SM74503_15 Datasheet, PDF (6/14 Pages) Texas Instruments – SM74503 800mA Low-Dropout Linear Regulator

SM74503
SNVS722A – NOVEMBER 2011 – REVISED APRIL 2013
APPLICATION NOTE
www.ti.com
EXTERNAL CAPACITORS/STABILITY
Input Bypass Capacitor
An input capacitor is recommended. A 10µF tantalum on the input is a suitable input bypassing for almost all
applications.
Output Capacitor
The output capacitor is critical in maintaining regulator stability, and must meet the required conditions for both
minimum amount of capacitance and ESR (Equivalent Series Resistance). The minimum output capacitance
required by the SM74503 is 10µF, if a tantalum capacitor is used. Any increase of the output capacitance will
merely improve the loop stability and transient response. The ESR of the output capacitor should range between
0.3Ω - 22Ω.
LOAD REGULATION
The SM74503 regulates the voltage that appears between its output and ground pins. In some cases, line
resistances can introduce errors to the voltage across the load. To obtain the best load regulation, a few
precautions are needed.
Figure 10, shows a typical application using a fixed output regulator. The Rt1 and Rt2 are the line resistances. It
is obvious that the V_LOAD is less than the V_OUT by the sum of the voltage drops along the line resistances. In this
case, the load regulation seen at the R_LOAD would be degraded from the data sheet specification. To improve
this, the load should be tied directly to the output terminal on the positive side and directly tied to the ground
terminal on the negative side.
Figure 10. Typical Application using Fixed Output Regulator
PROTECTION DIODES
Under normal operation, the SM74503 regulators do not need any protection diode. When a output capacitor is
connected to a regulator and the input is shorted to ground, the output capacitor will discharge into the output of
the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator,
and rate of decrease of V_IN. In the SM74503 regulators, the internal diode between the output and input pins can
withstand microsecond surge currents of 10A to 20A. With an extremely large output capacitor (≥1000 µF), and
with input instantaneously shorted to ground, the regulator could be damaged.
In this case, an external diode is recommended between the output and input pins to protect the regulator, as
shown in Figure 11.
6
Submit Documentation Feedback
Product Folder Links: SM74503
Copyright © 2011–2013, Texas Instruments Incorporated