Datasheet

LP3961, LP3964
SNVS056H –MAY 2000–REVISED APRIL 2013 www.ti.com
SENSE PIN
In applications where the regulator output is not very close to the load, LP3964 can provide better remote load
regulation using the SENSE pin. Figure 23 depicts the advantage of the SENSE option. LP3961 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 3.22V with 800mAmps of load current, I
LOAD
. The LP3964 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 23. If the sense option pin is not required, the sense pin must be connected to the V
OUT
pin.
Figure 23. Improving remote load regulation using LP3964
SHUTDOWN OPERATION
A CMOS Logic level signal at the shutdown ( SD) pin will turn-off the regulator. Pin SD must be actively
terminated through a 10kΩ pull-up 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 pull-up resistor is not required. This pin must be
tied to Vin if not used.
DROPOUT VOLTAGE
The dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within
2% of the output voltage. The LP3961/LP3964 use an internal MOSFET with an Rds(on) of 240mΩ (typically).
For CMOS LDOs, the dropout voltage is the product of the load current and the Rds(on) of the internal MOSFET.
REVERSE CURRENT PATH
The internal MOSFET in LP3961and LP3964 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
200mA continuous and 1A peak.
MAXIMUM OUTPUT CURRENT CAPABILITY
LP3961 and LP3964 can deliver a continuous current of 800mA over the full operating temperature range. A
heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of
the application. Under all possible conditions, the junction temperature must be within the range specified under
operating conditions. The total power dissipation of the device is given by:
P
D
= (V
IN
−V
OUT
)I
OUT
+ (V
IN
)I
GND
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