VIPER35 datasheet(36/44 Pages) STMICROELECTRONICS

36 / 44 page

Operation description

VIPer35

36/44

DocID026980 Rev 4

Figure 42. Burst mode timing: light load management

8.15

Brown-out

Brown-out protection is a not-latched shutdown function active when a condition of mains

undervoltage is detected. The brown-out comparator is internally referenced to VBRth

threshold (see Figure 10) and disables the PWM if the voltage applied to BR pin is below

this internal reference. Under this condition the power MOSFET turns off.

Until the brown-out condition is present, the VDD voltage continuously oscillates between

the VDDon and the UVLO thresholds, as shown in the timing diagram of Figure 43. A voltage

hysteresis improves the noise immunity.

The switching operation restarts as the voltage on the pin is above the reference plus the

voltage hysteresis. The brown-out comparator is provided with a current hysteresis, IBRhyst.

The designer has to set the rectified input voltage above which the power MOSFET starts

switching after brown-out event, VINon, and below which the power MOSFET switches off,

VINoff. Thanks to the IBRhyst, see Table 7, these two thresholds can be set separately.

When VINon and VINoff levels are fixed, with reference to Figure 43, the following

relationships can be established to calculate RH and RL resistors:

Equation 12

Equation 13

time

VCOMP

VFBbm

VFBbm +VFBbmhys

IDD1

IDD0

IDD

IDRAIN

ID_BM

Burst mode

GIPG2801151121LM

BRhyst

---------------------

–

INon

INoff

BRhyst

–

INon

BRth

–

---------------------------------------------------------------

BRth

BRhyst

------------------

⋅

INon

INoff

BRhyst

–

BRhyst

---------------------------------------------------------------

BRhyst

---------------------

----------------------------------

⋅

VIPER35 датащи(PDF) 36 Page - STMicroelectronics

VIPER35 датащи(HTML) 36 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

датащи скачать

ссылки URL