LP3871, LP3874

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SNVS225H – FEBRUARY 2003 – REVISED JUNE 2015

Feature Description (continued)

7.3.2 Short-Circuit Protection

The LP3871and LP3874 devices are short-circuit protected and, in the event of a peak overcurrent condition, the

short-circuit control loop will rapidly drive the output PMOS pass element off. Once the power pass element shuts

down, the control loop will rapidly cycle the output on and off until the average power dissipation causes the

thermal shutdown circuit to respond to servo the on/off cycling to a lower frequency.

7.3.3 Low Dropout Voltage

The LP3871 and LP3874 devices feature an ultra-low-dropout voltage, typically 24 mV at 80-mA load current and

240 mV at 0.8-A load current.

The dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within

2% of the nominal output voltage. For CMOS LDOs, the dropout voltage is the product of the load current and

the Rds(on) of the internal MOSFET.

7.3.4 SENSE Pin

In applications where the regulator output is not very close to the load, LP3874 can provide better remote load

regulation using the SENSE pin. Figure 9 depicts the advantage of the SENSE option. LP3871 regulates the

voltage at the OUT pin. Hence, the voltage at the remote load will be the regulator output voltage minus the drop

across the trace resistance. For example, in the case of a 3.3-V output, if the trace resistance is 100 m

Ω, the

voltage at the remote load will be 3.22 V with 0.8 A of load current, ILOAD. The LP3874 regulates the voltage at

the SENSE pin. Connecting the SENSE pin to the remote load will provide regulation at the remote load, as

shown in Figure 9. If the SENSE option pin is not required, the SENSE pin must be connected to the OUT pin.

Figure 9. Improving Remote Load Regulation using LP3874

7.4 Device Functional Modes

7.4.1 Shutdown Mode

A CMOS logic low level signal at the shutdown (SD) pin will turn off the regulator. The SD pin must be actively

terminated through a 10-k

Ω pullup resistor for a proper operation. If this pin is driven from a source that actively

pulls high and low (such as a CMOS rail-to-rail comparator), the pullup resistor is not required. This pin must be

tied to VIN if not used.

7.4.2 Active Mode

When voltage at SD pin of the LP3871 and LP3874 devices is at logic high level, the device is in normal mode of

operation.

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Product Folder Links: LP3871 LP3874