LTC4211 datasheet(10/22 Pages) LINER

10 / 22 page

LTC4235

4235f

For more information www.linear.com/LTC4235

operaTion

The LTC4235 functions as an input supply diode-OR with

inrush current limiting and overcurrent protection by

controlling the external N-channel MOSFETs (MD1, MD2

and MH) on a supply path. This allows boards to be safely

insertedandremovedinsystemswithabackplanepowered

byredundantsupplies.TheLTC4235hasasingleHotSwap

controller and two separate ideal diode controllers, each

providing independent control for the two input supplies.

When the LTC4235 is first powered up, the gates of the

external MOSFETs are held low, keeping them off. As the

DGATE2pull-upcanbedisabledbytheD2OFFpin,DGATE2

will pull high only when the D2OFF pin is pulled low. The

gate drive amplifier (GD1, GD2) monitors the voltage be-

tween the IN and SENSE+ pins and drives the respective

DGATE pin. The amplifier quickly pulls up the DGATE pin,

turning on the MOSFET for ideal diode control, when it

senses a large forward voltage drop. With the ideal diode

MOSFETs acting as input supply diode-OR, the SENSE+

pin voltage rises to the highest of the supplies at the IN1

and IN2 pins. An external capacitor connected at the CPO

pin provides the charge needed to quickly turn on the ideal

diode MOSFET. An internal charge pump charges up this

capacitor at device power-up. The DGATE pin sources

current from the CPO pin and sinks current into the IN

and GND pins.

Pulling the ON pin high and EN pin low initiates a 100ms

debounce timing cycle. After this timing cycle, a 10µA cur-

rent source from the charge pump ramps up the HGATE

pin. When the Hot Swap MOSFET turns on, the inrush

current is limited at a level set by an external sense resistor

(RS) connected between the SENSE+ and SENSE– pins.

An active current limit amplifier (CL) servos the gate of

the MOSFET to 25mV or less across the current sense

resistor depending on the voltage at the OUT pin. Inrush

current can be further reduced, if desired, by adding a

capacitor from HGATE to GND. When OUT voltage rises

above 10.5V and the MOSFET’s gate drive (HGATE to OUT

voltage) exceeds 4.2V, the PWRGD pin pulls low.

The high side current sense amplifier (CM) provides ac-

curate monitoring of current through the current sense

resistor. The sense voltage is amplified by 100 times and

level shifted from the positive rail to a ground-referred

output at the IMON pin. The output signal is analog and

may be used as is or measured with an ADC.

When the ideal diode MOSFET is turned on, the gate drive

amplifier controls DGATE to servo the forward voltage

drop (VIN – VSENSE+) across the MOSFET to 15mV. If the

load current causes more than 15mV of voltage drop,

the gate voltage rises to enhance the MOSFET. For large

output currents, the MOSFET’s gate is driven fully on and

the voltage drop is equal to ILOAD•RDS(ON) of the MOSFET.

In the case of an input supply short-circuit when the

MOSFETs are conducting, a large reverse current starts

flowing from the load towards the input. The gate drive

amplifier detects this failure condition and turns off the

ideal diode MOSFET by pulling down the DGATE pin.

In the case where an overcurrent fault occurs on the sup-

ply output, the current is limited with foldback. After a

delay set by 100µA charging the FTMR pin capacitor, the

fault timer expires and pulls the HGATE pin low, turning

off the Hot Swap MOSFET. The FAULT pin is also latched

low. At this point, the DGATE pin continues to pull high

and keeps the ideal diode MOSFET on.

Internal clamps limit both the DGATE to IN and CPO to IN

voltages to 12V. The same clamp also limits the DGATE

and CPO pins to a diode voltage below the IN pin. Another

internal clamp limits the HGATE to OUT voltage to 12V

and also clamps the HGATE pin to a diode voltage below

the OUT pin.

Power to the LTC4235 is supplied from either the IN or

OUT pins, through an internal diode-OR circuit to a low

dropout regulator (LDO). That LDO generates a 5V supply

at the INTVCC pin and powers the LTC4235’s internal low

voltage circuitry.

LTC4211 Datasheet(PDF) 10 Page - Linear Technology

LTC4211 Datasheet(HTML) 10 Page - Linear Technology

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