LTC4232

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For more information www.linear.com/LTC4232

APPLICATIONS INFORMATION

Current Limit Adjustment

The default value of the active current limit is 5.6A. The

current limit threshold can be adjusted lower by placing

the clamp circuit) sets the CS amplifier’s built-in offset

voltage. This offset voltage directly determines the active

efficient reference. This voltage is set to 0.618V at room

temperature which corresponds to a 5.6A current limit at

room temperature.

forms a resistive divider with the internal 20k sourcing

pin and therefore lower the current limit threshold. The

overall current limit threshold precision is reduced to

±12% when using a 20k resistor to halve the threshold.

Using a switch (connected to ground) in series with this

external resistor allows the active current limit to change

only when the switch is closed. This feature can be used

when the start-up current exceeds the typical maximum

load current.

Monitor MOSFET Temperature

shown in the Typical Performance Characteristics section.

provides an indicator of the MOSFET temperature.

There is an overtemperature circuit in the LTC4232 that

When the die temperature exceeds 145°C the circuit turns

off the MOSFET until the temperature drops to 125°C.

Monitor MOSFET Current

The current in the MOSFET passes through a sense resis-

tor. The voltage on the sense resistor is converted to a

current. This output current can be converted to a voltage

using an external resistor to drive a comparator or ADC.

A microcontroller with a built-in comparator can build a

simple integrating single-slope ADC by resetting a capaci-

tor that is charged with this current. When the capacitor

voltage trips the comparator and the capacitor is reset, a

timer is started. The time between resets will indicate the

MOSFET current.

Monitor OV and UV Faults

Protecting the load from an overvoltage condition is the

main function of the OV pin. In Figure 1 an external resis-

tive divider (driving the OV pin) connects to a comparator

the switch will be allowed to turn on immediately. In the

LTC4232 the OV pin threshold is 1.235V when rising, and

1.215V when falling out of overvoltage.

The UV pin functions as an undervoltage protection pin

or as an “ON” pin. In the Figure 1 application the MOSFET

sequently rises above 9.88V for 100ms, the switch will

be allowed to turn on again. The LTC4232 UV turn-on/off

thresholds are 1.235V (rising) and 1.155V (falling).

InthecasesofanundervoltageorovervoltagetheMOSFET

turns off and there is indication on the PG status pin. When

the overvoltage is removed the MOSFET’s gate ramps up

immediately at the rate determined by the INRUSH block.

Figure 4. Short-Circuit Waveform

10V/DIV

2A/DIV

10V/DIV

TIMER

2V/DIV

1ms/DIV

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