LTC4232 datasheet(9/22 Pages) AD

9 / 22 page

LTC4231

Rev. B

For more information www.analog.com

OPERATION

The LTC4231 is a micropower Hot Swap controller that

controls an external N-channel MOSFET to turn on and

off a supply voltage in a controlled manner. This allows a

circuit to be safely inserted and removed from a powered

connector without glitches or connector damage from

uncontrolled inrush current.

When the LTC4231 is first powered up, the gate of the

MOSFET is held at GND to keep it off. Pulling SHDN

high and IN above undervoltage lockout (UVLO) starts

an internal clock that monitors the resistive divider at IN

once every 10ms by connecting GNDSW to GND. A 40ms

debounce cycle is also started. Average ICC during this

debounce mode is 4µA.

After the 40ms debounce cycle, the LTC4231 goes into

start-up mode to ramp up GATE. In this mode, all circuits

blocks except the overvoltage or undervoltage (OV/UV)

block are activated and ICC = 300µA. The internal charge

pump supplies a 10µA pull-up current to GATE. Once

∆VGATE exceeds ∆VGATE(H), STATUS goes high impedance.

This indicates that GATE is high and the power path is on.

Average ICC drops to 4µA during this normal on mode as

some circuit blocks are shut down and the internal charge

pump periodically turns on to recharge GATE as needed.

The periodic monitoring of the IN resistive divider contin-

ues as long as SHDN is high and IN ≥ 2.3V.

If an OV/UV violation is detected during the IN monitor-

ing time, the part goes into voltage fault mode (average

ICC = 4µA) where GATE and STATUS is pulled to GND.

The debounce cycle restarts when no OV/UV violation

is detected during a subsequent IN monitoring window.

The LTC4231 has a circuit breaker comparator that moni-

tors the voltage across the current sense resistor. This

comparator trips when ∆VSENSE exceeds 50mV, bring-

ing the LTC4231 into overcurrent mode. In this mode, all

circuits blocks except the OV/UV block are activated and

ICC = 300µA. If ∆VSENSE > 80mV, the analog current limit

amplifier limits ∆VSENSE to 80mV by servoing ∆VGATE in

an active control loop. The TIMER capacitor is ramped up

with a 50µA pull-up when ∆VSENSE > 50mV. When TIMER

> 1.193V, the current fault latch is set, causing GATE and

STATUS to pull low. The part goes into current fault mode.

In current fault mode, the latchoff (LTC4231-1) version

keeps TIMER and GATE low. The auto-retry (LTC4231-2)

version waits 500ms before GATE is ramped up again.

For both versions, the part can be reset by cycling SHDN

low then high or by cycling IN to GND and back. After the

reset, the LTC4231 goes through a debounce cycle before

re-starting GATE.

SHDN acts as a shutdown switch for the supply path.

When it goes high, the LTC4231 ramps GATE up after a

debounce cycle to turn on the external MOSFET. When it

goes low, GATE is pulled to GND to turn off the external

MOSFET. The LTC4231 then goes into shutdown mode

where ICC drops to 0.3µA.

IN, SENSE, GATE and SOURCE are protected against

reverse inputs of up to –40V. Two reverse voltage com-

parators detect negative input potentials at SENSE or

GATE and quickly connect GATE to SENSE. When used

with back-to-back MOSFETs as shown in Figure 5, this

feature will isolate the load from a negative input.

LTC4232 Datasheet(PDF) 9 Page - Analog Devices

LTC4232 Datasheet(HTML) 9 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Datasheet Download

Link URL