VNF1248F datasheet(28/79 Pages) STMICROELECTRONICS

28 / 79 page

Bypass control management

Bypass switch control and status is determined by the following device settings:

•

BYPASSCTL (CR#1): dedicated programmable control bit in RAM register map.

•

BYPASS_CTL_DEF: bit belonging to NVM default configuration, available if NVM_DEF_CFG_EN is set to

‘1’ (see Section 10.1: NVM – Programmable default configuration), used to define bypass status in standby

and fail-safe states.

•

BYPASS_SAT: bypass switch dedicated protection.

•

FS_MODE (CR#1): fail-safe programmable output behavior.

•

DIN: in fail-safe state, with DIN-controlled configuration (FS_MODE = ’0x’) and BYPASS_CTL_DEF = ‘1’,

first falling edge of DIN will cause bypass turn-off too; this to let DIN having full control on external FET and

avoiding automatic turn-on due BYPASS_SAT protection intervention (that would occur if bypass is kept

on).

The Table 26 provides bypass switch behavior, according to aforementioned setting and correspondent device

states:

Table 26. Bypass switch control vs FSM

To state →

Locked

Fail-safe

Self-test

Power-on

Standby

Unlocked

From state ↓

Power

‑on

Not allowed

OFF

If NVM_DEF_CFG_EN = ‘0’

→ OFF

If NVM_DEF_CFG_EN = ‘1’

→ BYPASS_DEF

Not allowed

Standby

if BYPASS_SAT = '1' → OFF

if FS_MODE = '11' → OFF

if FS_MODE = '10' → HOLD LAST STATE

if FS_MODE = '0x'

→ OFF if NVM_DEF_CFG_EN = '0'

→ BYPASS_CTL_DEF if NVM_DEF_CFG_EN = '1'

If NVM_DEF_CFG_EN = ‘0’

→ BYPASS_CTL

If NVM_DEF_CFG_EN = ‘1’

→ BYPASS_DEF

BYPASS_CTL

Fail-safe

if BYPASS_SAT = '1' → OFF

if FS_MODE = '11' → OFF

if FS_MODE = '10' → HOLD LAST STATE

if FS_MODE = '0x'

→ OFF if NVM_DEF_CFG_EN = '0'

→ BYPASS_CTL_DEF if NVM_DEF_CFG_EN = '1'

→ OFF if DIN falling edge

Unlocked

BYPASS_CTL

if FS_MODE = '11' → OFF

if FS_MODE = '10' → HOLD LAST STATE

if FS_MODE = '0x'

→ OFF if NVM_DEF_CFG_EN = '0'

→ BYPASS_CTL_DEF if NVM_DEF_CFG_EN = '1'

BYPASS_CTL

If BYPASS_SAT=1

→ OFF

If BYPASS_SAT=0

→ BYPASS_CTL

Locked

if BYPASS_SAT = '1'

→ OFF else BYPASS_CTL

Not allowed

BYPASS_CTL

Self-test

Not allowed

BYPASS_CTL

Not allowed

VNF1248F

Bypass control management

DS14109 - Rev 7

page 28/79

VNF1248F Datasheet(PDF) 28 Page - STMicroelectronics

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