LTC4217
7
4217fg
For more information www.linear.com/LTC4217
pin FuncTions
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 fixed
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 profile (see the Typical Perfor-
mance Characteristics section). If the voltage falls below
1.21V, the PG pin will pull low to indicate the power is bad.
F LT : 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
the Applications Information section 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 140mA pull-down cur-
rent source between GATE and OUT is activated.
GND: Device Ground.
I
MON
: Current Monitor Output. The current in the internal
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
CC
: Internal 3.1V Supply Decoupling Output. This pin
must have a 1µF or larger bypass capacitor. Overloading
this pin can disrupt internal operation.
I
SET
: Current Limit Adjustment Pin. For a 2A current limit
value 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 (R
ISET
)) and an external resistor (R
SET
) between
I
SET
and ground create an attenuator that lowers the cur-
rent limit value. Due to circuit tolerance R
SET
should not be
less than 2k. 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
SET
pin is made 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
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
DD
for the LTC4217 (adjust-
able) version. The LTC4217-12 version uses a fixed 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
DD
and SENSE pins to 15mV
(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 a cooldown time of 518ms/µF duration.
Tie this pin to INTV
CC
for a fixed 2ms overcurrent delay
and 100ms auto-retry time.
UV: Undervoltage Comparator Input. Tie high if unused.
Connect this pin to an external resistive divider from V
DD
for the LTC4217 (adjustable) version. The LTC4217-12
version drives the UV pin with an internal resistive divider
from V
DD
. Open the pin if the preset LTC4217-12 thresholds
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 overcur
-
rent fault and allows the switch to turn back on (see the
Applications Information section for details). If overcurrent
auto-retry is desired then tie this pin to the F LT pin.
V
DD
: Supply Voltage and Current Sense Input. This pin
has an undervoltage lockout threshold of 2.73V.
