LP2960IMX-33 Datasheet, PDF (11/24 Pages) Texas Instruments – LP2960 Adjustable Micropower 0.5A Low-Dropout Regulators

LP2960
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APPLICATION HINTS
SNVS112C – APRIL 1999 – REVISED APRIL 2013
EXTERNAL CAPACITORS
Bypass capacitors on the input and output of the LP2960 are required: without these capacitors, the part will
oscillate.
A capacitor (whose value is at least 4.7 μF) must be connected from the V_IN pin to ground. If the input capacitor
is located more than one inch away from the LP2960, the capacitor may have to be increased to 22 μF to assure
stability. A capacitor is also required between V_OUT and Ground, and the minimum amount of capacitance
required here depends on output voltage.
If the output voltage of the LP2960 is set to 5V, a minimum of 10 μF is needed in output capacitance. At 3.3V
output, at least 22 μF is required to assure stability.
ESR LIMIT: The ESR of the capacitor used on the LP2960 must be less than 0.7Ω throughout the entire
operating temperature range to assure stability.
The ESR of an aluminum eIectroIytic capacitor is typically only specified at 25°C, and does not reflect the
maximum ESR that can be expected to occur over the entire temperature range of the capacitor.
Aluminum electrolytics show a marked increase in ESR at low temperatures (ESR can increase by a factor of 30
or more when going from 25°C to −30°C) which could lead to oscillation probIems in applications with very low
ambient temperatures. Solid tantalum capacitors are recommended for use in such cases.
Regulator instability can be caused by stray (board layout) capacitance appearing at the Feedback terminal.
Oscillations from this effect are most Iikely to occur when very high value resistors are used to set the output
voltage.
Adding a 100 pF capacitor between the Output and Feedback pins and increasing the output capacitor to at least
22 μF will stop the osciIIations.
MINIMUM LOAD
The internal resistive divider in the LP2960 provides sufficient output loading for proper regulation. If external
resistors are used to set the LP2960 output voltage, a minimum current of 5 μA through the externaI resistive
divider is recommended.
It should be noted that a minimum load current is specified in several of the test conditions listed under Electrical
Characteristics, and this value of load current must be used to get correlation on these test limits.
PROGRAMMING THE OUTPUT VOLTAGE
The LP2960 regulator may be pin-strapped for operation at the nominal output voltage using its internal resistive
divider by tying the Output and Sense pins together and also tying the Feedback and V_TAP pins together.
Alternatively, it may be programmed for any voltage between the 1.23V reference and the 30V maximum rating
using an external pair of resistors (see Basic Application Circuit).
The complete equation for the output voltage is:
V_OUT = V_REF × (1 + R1/R2) + (I_FB × R1)
(1)
The term V_REF is the 1 .23V reference and I_FB is the Feedback pin bias current (−20 nA typical). The minimum
recommended load current of 5 μA sets an upper limit of 240 kΩ on the value of R2 in cases where the regulator
must work with no load (see Minimum Load).
For best output accuracy, choosing R2 = 100 kΩ will reduce the error resulting from I_FB to 0.17% while increasing
the resistive divider current to 12 μA. Since the typicaI quiescent current of the LP2960 is 450 μA, this added
current through R2 is negligible.
DROPOUT VOLTAGE
The dropout voltage of the regulator is defined as the minimum input-to-output voltage differential required for the
output voltage to stay within 100 mV of the output voltage measured with a 1V differential. The dropout voltage is
independent of the programmed output voltage.
Copyright © 1999–2013, Texas Instruments Incorporated
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