A6986 datasheet(24/67 Pages) STMICROELECTRONICS

24 / 67 page

Functional description

A6986

24/67

DocID026211 Rev 6

Figure 12. Output voltage sequencing

High flexibility is achieved thanks to the programmable RST thresholds (see Table 7: LNM /

LCM selection 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.

5.4

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 light-load

when the LCM is active.

5.5

Light-load operation

The MLF pinstrapping during the power-up phase determines the light-load operation (refer

to Table 7: LNM / LCM selection on page 12).

Table 8. Uncompensated error amplifier characteristics

Description

Values

Transconductance

155 µS

Low frequency gain

100 dB

A6986 数据表(PDF) 24 Page - STMicroelectronics