VNF1248F datasheet(40/79 Pages) STMICROELECTRONICS

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Protections

11.1

Battery undervoltage shutdown

The device is able to operate down to VS = 6 V, with the charge pump still active. If the battery supply voltage VS

falls below the programmable undervoltage shutdown threshold, the device enters in battery undervoltage mode.

The current sense diagnostic is not available. The charge pump, the output stage and the bypass switch are off

regardless of the SPI status.

If VS rises above the threshold (VS_USD + VS_USD_hys) the device returns to the last mode.

An undervoltage flag is set in the SPI register when VS < VS_USD, and automatically reset when

VS > VS_USD + VS_USD_hys.

11.2

Device overtemperature shutdown

The device temperature is internally monitored. An overtemperature shut-down of the device occurs when TJ

exceeds TTSD. The charge pump, the output stage and the bypass switch are off. A fault indication is given via

SPI.

The device restarts when TJ decreases below TTSD - TTSD_HYS.

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

read via SPI.

11.3

External MOSFET overtemperature shutdown

The external MOSFET temperature is monitored through a 10 kΩ NTC thermistor with one terminal connected to

the Drain of the MOSFET, in order to allow optimal component placement.

RNTC is part of a VBG (VBG= (VsenseN - VNTC_M); typ. 1.2 V) voltage divider through NTC and NTC_M pins:

VNTC= VBG×RNTC

RT_REF+RNTC

(1)

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

read via SPI.

An overtemperature shutdown of the MOSFET occurs when VNTC voltage decreases under a preset threshold,

see Table 20. The threshold can be set via SPI in the range from 100 °C to 150 °C in steps of 5 °C. In this case

both output stages and bypass switch are turned off.

The MOSFET and the bypass switch are re-armed via SPI by clearing latched fault NTC_OVT bit.

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

11.4

External MOSFET desaturation shutdown

The external MOSFET drain-source voltage is monitored by the control IC. A desaturation shutdown of the

MOSFET occurs when the VDS 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 0.3 V to 1.80 V in steps of 50 mV (default = 300 mV),

see Table 17.

The MOSFET and bypass switch are re-armed via SPI by clearing latched fault VDS_MAX bit.

VDS 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 of external MOSFET in off state.

VNF1248F

Protections

DS14109 - Rev 7

page 40/79

VNF1248F Datasheet(PDF) 40 Page - STMicroelectronics

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