SP6203_07 Datasheet, PDF (11/16 Pages) Sipex Corporation – Low Noise, 300mA and 500mA CMOS LDO Regulators

Note that the regulator cannot always be used at
its maximum current rating. For example, in a
5V input to 3.0V output application at an ambi-
ent temperature of 25°C and operating at the full
500mA (I_GND = 0.355mA) load, the regulator is
limited to a much lower load current, deter-
mined by the following equation:
523mW = ( [5V-3V]*[ I_load(max)]) +(5V*0.350mA)
After calculation, we find that in such an appli-
cation (SP6205) the regulator is limited to
260.6mA. Doing the same calculations for the
300mA LDO (SP6203) will limit the regulator’s
output current to 260.9mA.
Also, taking advantage of the very low dropout
voltage characteristics of the SP6203/6205,
power dissipation can be reduced by using the
lowest possible input voltage to minimize the
input-to-output drop.
Adjustable Regulator Applications
The SP6203/6205 can be adjusted to a specific
output voltage by using two external resistors
(see functional diagram). The resistors set the
output voltage based on the following equation:
V_OUT = V_REF *(R1/R2 + 1)
Resistor values are not critical because ADJ
(adjust) has a high input impedance, but for best
performance use resistors of 470K1 or less. A
bypass capacitor from ADJ to V_OUT provides
improved noise performance.
THEORY OF OPERATiON: Continued
Layout Considerations
The primary path of heat conduction out of the
package is via the package leads. Therefore,
careful considerations have to be taken into
account:
1) Attaching the part to a larger copper footprint
will enable better heat transfer from the device,
especially on PCB’s where there are internal
ground and power planes.
2) Place the input, output and bypass capacitors
close to the device for optimal transient re-
sponse and device behavior.
3) Connect all ground connections directly to
the ground plane. In case there’s no ground
plane, connect to a common local ground point
before connecting to board ground.
Such layouts will provide a much better thermal
conductivity (lower e_JA) for, a higher maximum
allowable power dissipation limit.
Dual-Supply Operation
When used in dual supply systems where the
regulator load is returned to a negative supply,
the output voltage must be diode clamped to
ground.
DDaattee:: Ap2r2/-0/705
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