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LTC4214-2CMS Datasheet(PDF) 8 Page - Linear Technology

Part # LTC4214-2CMS
Description  Negative Low Voltage Hot Swap Controllers
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LTC4214-2CMS Datasheet(HTML) 8 Page - Linear Technology

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LTC4214-1/LTC4214-2
8
421412f
VIN (Pin 1): Positive Supply Input. Connect this pin to the
positive side of the supply via a resistor. An internal
undervoltage lockout (UVLO) circuit holds GATE low until
the VIN pin is greater than VLKO (5.1V), overriding UV and
OV. If UV is high, OV is low and VIN comes out of UVLO,
TIMER starts an initial timing cycle before initiating a GATE
ramp-up. If VIN drops below approximately 4.8V, GATE
pulls low immediately.
PWRGD (Pin 2): Power Good Status Output. At start-up,
PWRGD latches low if DRAIN is below 1.232V and GATE
is within 2.8V of VIN. PWRGD status is reset by UV, VIN
(UVLO) or a circuit breaker fault timeout. This pin is
internally pulled high by a 50
µA current source.
SS (Pin 3): Soft-Start Pin. This pin is used to ramp inrush
current during start up, thereby effecting control over di/
dt. A 20x attenuated version of the SS pin voltage is
presented to the current limit amplifier. This attenuated
voltage limits the MOSFET’s drain current through the
sense resistor during the soft-start current limiting. At the
beginning of a start-up cycle, the SS capacitor (CSS) is
ramped by a 22
µA current source. The GATE pin is held
low until SS exceeds 20 • VOS = 0.2V. SS is internally
shunted by a 73k resistor (RSS) which limits the SS pin
voltage to 1.6V. This corresponds to an analog current
limit SENSE voltage of 70mV. If the SS capacitor is
omitted, the SS pin ramps from 0V to 1.6V in about 220
µs.
The SS pin is pulled low under any of the following
conditions: in UVLO, in an undervoltage condition, in an
overvoltage condition, during the initial timing cycle or
when the circuit breaker fault times out.
SENSE (Pin 4): Circuit Breaker/Current Limit Sense Pin.
Load current is monitored by a sense resistor RS con-
nected between SENSE and VEE, and controlled in three
steps. If SENSE exceeds VCB (50mV), the circuit breaker
comparator activates a (40
µA + 8 • IDRN) TIMER pull-up
current. If SENSE exceeds VACL (70mV), the analog cur-
rent limit amplifier pulls GATE down to regulate the MOSFET
current at VACL/RS. In the event of a catastrophic short-
circuit, SENSE may overshoot 70mV. If SENSE reaches
VFCL (200mV), the fast current limit comparator pulls
GATE low with a strong pull-down. To disable the circuit
breaker and current limit functions, connect SENSE to VEE.
VEE (Pin 5): Negative Supply Voltage Input. Connect this
pin to the negative side of the power supply.
GATE (Pin 6): N-Channel MOSFET Gate Drive Output. This
pin is pulled high by a 50
µA current source. GATE is pulled
low by invalid conditions at VIN (UVLO), UV, OV, or a circuit
breaker fault timeout. GATE is actively servoed to control
the fault current as measured at SENSE. A compensation
capacitor at GATE stabilizes this loop. A comparator
monitors GATE to ensure that it is low before allowing an
initial timing cycle, GATE ramp-up after an overvoltage
event or restart after a current limit fault. During GATE
start-up, a second comparator detects if GATE is within
2.8V of VIN before PWRGD is set.
DRAIN (Pin 7): Drain Sense Input. DRAIN measures the
drain-source voltage of the external N-channel MOSFET
switch for two purposes: first, a comparator detects when
VDS < 1.232V and together with the GATE high compara-
tor, controls the status of the PWRGD output. Second, if
VDS is greater than the DRAIN clamp of approximately
4.2V (VDRNCL), the current through resistor RD is multi-
plied by 8 and added to the TIMER’s 40
µA pull-up current
during a circuit breaker fault cycle. This reduces the
fault time and MOSFET heating under conditions of high
dissipation.
OV (Pin 8): Overvoltage Input. The active high threshold at
the OV pin is set at 3V with respect to VEE and exhibits
0.15V hysteresis. If OV > 3V, GATE pulls low. When OV
returns below 2.85V, GATE start-up begins without an
initial timing cycle. If an overvoltage condition occurs in
the middle of an initial timing cycle, the initial timing cycle
is restarted after the overvoltage condition goes away. An
overvoltage condition does not reset the PWRGD flag. The
internal UVLO at VIN always overrides OV. A 1nF to 10nF
capacitor at OV prevents transients and switching noise
from affecting the OV thresholds and prevents glitches at
the GATE pin.
PI FU CTIO S


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