Datasheet

LP3852, LP3855

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SNVS174G –FEBRUARY 2003–REVISED APRIL 2013

SHORT-CIRCUIT PROTECTION

The LP3852 and LP3855 are short circuit protected and in the event of a peak over-current 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 the section

on thermal information for power dissipation calculations.

ERROR FLAG OPERATION

The LP3852/LP3855 produces a logic low signal at the Error Flag pin when the output drops out of regulation

due to low input voltage, current limiting, or thermal limiting. This flag has a built in hysteresis. The timing

diagram in Figure 23 shows the relationship between the ERROR flag and the output voltage. In this example,

the input voltage is changed to demonstrate the functionality of the Error Flag.

The internal Error flag comparator has an open drain output stage. Hence, the ERROR pin should be pulled high

through a pull up resistor. Although the ERROR flag pin can sink current of 1mA, this current is energy drain

from the input supply. Hence, the value of the pull up resistor should be in the range of 10kΩ to 1MΩ. The

ERROR pin must be connected to ground if this function is not used. It should also be noted that when the

shutdown pin is pulled low, the ERROR pin is forced to be invalid for reasons of saving power in shutdown

mode.

Figure 23. Error Flag Operation

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 24 depicts the advantage of the SENSE option. LP3852 regulates the

voltage at the output 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 3.3V output, if the trace resistance is 100mΩ, the

voltage at the remote load will be 3.15V with 1.5A of load current, I

LOAD

. The LP3855 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 24. If the sense option pin is not required, the sense pin must be connected to the V

OUT

pin.

Product Folder Links: LP3852 LP3855