LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 31

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

APPLICATIONS INFORMATION
SUPPLY OVERVOLTAGE DETECTION/
PROTECTION USING FILTER PIN
In addition to using external protection devices around the
LTC4211 for large scale transient protection, low power
Zener diodes can be used with the LTC4211’s FILTER
pin to act as a supply overvoltage detection/protection
circuit on either the high side (input) or low side (output)
of the external pass transistor. Recall that internal control
circuitry keeps the LTC4211 GATE voltage from ramping
up if V
(V
High Side (Input) Overvoltage Protection
As shown in Figure 23, a low power Zener diode can
be used to sense an overvoltage condition on the input
(high) side of the main 5V supply. In this example, a low
bias current 1N4691 Zener diode is chosen to protect the
system. Here, the Zener diode is connected from V
the LTC4211’s FILTER pin (Pin 3 MS). If the input volt-
age to the system is greater than 6.8V during start-up,
the voltage on the FILTER pin is pulled higher than its
1.156V threshold. As a result, the GATE pin is not allowed
to ramp and the second timing cycle will not commence
until the supply overvoltage condition is removed. Should
the supply overvoltage condition occur during normal
FILTER
ON/OFF
RESET
FAULT
GND
FILTER
5V
> 1.236V) causes FAULT to be asserted low.
CONNECTOR
BACKPLANE
(FEMALE)
> 1.156V, or when an external fault condition
CONNECTOR
PCB EDGE
(MALE)
Figure 23. LTC4211MS High Side Overvoltage Protection Implementation
LONG
SHORT
SHORT
SHORT
LONG
R4
10k
10k
R6
Z1*
R5
10k
R7
10k
R3
10Ω
6.2V
C1
0.1μF
Z2
C
47pF
FILTER
CC
to
C
10nF
operation, internal control logic would trip the electronic
circuit breaker and the GATE would be pulled to ground,
shutting OFF the external pass transistor. If a lower supply
overvoltage threshold is desired, use a Zener diode with
a smaller breakdown voltage.
A timing diagram for illustrating LTC4211 operation under a
high side overvoltage condition is shown in Figure 24. The
start-up sequence in this case (between Time Points 1 and
2) is identical to any other start-up sequence under normal
operating conditions. At Time Point 2A, the input supply
voltage causes the Zener diode to conduct thereby forcing
V
and the TIMER pin voltage ramps down. At Time Point 4,
the LTC4211 checks if V
low (but not latched) to indicate a start-up failure. The
start-up sequence only resumes with the second timing
cycle at Time Point 5 when the input overvoltage condition
is removed. At this point in time, the GATE pin voltage is
allowed to ramp up, FAULT is pulled to logic high and the
circuit breaker is armed. At any time after Time Point 5,
should a supply overvoltage condition develop (V
1.236V), the electronic circuit breaker will trip, the GATE
will be pulled low to turn off the external MOSFET and
FAULT will be asserted low and latched. This sequence is
shown in detail at Time Point B.
TIMER
FILTER
1
2
3
4
5
> 1.156V. At Time Point 3, FAULT is asserted low
RESET
ON
FILTER
TIMER
GND
LTC4211
SENSE
FAULT
GATE
Z1 = 1SMA10A OR SMAJ10A
Z2 = 1N4691
* OPTIONAL
V
CC
FB
10
9
8
7
6
FILTER
0.007Ω
R
SENSE
< 1.156V. FAULT is asserted
Si4410DY
Q1
4211 F23
LTC4211
R1
36k
R2
15k
+
C
LOAD
FILTER
31
V
5V
5A
OUT
4211fb
>