A6985F Datasheet, PDF (24/77 Pages) STMicroelectronics – 38 V 500 mA synchronous step-down switching regulator

Functional description
A6985F
5.3.2
Output voltage sequencing
The A6985F device implements sequencing connecting the RST pin of the master device to
the SS/INH of the slave. The slave is inhibited as long as the master output voltage is
outside regulation so implementing the sequencing (see Figure 12).
Figure 12. Output voltage sequencing
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High flexibility is achieved thanks to the programmable RST thresholds (see Table 7 on
page 11, Table 8 and Table 9 on page 12) and programmable delay time. To minimize the
component count the DELAY pin capacitor can be also omitted so the pin works as a normal
Power Good.
Error amplifier
The voltage error amplifier is the core of the loop regulation. It is a transconductance
operational amplifier whose non inverting input is connected to the internal voltage
reference (0.85 V), while the inverting input (FB) is connected to the external divider or
directly to the output voltage.
Table 10. Uncompensated error amplifier characteristics
Description
Values
Transconductance
155 µS
Low frequency gain
100 dB
The error amplifier output is compared with the inductor current sense information to
perform PWM control. The error amplifier also determines the burst operation at light-load
when the LCM is active.
DocID027738 Rev 2