L6985F datasheet(22/65 Pages) STMICROELECTRONICS

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Functional description

L6985F

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DocID027836 Rev 2

4.3.2

Output voltage sequencing

The L6985F 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 of the regulation so implementing the sequencing (see Figure 12).

Figure 12. Output voltage sequencing

High flexibility is achieved thanks to the programmable RST thresholds (see Table 7 on

page 11) 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.

4.4

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.

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 the light-

load when the LCM is active.

Table 8. Uncompensated error amplifier characteristics

Description

Values

Transconductance

155 µS

Low frequency gain

100 dB

L6985F Datasheet(PDF) 22 Page - STMicroelectronics