Datasheet

LM828
SNOS035D –MARCH 2010–REVISED MAY 2013 www.ti.com
REGULATING V
OUT
It is possible to regulate the negative output of the LM828 by use of a low dropout regulator (such as the
LP2980). The whole converter is depicted in Figure 16. This converter can give a regulated output from −1.8V to
−5.5V by choosing the proper resistor ratio:
V
out
= V
ref
(1 + R
1
/R
2
) (6)
where, V
ref
= 1.23V (7)
Note that the following conditions must be satisfied simultaneously for worst case design:
V
in_min
>V
out_min
+V
drop_max
(LP2980) (8)
+ I
out_max
× R
out_max
(LM828) (9)
V
in_max
< V
out_max
+V
drop_min
(LP2980) (10)
+ I
out_min
× R
out_min
(LM828) (11)
Figure 16. Combining LM828 with LP2980 to Make a Negative Adjustable Regulator
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