LP3962EP Datasheet, PDF (12/20 Pages) National Semiconductor (TI) – 1.5A Fast Ultra Low Dropout Linear Regulators

Applications Information (Continued)
internal reference. Increasing the area will decrease the
chance of fitting the die into a smaller package. Increasing
the current drawn by the internal reference increases the
total supply current (ground pin current). Using an optimized
trade-off of ground pin current and die size, LP3962EP/
LP3965EP achieves low noise performance and low quies-
cent current operation.
The total output noise specification for LP3962EP/
LP3965EP is presented in the Electrical Characteristics
table. The Output noise density at different frequencies is
represented by a curve under typical performance charac-
teristics.
SHORT-CIRCUIT PROTECTION
The LP3962and LP3965 is short circuit protected and in the
event of a peak over-current condition, the short-circuit con-
trol 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 LP3962EP/LP3965EP 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 1
shows the relationship between the ERROR 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 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 con-
nected 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 1. Error Flag Operation
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SENSE PIN
In applications where the regulator output is not very close to
the load, LP3965EP can provide better remote load regula-
tion using the SENSE pin. Figure 2 depicts the advantage of
the SENSE option. LP3962EP 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 1.5 A of load current, I_LOAD. The
LP3965EP regulates the voltage at the sense pin. Connect-
ing the sense pin to the remote load will provide regulation at
the remote load, as shown in Figure 2. If the sense option pin
is not required, the sense pin must be connected to the V_OUT
pin.
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