33813 datasheet(36/54 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

33813

5.3

Functional Device Operation

5.3.1

Power Supply

The 33813 is designed to operate from VPWRMIN to VPWRMAX on the VPWR pin. The VPWR pin supplies power to all internal

regulators, and analog and logic circuit blocks.

5.3.1.1

VPP Pre-regulator

The VPP pre-regulator supplies the input voltage to the VCC 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 VCC and VPROT regulators. The VPPSENS pin is used to

feedback the value of the VPP voltage for regulation. Since the VPP 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

VCC Regulator

The VCC 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 VCC regulator contains an internal pass transistor which is protected against over-current.

5.3.1.3

VPROT Regulator

The protected output VPROT is a tracking regulator uses the VCC output as a reference. Since it is expected that the VPROT

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 VPROT supply is enabled at power-on but can be disabled via the SPI control register.

5.3.2

Power ON Reset (POR)

Applying VPWR 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, VPP, VCC, and VPROT, are enabled when KEYSW is brought high.

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