LTC4218 Linear Technology, LTC4218 Datasheet - Page 7

• Manufacturer Part Number: LTC4218
• Description: Hot Swap Controller
• Manufacturer: Linear Technology

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PIN FUNCTIONS
Exposed Pad: Exposed pad may be left open or connected
to device ground.
FB: Foldback and Power Good Comparator Input. Connect
this pin to an external resistive divider from SOURCE for
the LTC4218 (adjustable version). The LTC4218-12 ver-
sion uses a fi xed internal divider with optional external
adjustment. Open the pin if the LTC4218-12 thresholds
for 12V operation are desired. If the voltage falls below
0.6V, the output power is considered bad and the current
limit is reduced. If the voltage falls below 1.21V the PG
pin will pull low to indicate the power is bad.
FLT: Overcurrent Fault Indicator. Open drain output pulls
low when an overcurrent fault has occurred and the circuit
breaker trips. For overcurrent auto-retry tie to UV pin (see
Applications Information for details).
GATE: Gate Drive for External N-Channel FET. An internal
24μA current source charges the gate of the external
N-channel MOSFET. A resistor and capacitor network
from this pin to ground sets the turn-on rate. During an
undervoltage or overvoltage generated turn-off a 250μA
pull-down current turns the MOSFET off. During a short
circuit or undervoltage lockout, a 170mA pull-down current
source between GATE and SOURCE is activated.
GND: Device Ground.
I
this pin is defi ned as the current sense voltage (between
the SENSE
Placing a 20k resistor from this pin to GND creates a 0V to
2V voltage swing when the current sense voltage ranges
from 0mV to 15mV.
INTV
must have a 0.1μF or larger capacitor.
I
threshold, open this pin. This pin is driven by a 20k resis-
tor in series with a voltage source. The pin voltage is used
to generate the current limit threshold. The internal 20k
resistor and an external resistor between I
create an attenuator that lowers the current limit value.
NC: No Connection
MON
SET
: Current Limit Adjustment Pin. For 15mV current limit
: Current Monitor Output. The current sourced from
CC
: Internal 3V Supply Decoupling Output. This pin
+
and SENSE
–
pins) multiplied by 6.67μA/mV.
SET
and ground
OV: Overvoltage Comparator Input. Connect this pin to
an external resistive divider from V
(adjustable version). The LTC4218-12 version uses a fi xed
internal divider with optional external adjustment for 12V
operation. Open the pin if the LTC4218-12 thresholds are
desired. If the voltage at this pin rises above 1.235V, an
overvoltage is detected and the switch turns off. Tie to
GND if unused.
PG: Power Good Indicator. Open drain output pulls low
when the FB pin drops below 1.21V indicating the power
is bad.
SENSE
the opposite of V
rent limit circuit controls the GATE pin to limit the sense
voltage between the SENSE
or less depending on the voltage at the FB pin.
SENSE
the V
SOURCE: N-Channel MOSFET Source Connection. Connect
this pin to the source of the external N-channel MOSFET
switch. This pin provides a return for the gate pull-down
circuit. In the LTC4218-12 version, the powergood com-
parator monitors an internal resistive divider between the
SOURCE pin and GND.
TIMER: Timer Input. Connect a capacitor between this pin
and ground to set a 12ms/μF duration for current limit
before the switch is turned off. If the UV pin is toggled
low while the MOSFET switch is off, the switch will turn on
again following a cool down time of 518ms/μF duration.
UV: Undervoltage Comparator Input. Tie high if unused.
Connect this pin to an external resistive divider from V
for the LTC4218 (adjustable version). The LTC4218-12
version drives the UV pin with an internal resistive divider
from V
olds for 12V operation are desired. If the UV pin voltage
falls below 1.15V, an undervoltage is detected and the
switch turns off. Pulling this pin below 0.62V resets the
overcurrent fault and allows the switch to turn back on
(see Applications Information for details). If overcurrent
auto-retry is desired then tie this pin to the FLT pin.
V
threshold of 2.73V.
DD
: Supply Voltage. This pin has an undervoltage lockout
DD
DD
–
+
: Current Sense Minus Input. Connect this pin to
: Current Sense Plus Input. Connect this pin to
side of the current sense resistor.
. Open the pin if the preset LTC4218-12 thresh-
DD
current sense resistor side. The cur-
+
and SENSE
DD
LTC4218
for the LTC4218
–
pins to 15mV
4218fb
7
DD