AST1S31HF Datasheet, PDF (10/33 Pages) STMicroelectronics – Internal soft-start and enable

Functional description
AST1S31HF
6.1
Output voltage adjustment
The error amplifier reference voltage is 0.8 V typical. The output voltage is adjusted
according to the following formula (see Figure 1 on page 1):
Equation 1
V_OUT
=
0.8



1
+
R^{-R----12-}
The internal architecture of the device requires a minimum off time, cycle by cycle, for the
output voltage regulation. The minimum off time is typically equal to 66 ns.
The control loop compensates for conversion losses with duty cycle control. Since the
power losses are proportional to the delivered output power, the duty cycle increases with
the load current request.
Figure 4 shows at different loading conditions the maximum regulated output voltage over
the input voltage range.
Figure 4. Maximum output voltage over loading conditions
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