Datasheet

LM2990
SNVS093D –JUNE 1999–REVISED APRIL 2013 www.ti.com
APPLICATION HINTS
EXTERNAL CAPACITORS
The LM2990 regulator requires an output capacitor to maintain stability. The capacitor must be at least 10 μF
aluminum electrolytic or 1 μF solid tantalum. The output capacitor's ESR must be less than 10Ω, or the zero
added to the regulator frequency response by the ESR could reduce the phase margin, creating oscillations
(refer to the graph on the right). An input capacitor, of at least 1 μF solid tantalum or 10 μF aluminum electrolytic,
is also needed if the regulator is situated more than 6″ from the input power supply filter.
FORCING THE OUTPUT POSITIVE
Due to an internal clamp circuit, the LM2990 can withstand positive voltages on its output. If the voltage source
pulling the output positive is DC, the current must be limited to 1.5A. A current over 1.5A fed back into the
LM2990 could damage the device. The LM2990 output can also withstand fast positive voltage transients up to
26V, without any current limiting of the source. However, if the transients have a duration of over 1 ms, the
output should be clamped with a Schottky diode to ground.
Figure 28. Output Capacitor ESR
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