Datasheet
DocID17977 Rev 2 15/46
ST1S14 Additional features and limitations
5.2 Minimum output voltage over V
IN
range
The minimum regulated output voltage at a given input voltage is limited by the minimum
conduction time of the power element, that is 90 nsec typ. for the ST1S14:
Equation 1
which is plotted in Figure 14. The reference of the embedded error amplifier (1.22 V) sets
the minimum V
O_SET
at low V
IN
.
Figure 8. V
O_MIN
over input voltage range
Figure 8 shows the minimum output voltage over input voltage range to have constant
switching activity and a predictable output voltage ripple.
The regulator can, however, regulate the minimum input voltage over the entire input
voltage range but, given the 90 ns minimum conduction time of the power element, it skips
some pulses to keep the output voltage in regulation when Equation 1 is not satisfied.
This operation is not recommended at the nominal input voltage of the application mainly
because it affects the output voltage ripple, but it is generally accepted during a line
transient event.
V
O_MIN
V
IN
()V
IN
D
MIN
⋅ V
IN
T
ON_MIN
T
SW
--------------------- -
⋅ V
IN
90ns
1.18μs
------------------
⋅== =
$09