LP3852, LP3855

SNVS174I – FEBRUARY 2003 – REVISED FEBRUARY 2015

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9.3 Feature Description

9.3.1 SENSE Pin

In applications where the regulator output is not very close to the load, LP3855 can provide better remote load

regulation using the SENSE pin. Figure 16 depicts the advantage of the SENSE option. The LP3852 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,

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

shown in Figure 16. If the SENSE pin is not required, the SENSE pin must be connected to the OUT pin.

Figure 16. Improving Remote Load Regulation Using LP3855

9.3.2 SHUTDOWN (SD) Operation

A CMOS Logic low level signal at the SD pin will turn off the regulator. SD 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

used.

The SD pin threshold has no voltage hysteresis. If the SD pin is actively driven, the voltage transition must rise

and fall cleanly and promptly.

9.3.3 Dropout Voltage

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

9.3.4 Reverse Current Path

The internal MOSFET in LP3852 and LP3855 has an inherent parasitic diode. During normal operation, the input

voltage is higher than the output voltage and the parasitic diode is reverse biased. However, if the output is

pulled above the input in an application, then current flows from the output to the input as the parasitic diode gets

forward biased. The output can be pulled above the input as long as the current in the parasitic diode is limited to

200-mA continuous and 1-A peak.

9.3.5 Short-Circuit Protection

The LP3852 and LP3855 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. Please refer to for power

dissipation calculations.

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