FS6408 datasheet(51/111 Pages) NXP

51 / 111 page

NXP Semiconductors

FS6407/FS6408

6.7.4.2

Voltage monitoring

The overvoltage detection switches OFF the regulator. The regulator remains ON during undervoltage detection. A diagnostic is reported

in the dedicated register, generating an Interrupt, and may bring the application into Fail-safe state depending on the supervisor

configuration (registers INIT SUPERVISOR 1, 2, 3).

6.7.5

VAUX voltage regulator

VAUX is a highly flexible linear voltage regulator which can be used either as an auxiliary supply dedicated to additional device in the ECU

or as a sensor supply. An external PNP transistor must be used (no internal current capability). If VAUX is not used in the application, the

VAUX_E and SELECT pins must be connected to VPRE to not populate the external PNP, as described in Figure 51.

If VAUX is used as an auxiliary supply, the output voltage is selectable between 5.0 V and 3.3 V. Since this voltage rail can be used to

supply MCU IOs, the selection is done with an external resistor connected between the SELECT pin and ground. In such case, the voltage

accuracy is

±3.0% with a maximum output current capability at 300 mA. If VAUX is used as a sensor supply rail, the output voltage is

selectable between 5.0 V and 3.3 V. VCCA can be used as reference for the sensor supply used as tracker. The selection is done during

the INIT phase and secured (bit VAUX_TRK_EN in the register INIT VREG2). The tracking accuracy is ±15 mV.

Figure 35. Example of VAUX used in tracker mode

6.7.5.1

Current limitation

A current limitation is implemented to avoid uncontrolled power dissipation of the external PNP transistor. The current is limited to IAUX_LIM

and the regulator is switch OFF after a dedicated duration TAUX_LIM_OFF under current limitation. A SPI command is needed to restart the

regulator. To limit the power dissipation in the external PNP transistor in case of a short-circuit to GND of the VAUX pin, a current limitation

foldback scheme is implemented to reduce the current limitation to IAUX_LIM_FB when VAUX is below VAUX_LIM_FB.

SW2

FB1

VCCA_E

VCCA_B

Vcca 5V

COMP1

VCORE_SNS

L3 - 2.2 µH

100nF

C10

C11

Vcore

4.7 µF

40µF

PGND

GND

BOOT_CORE

Vcore

Buck – 1.5A

VCCA - LDO1

100/300mA

VAUX - LDO2

300mA

VAUX_E

VAUX_B

Vaux 5V

4.7 µF

GND

PNP2

MCU

VDD_LV_1.2V

V_ADC_5V

Ext

Sensor

ADC_IN

GND

Int 3.3/

5V ref

ECU

limit

V_Peripherals & I/O

Input ref

FS6407/

FS6408

FS6408 Datasheet(PDF) 51 Page - NXP Semiconductors

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