduces an RC time constant (t
OFF
) that adjusts
the autoretry duty cycle. Equation 14 gives the autoretry
duty cycle, modified by this external time constant:
Autoretry Duty Cycle ≈
t
TIMER
t
OFF
+ 2 • t
TIMER
• 100%
(14)
where t
TIMER
= LTC4211 system timing(see TIMER func-
tion) and t
OFF
is a time needed to charge capacitor C
AUTO
from 0V to the ON pin threshold (1.316V).
In Figure 18 with R
AUTO
= 1M, the external RC time constant
is set at 1 second, the t
TIMER
delay equals 6.2ms and the
autoretry duty cycle drops from 50% to 2.5%.
Figure 18. LTC4211MS Autoretry Application
FAULT
V
CC
LTC4211MS
SENSE
GATE
FB
1
2
3
4
5
10
R
SENSE
0.007Ω
Q1
Si4410DY
9
8
7
6
RESET
ON
FILTER
TIMER
C
TIMER
10nF
GND
C
FILTER
100pF
R
AUTO
(SEE NOTE)
R
PULL-UP
10k
C
AUTO
1µF
R3
10Ω
Z1*
NOTE:
Q1 MOUNTED TO 300mm
2
COPPER AREA
R
AUTO
= 1M YIELDS 2.5%
DUTY CYCLE AND Q1 T
CASE
= 50°C
R
AUTO
= 3.2M YIELDS 0.8%
DUTY CYCLE AND Q1 T
CASE
= 37°C
Z1 = 1SMA10A OR SMAJ10A
* OPTIONAL
4211 F18
C1
0.1µF
R1
36k
V
OUT
5V
5A
C
LOAD
R2
15k
+
LONG
V
CC
5V
GND
RESET
LONG
PCB EDGE
CONNECTOR
(MALE)
BACKPLANE
CONNECTOR
(FEMALE)
SHORT
