LP2960IMX-33 Datasheet, PDF (12/24 Pages) Texas Instruments – LP2960 Adjustable Micropower 0.5A Low-Dropout Regulators

LP2960
SNVS112C – APRIL 1999 – REVISED APRIL 2013
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OUTPUT ISOLATION
If the LP2960 output is connected to an active voltage source (such as a battery) the regulator input should not
be shorted to ground, as this will cause a large current to flow from the battery into the LP2960 output lead.
If the LP2960 input is left floating with the output connected to a battery, a small current (a few mA) will flow into
the output lead.
The “reverse” current flowing from the battery into the LP2960 output can be prevented by using a blocking diode
between the output and the battery.
REDUCING OUTPUT NOISE
In reference applications it may be desirabIe to reduce the AC noise present on the output. One method is to
reduce regulator bandwidth by increasing output capacitance. This is relatively inefficient, since large increases
in capacitance are required to get significant improvement.
Noise can be reduced more effectively by a bypass capacitor placed across R1 (refer to Basic Application
Circuit).
A 0.1 μF capacitor connected across R1 will reduce the high frequency gain of the circuit to unity, lowering the
RMS output noise voltage from 210 μV to 130 μV (typical) using a 10 Hz–100 kHz bandwidth test measurement.
Also, output noise is no longer proportional to the output voltage, so improvements are more pronounced at
higher output voltages.
IMPORTANT: Since the 0.1 μF capacitor reduces the AC gain of the LP2960 to unity, the output capacitance
must be increased to at least 33 μF to assure regulator stability.
DROPOUT DETECTION COMPARATOR
The dropout detection comparator produces a logic “LOW” on the Error output whenever the LP2960 output
drops out of regulation by more than about 5%. This figure results from the comparator’s built-in offset of 60 mV
divided by the 1.23V reference (refer to Block Diagram).
The “5% below nominal” trip level remains constant regardless of the programmed output voltage. An out-of-
regulation condition can result from low input voltage, current limiting, or thermal limiting.
The figure below gives a timing diagram showing the relationship between the output voltage, the Error output,
and input voltage as the input voltage is ramped up and down to a regulator programmed for 5V output.
*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 Application Hints)
Figure 26. Error Output Timing Diagram
The Error signal becomes low as V_IN exceeds about 1.3V. It goes high at about 5V input, where the output
equals 4.75V. Since the dropout voltage is load dependent, the input voltage trip points will vary with load
current, but the output voltage trip point does not.
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