Analog Integrated Circuit Device Data



Freescale Semiconductor

22

33814

5.1.11 KEYSW Input

ON position. When the key is in the OFF position and/or removed from the keyswitch, this input is pulled to ground by an internal

pull-down resistor. When this signal is low, and the PWREN SPI Control register bit is also low, the 33814 is in the Sleep mode.

If the PWREN SPI control register bit is logic one, when the KEYSW goes low, only the outputs are turned off (except ROUT2 if

the Shut Down Disable bit is set). When the PWREN SPI Control register bit also goes to zero, the entire circuit enters Sleep

This pin is internally protected against a reverse battery condition by an internal diode.

The state of the KEYSW input is also available as a bit in the SPI Status Register.

5.1.12 PWREN SPI Control Register BIT

The PWREN signal is a bit in the SPI Control Register that, along with KEYSW, BATSW, and the ROUT2 output can provide the

power start-up logic of the vehicle.

The purpose of the PWREN signal is allow the MCU to control the shutdown of power to itself when the user turns off the KEYSW.

This may be necessary to allow the MCU the time required to perform its pre-shutdown routines.

When the MCU wants to shutdown the power supplies in the 33814, it must write a logic zero (0) to the PWREN bit in the SPI

Control register. Only the state of the PWREN bit in the SPI Control register will control the shutdown of the 33814 power

supplies.

5.1.13 BATSW Output

The BATSW output pin is a 5.0 V logic level output that by default is an indication of the state of the KEYSW input. When KEYSW

The BATSW output may be used to inform the MCU that the user is trying to shutdown the vehicle.

The BATSW output can also be used to control an LS driver, such as the Relay 2 driver, by connecting the BATSW output to the

RIN2 input.

In certain packaged options of the 33814, the BATSW signal is not brought out to a pin. In this case, the BATSW signal can still

be determined by the MCU by reading the state of BATSW bit in the SPI Status register. The MCU can then control the ROUT2

(Relay 2 output) by setting the “RIN2” bit in the SPI Control register.

If the BATSW signal is not needed by the MCU or to control the Relay 2 output, it can also be configured as a low current LED

high side driver controlled through the SPI interface. As a high side driver, BATSW can also be PWM’d to allow an LED to be

dimmed. A bit in the SPI Battery Switch Logic Output Configuration register called “HSD”, controls whether the BATSW output

will be a simple high side driver, or will be controlled by KEYSW as indicated above.

Figure 7. Recommended Circuit to Use BATSW as an LED Driver

300

Off Board

MC33814

300

BATSW

LED

.01μF

GND