L6986H datasheet(42/68 Pages) STMICROELECTRONICS

42 / 68 page

Figure 43. Voltage supervisor operation

The comparator monitoring the FB voltage has four different programmable thresholds (80%, 87%, 93%, 96%

nominal output voltage) for high flexibility (see MLF pin, Table 7. LNM/ LCM selection (L6986H3V3),

Table 8. LNM/ LCM selection (L6986H5V), and Table 9. LNM/ LCM selection (L6986H)).

When the RST comparator detects the output voltage is in regulation, a 2 mA internal current source starts to

charge an external capacitor to implement a voltage ramp on the DELAY pin. The RST open collector is then

released as soon as VDELAY = 1.234 V (see Figure 43. Voltage supervisor operation). The CDELAY is dimensioned

as follows:

CDELAY=ISSCH⋅TDELAY

VDELAY =2μA⋅TDELAY

1.234V

(41)

The maximum suggested capacitor value is 270 nF.

The L6986H also activates internal pull-down on RST pin in case overvoltage protection is triggered. As soon as

the output voltage goes below OVP threshold (20% typ.), the 2 µA internal current source starts to charge an

external capacitor to implement a voltage ramp on the DELAY pin. The RST open collector is then released as

soon as VDELAY = 1.234 V(see figure below).

L6986H

Voltage supervisor

DS12905 - Rev 2

page 42/68

L6986H 数据表(PDF) 42 Page - STMicroelectronics