33813 Datasheet, PDF (36/54 Pages) Freescale Semiconductor, Inc – One Cylinder Small Engine Control IC

5.3 Functional Device Operation
5.3.1 Power Supply
The 33813 is designed to operate from VPWR_MIN to VPWR_MAX on the VPWR pin. The VPWR pin supplies power to all internal
regulators, and analog and logic circuit blocks.
5.3.1.1 V_PP Pre-regulator
The V_PP pre-regulator supplies the input voltage to the V_CC and VPROT regulators. It uses an external PNP transistor as a pass
element. This allows the user to choose the PNP’s size and package considerations to meet the system requirements. The
amount of power that the external PNP transistor will have to dissipate depends on the maximum voltage the system can be
expected to run at and the maximum expected current drawn from the V_CC and V_PROT regulators. The VPPSENS pin is used to
feedback the value of the V_PP voltage for regulation. Since the V_PP regulator is not intended to supply off-the-board loads, there
is no short to ground or short to battery protection on the output of the external PNP.
5.3.1.2 V_CC Regulator
The V_CC regulator output is used for supplying 5.0 Volts to the MCU, and for setting communication threshold levels via the
internal SPI SO driver. The V_CC regulator contains an internal pass transistor which is protected against over-current.
5.3.1.3 V_PROT Regulator
The protected output VPROT is a tracking regulator uses the VCC output as a reference. Since it is expected that the V_PROT
regulator will supply 5.0 Volts to external sensors in the vehicle, it is well protected against shorts to battery, shorts to ground and
over-current. The V_PROT supply is enabled at power-on but can be disabled via the SPI control register.
5.3.2 Power ON Reset (POR)
Applying V_PWR and bringing KEYSW high (VBAT) will generate a Power On Reset (POR) and place the device in the Normal
operating state. The Power On Reset circuit incorporates a timer to prevent high frequency transients from causing an erroneous
POR.
Upon enabling the device (KEYSW High), outputs will be activated based on the initial state of the control register or parallel
input. All three supplies, V_PP, V_CC, and V_PROT, are enabled when KEYSW is brought high.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33813
36