LP3963 Datasheet, PDF (14/25 Pages) National Semiconductor (TI) – 3A Fast Ultra Low Dropout Linear Regulators

LP3963, LP3966
SNVS067H – APRIL 2000 – REVISED APRIL 2013
www.ti.com
SENSE PIN
In applications where the regulator output is not very close to the load, LP3966 can provide better remote load
regulation using the SENSE pin. Figure 22 depicts the advantage of the SENSE option. LP3963 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 3V with 3A of load current, I_LOAD. The LP3966 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 22. If the sense option pin is not required, the sense pin must be connected to the V_OUT pin.
Figure 22. Improving remote load regulation using LP3966
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 nominal output voltage. The LP3963/LP3966 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 LP3963 and LP3966 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.
POWER DISSIPATION/HEATSINKING
LP3963 and LP3966 can deliver a continuous current of 3A 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
where I_GND is the operating ground current of the device (specified under Electrical Characteristics).
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