LP2953_15 Datasheet, PDF (20/41 Pages) Texas Instruments – LP295x Adjustable Micropower Low-Dropout Voltage Regulators

LP2952-N, LP2952A, LP2953, LP2953A
SNVS095F – MAY 2004 – REVISED MARCH 2015
Application Information (continued)
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* In shutdown mode, ERROR will go high if it has been pulled up to an external supply. To avoid this invalid
response, pull up to regulator output.
** Exact value depends on dropout voltage. (See Power Supply Recommendations)
Figure 32. ERROR Output Timing
8.1.6 Output Isolation
The regulator output can be left connected to an active voltage source (such as a battery) with the regulator input
power shut off, as long as the regulator ground pin is connected to ground. If the ground pin is left floating,
damage to the regulator can occur if the output is pulled up by an external voltage source. If the regulator input
power (V_IN) is applied, and the SHUTDOWN pin is low, the automatic output discharge circuit will be active, and
any voltage source applied to the output will be discharged to ground.
8.1.7 Reducing Output Noise
In reference applications it may be advantageous to reduce the ac noise present on the output. One method is to
reduce regulator bandwidth by increasing output capacitance. This is relatively inefficient, because large
increases in capacitance are required to get significant improvement.
Noise can be reduced more effectively by a bypass capacitor placed across R1 (see Figure 31). The formula for
selecting the capacitor to be used is:
(2)
This gives a value of about 0.1 μF. When this is used, the output capacitor must be 6.8 μF (or greater) to
maintain stability. The 0.1-μF capacitor reduces the high-frequency gain of the circuit to unity, lowering the output
noise from 260 μV to 80 μV using a 10-Hz to 100-kHz bandwidth. Also, noise is no longer proportional to the
output voltage, so improvements are more pronounced at high output voltages.
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