LTC4217 Linear Technology, LTC4217 Datasheet - Page 7

• Manufacturer Part Number: LTC4217
• Description: 2A Integrated Hot Swap Controller
• Manufacturer: Linear Technology

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PIN FUNCTIONS
Exposed Pad: SENSE.
FB: Foldback and Power Good Input. Connect this pin to
an external resistive divider from OUT for the LTC4217
(adjustable) version. The LTC4217-12 version uses a fi xed
internal divider with optional external adjustment. Open
the pin if the LTC4217-12 thresholds for 12V operation are
desired. If the voltage falls below 0.6V the current limit is
reduced using a foldback profi le (see Typical Performance
Characteristics). 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 Internal N-Channel MOSFET. An
internal 24μA current source charges the gate of the
N-channel MOSFET. At start-up the GATE pin ramps up at
a 0.3V/ms rate determined by internal circuitry. During an
undervoltage or overvoltage condition a 250μA pull-down
current turns the MOSFET off. During a short circuit or
undervoltage lockout condition, a 170mA pull-down cur-
rent source between GATE and OUT is activated.
GND: Device Ground.
I
MOSFET switch is divided by 20,000 and sourced from this
pin. Placing a 20k resistor from this pin to GND creates a 0V
to 2V voltage swing when current ranges from 0A to 2A.
INTV
must have a 0.1μF or larger bypass capacitor.
I
open this pin. This pin is driven by a 20k resistor 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
attenuator that lowers the current limit value. In order to
match the temperature variation of the sense resistor, the
voltage on this pin increases at the same rate as the sense
resistance increases. Therefore the voltage at I
proportional to temperature of the MOSFET switch.
OUT: Output of Internal MOSFET Switch. Connect this pin
directly to the load. In the LTC4217-12 version, the PG
MON
SET
: Current Limit Adjustment Pin. For 2A current limit value
: Current Monitor Output. The current in the internal
CC
: Internal 3V Supply Decoupling Output. This pin
SET
and ground create an
SET
pin is
comparator monitors an internal resistive divider between
the OUT pin and GND.
OV: Overvoltage Comparator Input. Connect this pin to an
external resistive divider from V
able) version. The LTC4217-12 version uses a fi xed internal
divider with optional external adjustment for 12V operation.
Open the pin if the LTC4217-12 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. If the FB pin rises above 1.23V and the GATE to OUT
voltage exceeds 4.2V, the open-drain pull-down releases
the PG pin to go high.
SENSE: Current Sense Node and MOSFET Drain. The
current limit circuit controls the GATE pin to limit the
sense voltage between the V
(2A) or less depending on the voltage at the FB pin. The
Exposed Pad on DHC and FE packages are connected to
SENSE and must be soldered to an electrically isolated
printed circuit board trace to properly transfer the heat
out of the package.
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 an cool down time of 518ms/μF duration.
Tie this pin to INTV
and 100ms auto-retry time.
UV: Undervoltage Comparator Input. Tie high if unused.
Connect this pin to an external resistive divider from V
the LTC4217 (adjustable) version. The LTC4217-12 version
drives the UV pin with an internal resistive divider from
V
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 Applica-
tions Information for details). If overcurrent auto-retry is
desired then tie this pin to the FLT pin.
V
has an undervoltage lockout threshold of 2.73V.
DD
DD
. Open the pin if the preset LTC4217-12 thresholds for
: Supply Voltage and Current Sense Input. This pin
CC
for a fi xed 2ms overcurrent delay
DD
DD
and SENSE pins to 15mV
for the LTC4217 (adjust-
LTC4217
DD
4217fb
7
for