33813 Datasheet, PDF (26/54 Pages) Freescale Semiconductor, Inc – One Cylinder Small Engine Control IC

5.1.11 KEYSW Input
KEYSW is the input from the vehicle ignition keyswitch. This signal is at V_BAT (12 V) when the key is inserted and turned to the
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 33813 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
mode. When KEYSW signal goes high, it wakes up the IC, turns on the V_PP regulator and a Power On Reset signal is generated.
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 33813, 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 33813 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
is at V_BAT (12 V) level the BATSW output is a logic 1 (5.0 V), and when KEYSW is at ground (0 V) level, BATSW is at a logic 0.
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 33813, 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.
If the BATSW output is used to control an LED, the LED cathode should be tied to ground and the LED anode should be
connected to the BATSW pin through an external resistor. The value of the external resistor should be 340 ohms or greater. Care
must be taken if the BATSW output is sent off-board due to the chance of shorts to the battery or shorts to ground, for which the
output is not protected. At a minimum, this output should be protected by a diode, the current limit resistor, and an ESD capacitor
(0.01 µF ceramic).
5.1.14 Using ROUT2 as a Power Relay
The ROUT2 (Relay 2 Output) can be used to drive a power relay. The RIN2 input or the RIN2 bit in the SPI Control register can
be used to turn the ROUT2 output on or off as desired. The BATSW output can be connected to the RIN2 input to control the
power relay, or the MCU can chose to control the RIN2 bit in the SPI Control register to actuate the power relay.
The ROUT2 output is unique in that it can be kept turned on even after KEYSW is turned off (as long as the PWREN bit is still
set to a one) by setting the shut down disable (SDD) bit in the ROUT2 Configuration register.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33813
26