LTC4216
9
4216fa
For more information www.linear.com/LTC4216
applicaTions inForMaTion
Hot Circuit Insertion
When circuit boards are inserted into a live backplane, the
supply bypass capacitors can draw huge transient current
from the power bus as they charge. Potentially, the flow
of current could damage the connector pins and glitch
the power bus, causing other boards in the system to
reset. The LTC4216 is designed to turn on or off a circuit
board supply in a controlled manner, allowing insertion
or removal without glitches or connector damage.
Overview of LTC4216 Features
1. Allows safe board insertion and removal from a live
backplane.
2. Controls load voltages from 0V to 6V.
3. High side gate drive for external N-channel MOSFET.
4. Adjustable soft-start with inrush current limiting for
large load capacitor during start-up.
5. Adjustable analog current limit (ACL) with circuit
breaker fault time-out during an overcurrent fault condi
-
tion. No external gate capacitor is required for the ACL
loop compensation.
6. Electronic circuit breaker tripping at 25mV across the
sense resistor. The response time is adjustable through
an external capacitor at the FILTER pin.
7. Provides an ON pin to turn on and off the device. This can
also be used to reset the device after a
circuit breaker trip.
8. Provides output supply voltage monitoring through the
FB pin and signals the RESET pin output.
9. Provides fault status output.
ON Control
The ON pin has two hysteretic comparators with differ
-
ent threshold levels (0.8V and 0.4V) and they serve two
purposes:
1. Turn on the device if the ON pin voltage > 0.8V for more
than 6µs and turn it off if the ON pin voltage < 0.72V for
more than 15µs.
2. Reset the device if the ON pin voltage < 0.4V for more
than 30µs after a circuit breaker trip.
There are various methods of setting the ON pin
voltage:
1. Ti
e
the ON pin to the load supply (V
IN
) through a 10k
pull-up resistor.
2. Drive the ON pin with an ON/OFF logic signal from the
system controller.
3. Connect an external resistive divider at the ON pin.
This divider can be used to set a higher value for the load
supply undervoltage lockout voltage than the internal V
CC
undervoltage lockout circuit.
For example, as shown in Figure 17, if both V
CC
and
SENSEP pins are connected to a 5V load supply, choosing
the resistive divider values, R1 = 20k, R2 = 80.6k, turns on
the device when
the load supply voltage reaches around
80% of its final value.
V
CC
Undervoltage Lockout
A hysteretic comparator, UVLO, monitors bias supply (V
CC
)
for undervoltage. The thresholds are defined by V
CC(UVL)
(2.12V) and its hysteresis, ΔV
CC(UVL,HYST)
(120mV). When
V
CC
rises above V
CC(UVL)
, the device is enabled. When
V
CC
falls below (V
CC(UVL)
– ΔV
CC(UVL,HYST)
), the device is
disabled and GATE is pulled low. If V
CC
cycles below this
threshold for more than 200µs, following a circuit breaker
trip, it clears the fault latch. Any bias supply glitches that
last less than 10µs will be rejected by the UVLO glitch filter.
Timer
An external capacitor, C1, is used at TIMER pin to provide
two timing cycles for the LTC4216. The first timing cycle
is the debounce cycle when the ON pin is first turned on,
both the GATE and SS pins are held low and any short-
circuit faults are ignored by the electronic circuit breaker.
Second timing cycle is the power-good delay before the
RESET pin goes high when the FB pin voltage exceeds
0.6V and its hysteresis.
The TIMER pin sources 2µA into C1 during
the two timing
cycles
and is then pulled low by an internal N-channel
