LTC4282 datasheet(8/32 Pages) AD

8 / 32 page

LTC4238

Rev. 0

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TMR: Current Limit Timer or SOA Timer Output. The mode

of operation is set by the state of CONFIG pins. In current

limit timer mode, connect a capacitor between this pin

and ground to set a 128ms/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 150s/µF, result-

ing in a 0.08% duty cycle. In SOA timer mode, connect

a RC network between this pin and ground. The current

charging the RC network is proportional to the power

dissipation in the powerpath, which is equal to ΔVSENSE1

multiplied by the voltage difference between the VDD and

SOURCE pins as measured at the VDSFB pin.

TMRFET: FET-Bad Timer Input. Connect a capacitor

between this pin and ground to set a 128ms/µF duration

for a FET-bad condition before the switch is turned off

due to a FET-bad fault. 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 8s/µF, resulting in a 1.6%

duty cycle. Tie to GND if unused.

UV: Undervoltage Comparator Input. Connect this pin

to an external resistive divider from VDD to GND. If the

UV pin falls below 2.2V, an undervoltage is detected and

the switch turns off. Pulling this pin below 1V resets the

overcurrent and FET-bad faults 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. Tie to INTVCC if unused.

VDD: Supply Voltage Input. This pin has an undervoltage

lockout threshold of 6V. VDD is an input for the FET-bad

comparator with a 100mV threshold. It is also an input

for the stress comparator with a 2V threshold.

VDSFB: VDS Foldback Sense Input. This pin is used to

monitor the drain to source voltage of the external

MOSFETs, which is used by the SOA timer to monitor

MOSFET power, as well as set the foldback current limit.

12V systems may connect VDSFB directly to the SOURCE

pin. 48V systems will require an additional RVDSFB resistor

of 10kΩ/V for input voltage over 12V to set the proper

gain of the SOA timer and foldback circuits.

PIN FUNCTIONS

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