LT1432 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1432' PDF : 28 Pages View PDF
LT1432
U
U
POSITIVE TO EGATIVE CO VERTER
LT1271 operates from a constant 5V supply voltage rather
than the high input voltage.
Output voltage ripple in an inverter can be much higher
than a buck converter because current is delivered to the
output capacitor in high amplitude square waves rather
than a DC level with superimposed tri-wave. C2 is there-
fore somewhat larger than in a buck design. Also C2 must
be rated to handle the large RMS current pulses fed into it.
This RMS current is approximately equal to:
IOUT
VOUT
VIN
For 1A output current, with 5V input, this computes to
1ARMS in the output capacitor. A small additional output
filter would reduce output ripple voltage, but it does not
change the current rating requirement for the main output
capacitor. The reader is referred to a switching regulator
CAD program (SwitcherCAD) supplied by LTC for further
insight into converters. It is suggested that the reader fool
the program by asking for a negative input, positive output
design. It will then select the LT1070 family of ICs which
normally are not used in positive to negative converters.
Efficiency calculations will be somewhat in error at higher
input voltages because the program assumes full input
voltage across the IC. Later versions of SwitcherCAD will
have a special section for this particular design.
100
90
VIN = 20V
80
VIN = 10V
VIN = 5V
70
60
50
0
0.2 0.4 0.6 0.8 1.0
OUTPUT CURRENT (A)
LT1432 F25
Figure 25. Positive-to-Negative Converter Efficiency
26
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