Low-Power Modes

The transceiver provides three low-power modes that can

be entered or exited through pins STB and EN (Table 3).

Sleep Mode

The sleep mode is the mode with the lowest power con-

sumption. INH is switched to high impedance for deacti-

vation of the external voltage regulator. CANL is biased

to the battery voltage through RTL. If the supply voltage

is provided, RXD and ERR signal the wake-up interrupt.

Standby Mode

The standby mode reacts the same as the sleep mode,

but with a HIGH level on INH. Standby mode can be

used when the external voltage regulator needs to be

kept active during low-power operation.

Power-On Standby Mode

The power-on standby mode behaves similarly to the

standby mode with the battery power-on flag of the

wake-up interrupt signal on ERR. This mode is only for

reading the power-on flag. INH can be high or low in

the power-on standby mode. When the device goes

from standby mode to power-on standby mode, INH is

HIGH. When the device goes from sleep mode to

power-on standby mode, INH is low.

Wake-Up

Wake-up requests are recognized by the transceiver

when a dominant signal is detected on either bus line

or if WAKE detects a pulse for more than 38µs. On a

wake-up request, INH is set high to activate an external

voltage regulator.

the ERR or RXD outputs.

To prevent false wake-up due to transients or RF fields,

the wake-up voltage levels have to be maintained for more

than 38µs. In the low-power modes, the failure detection

circuit remains partly active to prevent increased power

consumption in the event of failures 3, 4, 7, and 8.

Applications Information

The MAX3054/MAX3055/MAX3056 are capable of sus-

taining a network of up to 32 transceivers on a single

bus. The fault-tolerant transceivers are designed to

operate at a total termination resistance of 100

Ω. Both

CANH and CANL lines are terminated with 100

Ω. Since

the total termination resistance of the system is distrib-

uted over the entire bus, each of the transceivers con-

tributes only part of the total 100

Ω termination. The

values of the termination resistors RTL and RTH vary

according to the size of the system and need to be cal-

culated. It is not required that each transceiver be ter-

minated with the same value, the total termination need

only be a total 100

Ω.

The minimum termination resistor value allowed for

each transceiver is 500

Ω, due to the driving capability

of RTH and RTL. This makes it impossible to achieve a

total termination resistance of 100

Ω for systems smaller

than five transceivers. Typically this does not create a

problem because smaller systems usually have shorter

bus cables and have no problem with higher total ter-

mination resistance.

To reduce EMI in the case of an interrupted bus wire it

is recommended not to exceed 6k

Ω termination resis-

tance at a single transceiver even though a higher

value is specified.

±80V Fault-Protected/Tolerant CAN

Transceivers for In-Car Applications

16

______________________________________________________________________________________

Note 1: In case the go-to-sleep command was used before.

Note 3: Wake-up interrupts are released when entering the normal operating mode.

ERR

RXD

MODE

STB

EN

LOW

HIGH

LOW

HIGH

RTL

SWITCHED TO

Go-to-Sleep

Command

01

Sleep

0

0 (Note 1)

Standby

0

0

Wake-up

interrupt signal

(Notes 2 and 3)

—

Wake-up

interrupt signal

(Notes 2 and 3)

—

Power-On

Standby

10

flag

—

Wake-up

interrupt signal

(Notes 2 and 3)

—

Normal

Operating

1

1

Error flag

No error flag

Dominant

received data

Recessive

received data

Table 3. Low-Power Modes