33989 datasheet(49/66 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33989

TYPICAL APPLICATIONS

SUPPLEMENTAL APPLICATION NOTES

CAN LOW POWER MODE AND WAKE UP

Low Power Mode

In low power mode the CAN is internally supplied from the

VSUP pin. The voltage at V2 pin can be either at 5 V or turned

off. The current sourced from V2, when the CAN is in sleep

mode, is extremely low. In most case the V2 voltage is off,

however the CAN can be set into sleep mode even with 5 V

applied on V2.

In low power mode the CANH and CANL driver are

disabled, and the receiver is also disabled. CANH and CANL

have a typical 50 k ohm impedance to gnd. The wake-up

receiver can be activated if wake-up is enable by an SPI

command.

When the device is set back into TX RX mode by an SPI

command, CANH and CANL are set back into the recessive

level. This is illustrated in Figure 39.

Figure 39. Low Power Mode

Wake-Up

When the CAN interface is in sleep mode with wake up

enabled, the CAN bus traffic is detected. The wake-up option

has to be enabled prior to setting the CAN in sleep mode. The

CAN bus wake-up is a pattern wake-up.

If the CAN is set into sleep mode with “wake-up disabled”,

bus traffic will not be detected by the MC33989.

CAN Wake-Up Report: From the SBC in Sleep or Stop

Mode

The CAN wake-up reports depend upon the MC33989 low

power mode. If the MC33989 is set into sleep mode (V1 and

V2 off), the CAN wake-up or any wake-up is reported to the

MCU by the V1 turn on, leading to MCU supply turn on and

reset release.

If the SBC is in stop mode (V2 of and V1 active), the CAN

wake-up or any wake-up is reported by a pulse on the INT

output.

CAN Wake-Up Report: From the SBC in Normal or

Standby Mode

If the SBC is in normal or standby mode, and the CAN

interface is in sleep mode with wake-up enabled, the CAN

wake-up will be reported by the bit CANWU in the CAN

In case the SBC uses such configuration, the SBC in

normal mode and CAN sleep mode with wake up enable, it is

recommended to check for the CAN WU bit prior to setting

the MC33989 is sleep or stop mode, in case bus traffic has

occurred while the CAN interface was in sleep mode.

CAN Wake-Up Report in the SPI Registers

After a CAN wake-up, a flag is set in the CAN register. Bit

CAN-WU reports a CAN wake-up event while the SBC was in

sleep, stop, normal or standby mode. This bit is set until the

CAN is set by the SPI command in normal mode and CAN

Pattern Wake-Up

In order to wake-up the CAN interface, the following

criteria must be fulfilled:

• The CAN interface wake-up receiver must receive a

series of 3 consecutive valid dominant pulses, each of

them has to be longer than 500 ns and shorter than

500

µs.

• The distance between 2 pulses must be lower than

500

µs and the three pulse must occur within a time

frame of 1 ms.

CANL

CANH

GND

2.5V

CANL-DOM

CANH-DOM

CANL/CANH-REC

CAN in Normal mode

CAN in Sleep mode

(wake-up enable or disable)

CAN in TX RX mode

(controlled by SPI command)

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