Datasheet

LP38501-ADJ, LP38503-ADJ
SNVS522H –AUGUST 2007–REVISED APRIL 2013 www.ti.com
A solid Tantalum should work better, so the aluminum electrolytic is replaced by a 220 µF Tantalum (Figure 24).
The peak amplitude of the output transient is now reduced to about 130 mV, just slightly worse than the value of
the 47 µF ceramic alone.
Figure 24. 10 µF Ceramic Paralleled By 220 µF Tantalum
The OSCON (ultra low ESR) aluminum electrolytic is the best of the electrolytics. Figure 25 shows the output
voltage transient is reduced down to about 90 mV (about 5% of V
OUT
) when a 220 µF OSCON is added to the 10
µF ceramic. This indicates that some kind of ultra-low ESR aluminum electrolytic used in parallel with some
ceramic capacitance is probably the best approach for extremely fast transients, but each application must be
dialed in for it’s specific load requirements.
Figure 25. 10 µF Ceramic Paralleled By 220 µF OSCON
PRINTED CIRCUIT BOARD LAYOUT
Good layout practices will minimize voltage error and prevent instability which can result from ground loops. The
input and output capacitors should be directly connected to the IC pins with short traces that have no other
current flowing in them (Kelvin connect).
The best way to do this is to place the capacitors very near the IC and make connections directly to the IC pins
via short traces on the top layer of the PCB. The regulator’s ground pin should be connected through vias to the
internal or backside ground plane so that the regulator has a single point ground.
The external resistors which set the output voltage must also be located very near the IC with all connections
directly tied via short traces to the pins of the IC (Kelvin connect). Do not connect the resistive divider to the load
point or DC error will be induced.
RFI/EMI SUSCEPTIBILITY
RFI (Radio Frequency Interference) and EMI (Electro-Magnetic Interference) can degrade any integrated circuit's
performance because of the small dimensions of the geometries inside the device. In applications where circuit
sources are present which generate signals with significant high frequency energy content (> 1 MHz), care must
be taken to ensure that this does not affect the IC regulator.
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