VNF1048F datasheet(23/52 Pages) STMICROELECTRONICS

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5.5

Hard short circuit latch-off

The external MOSFET drain-source current is monitored by the Control IC through the current sense amplifier,

which reads the voltage drop across a high side shunt resistor. A hard short circuit shut-down of the MOSFET

occurs when the current sense voltage exceeds the preset threshold. In this case both output stage and bypass

switch are turned off. The threshold can be set via SPI in the range from 20 mV to 160 mV.

The MOSFET is re-armed via SPI by clearing HSHT latched fault bit.

VHSHT is converted by a dedicated ADC converter. The converted result is stored in the Status register and can

be read via SPI.

This protection is not active in case the external MOSFET is in OFF state.

5.6

Current vs time latch-off

The external MOSFET drain-source current is monitored by the Control IC through the current sense amplifier,

which reads the voltage drop across a high side shunt resistor. The overload detection circuitry emulates the

response of a traditional fuse. An overcurrent shut-down of the MOSFET occurs when the current sense voltage

exceeds the preset threshold for longer than the preset time. In this case both output stages and bypass switch

are turned off. The threshold can be set via SPI in the range 6 mV to 90 mV, while the nominal trip time can be

programmed in the range from 1 s to 511 s.

The MOSFET is re-armed via SPI by clearing FUSE_LATCH latched fault bit. This protection is not active in case

the external MOSFET is in OFF state.

In case of hard short protection event occurrence, reported by HSHT flag bit, FUSE_LATCH bit is set as well.

5.7

Low Current Bypass desaturation shut-down

Internal bypass switch VDS voltage (VS - VOUT) is monitored by the IC, to protect the switch from load current

sink changes.

A desaturation shut-down of the bypass occurs when its VDS exceeds a fixed threshold (~1.3V); in this situation,

the bypass switch is turned off while the external FET is turned on through HS_GATE output, directly by

hardware, regardless of their software controlled bit status, in order to protect the bypass and provide the

requested current capability to connected load.

This represents the so-called AUTO-ON event and it is flagged by bit #4 (AUTOON) of the Global Status Byte,

that corresponds to BYPASS_SAT flag of Status Register #1.

Bypass switch can be re-armed through SPI control by clearing BYPASS_SAT fault latched bit.

This protection is not active in case bypass switch is in OFF state.

A particular case is represented by Stand-By wakeup event occurrence, with FSM state transition to Wake-Up

state, due to bypass switch desaturation: only in this situation, in addition to the aforementioned actions on

bypass switch and external FET, the device will signal, by driving DIAG pin low, that it has been woken up by

hardware event (load current increase), in order to allow host control to take proper actions.

It is important to notice that bypass switch cannot be used to charge any type of load, even those requesting

small currents capability: on the contrary, it shall be used to keep powered application loads, previously charged

by external FET, when they switch to low-power consumption modes (i.e. Stand-By).

VNF1048F

Hard short circuit latch-off

DS13084 - Rev 6

page 23/52

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