ZLDO285 Ver la hoja de datos (PDF) - Diodes Incorporated.
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ZLDO285 Datasheet PDF : 9 Pages
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ZLDO285
APPLICATIONS
1). Simple 2.85V Supply
+5V In
0V In
IC1
ZLDO285
LBF Spg
SC Gnd
Vin D/C
N/C Vout
C3
100nF
+5V Out
C1
10pF
+2.85V Out
C2
1µF
0V Out
Figure 1
Using a circuit such as Figure 1, the ZLDO285 can
easily provide a 2.85V logic supply from an
available 5V rail where most standard regulators
could not guarantee correct operation. Although
this approach is not particularly energy efficient,
if the load taken at 2.85V is not too large, then the
added complexity and cost of a 2.85V switching
converter may not be justifiable and so this linear
solution can be preferable. This circuit will also
give far less noise than a switching regulator
which can be important when handling low level
analogue signals or low voltage measurements.
2). Post Converter Regulation
A common problem with multiple output switch
mode converters is that only one output can be
used in the feedback control loop of the switching
regulator. Thus only one output is fully regulated.
All other outputs are prone to tracking errors that
occur if the load on any output changes
significantly. By ensuring close coupling of all
transformer windings and minimising the
impedance of all outputs, these errors can be
reduced but never eliminated. A simple way
round this problem is to wind the switching
regulator transformer to give a slightly higher
voltage than required and regulate down from
this to the desired voltage with a linear regulator.
This is indicated in Figure 2. To keep losses low
and so maintain the advantages of a switch
mode supply, it is important that the voltage drop
across this regulator is kept as low as possible,
i.e. just high enough to compensate for the poor
output impedance of the switching power supply
but no higher. The low dropout voltage of the
ZLDO285 allows this circuit technique to be
implemented very effectively, giving a highly
stable and accurate low noise supply.
Voltage
Feedback
D1
+5V Out
TR1
Switching
Regulator
Figure 2
C4
220µF
D2
ZLDO285
LBF Spg
SC Gnd
Vin D/C
N/C Vout
C5
220µF
C1
10pF
+2.85V Out
C2
1µF
0V Out
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