33902 Datasheet, PDF(15/31 Page) Freescale Semiconductor, Inc – High Speed CAN Interface with Embedded 5.0 V Supply

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33902 Datasheet, PDF (15/31 Pages) Freescale Semiconductor, Inc – High Speed CAN Interface with Embedded 5.0 V Supply

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FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

DEVICE STATE DESCRIPTION

STANDBY MODE

Standby mode is a reduced current consumption mode.

CANH and CANL lines are terminated to GND, the SPLIT pin

is high-impedance. In order to monitor bus activities, the CAN

wake-up receiver is ON, INH output remains ON. The voltage

on VIO should be maintained.

The VDD regulator is ON with limited current capability, in

order to maintain the capacitor at VDD charged and allow a

fast transition to Normal mode and fast CAN communication.

Wake-up events occurring on the CAN bus or on the

WAKE pin are reported by a low level of the ERR and RXD

pins. The Standby mode is also the first mode entered after a

device power up. In this case, the VDD regulator is activated

to charge the VDD capacitor, and then the regulator enters the

reduced current capability mode, in order to optimize and

reduce system current consumption. Depending upon the

VDD capacitor âs Equivalent Series Resistance (ESR), a

voltage drop can be observed. See Figure 10.

VDD low (4.25 V)

device start-up

EN, STBY

VE = esr x VDD current limitation

Main VDD

wake-up event detected

Main regulator OFF

Weak regulator ON

Main VDD

Sleep

Standby

Normal

Figure 10. VDD Regulator Start-up

NORMAL MODE

In Normal mode, both the CAN driver and receiver are ON.

In this mode, the CAN bus is controlled by the TXD pin level,

and the CAN bus state is reported on the RXD pin.

The VDD regulator is ON. It supplies the CAN driver and

receiver.The SPLIT pin is active and a 2.5 V biasing is

provided on the SPLIT output pin.

In Normal mode, the ERR pin reports the wake-up source

and the bus failure, after 4 TXD pulses. Normal mode is

entered by setting the EN and STBY pins high. Entering

Normal mode will clear the BATFAIL flag.

Analog Integrated Circuit Device Data

Freescale Semiconductor

LISTEN ONLY MODE

This mode is used to disable the CAN driver, but leave the

CAN receiver active. In this mode, the device is only able to

report the CAN state on the RXD pin. The TXD pin has no

effect on CAN bus lines. This mode is entered by setting the

EN and STBY pins to [0, 1].

In this mode, coming from Normal mode, the ERR pin

reports local failures occurring on the TXD and RXD pins, and

VDD low. When this mode is entered from the Standby mode,

the ERR pin reports the BATFAIL flag.

The VDD regulator is ON. The SPLIT pin is active and a

2.5 V biasing is provided on the SPLIT output pin.

GO TO SLEEP MODE

Go to sleep is an intermediate mode to ultimately set the

device in Sleep mode. The go to sleep is entered by setting

the EN and STBY pins to [1, 0]. If the EN and STBY pins are

maintained to [1,0] for a time longer than tH, the Sleep mode

is automatically entered. In go to Sleep mode, the VDD

regulator remains in its previous state and the SPLIT pin is

deactivated. INH is active.

SLEEP MODE

The Sleep mode is a low power mode. It is entered from

the Go To Sleep mode by setting the EN and STBY pins to [1

0], and automatically from Go To Sleep mode after tH. In

Sleep mode, the VDD regulator is turned off and the SPLIT

pin is deactivated, INH is high-impedance.

In Sleep mode and Go To Sleep mode, the device is able

to wake-up on CAN bus activity or transitions on the WAKE

pin. A wake-up from Sleep mode will set the device in

Standby mode. Sleep mode is also automatically reached if

the voltage at VIO is below the VIOTH for more time than

TVIO-SLP.

DEVICE MAIN FLAGS DESCRIPTION:

This section describes the flags available when the device

is controlled via the EN and STBY pins in a static manner (no

P_SPI control). Additional information and control are

possible using the Pseudo SPI (refer to Extended device

operation).

BATFAIL

This flag is set to signal that the voltage on the VSUP pin

has dropped below VBFTHS, particularly after the device was

disconnected from the battery. In Listen Only mode, the

BATFAIL flag will be available on the ERR pin, coming from

standby, Go To Sleep and Sleep modes. When VSUP is

below VBF threshold, all internal flags and registers are reset

to their initial condition.

CAN Bus Wake-up (WU)

From Standby or Sleep mode, this flag is set if a correct

pattern has been received on the CAN bus. This wake-up is

reported on ERR and RXD pins by a low level in Standby

mode, as well as in Sleep mode if VIO is present.

33902

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