NCV7340 查看數據表（PDF） - ON Semiconductor

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NCV7340

High Speed Low Power CAN Transceiver

ON Semiconductor 

NCV7340

FUNCTIONAL DESCRIPTION

Operating Modes

NCV7340 provides two modes of operation as illustrated

in Table 3. These modes are selectable through pin STB.

Table 3. OPERATING MODES

Pin

STB

Mode

Low

Pin RXD

High

Low

Normal Bus dominant

Bus recessive

High

Standby Wakeup request

detected

No wakeup

request detected

Normal Mode

In the normal mode, the transceiver is able to

communicate via the bus lines. The signals are transmitted

and received to the CAN controller via the pins TxD and

RxD. The slopes on the bus lines outputs are optimized to

give extremely low EME.

Standby Mode

In standby mode both the transmitter and receiver are

disabled and a very low−power differential receiver

monitors the bus lines for CAN bus activity. The bus lines

are terminated to ground and supply current is reduced to a

minimum, typically 10 mA. When a wake−up request is

detected by the low−power differential receiver, the signal

is first filtered and then verified as a valid wake signal after

a time period of tdbus, the RxD pin is driven low by the

transceiver to inform the controller of the wake−up request.

Split Circuit

The VSPLIT pin is operational only in normal mode. In

standby mode this pin is floating. The VSPLIT can be

connected as shown in Figure 2 or, if it’s not used, can be left

floating. Its purpose is to provide a stabilized DC voltage of

0.5 x VCC to the bus avoiding possible steps in the

common−mode signal therefore reducing EME. These

unwanted steps could be caused by an un−powered node on

the network with excessive leakage current from the bus that

shifts the recessive voltage from its nominal 0.5 x VCC

voltage.

Wakeup

When a valid wakeup (dominant state longer than tdbus) is

received during the standby mode the RxD pin is driven low.

The wakeup detection is not latched: RxD returns to High

state after tdbus when the bus signal is released back to

recessive – see Figure 4. Wake−up behavior in case of a

permanent dominant − due to, for example, a bus short −

represents the only difference between the circuit functional

sub−versions listed in the Ordering Information table. When

the standby mode is entered while a dominant is present on

the bus, the “unconditioned bus wake−up” versions will

signal a bus−wakeup immediately after the state transition

(signal RxD1 in Figure 4). The other version will signal

bus−wakeup only after the initial dominant is released

(signal RxD2 in Figure 4). In this way it’s ensured, that a

CAN bus can be put to a low−power mode even if the nodes

have a level sensitivity to RxD pin and a permanent

dominant is present on the bus.

CANH

CANL

STB

RxD 1

RxD 2

PD20100520.01

tdbus

tdbus

normal

standby

time

Figure 4. NCV7340 Wakeup Behavior

Overtemperature Detection

A thermal protection circuit protects the IC from damage

by switching off the transmitter if the junction temperature

exceeds a value of approximately 160°C. Because the

transmitter dissipates most of the power, the power

dissipation and temperature of the IC is reduced. All other

IC functions continue to operate. The transmitter off−state

resets when the temperature decreases below the shutdown

threshold and pin TxD goes high. The thermal protection

circuit is particularly needed when a bus line short circuits.

TxD Dominant Time−out Function

A TxD dominant time−out timer circuit prevents the bus

lines being driven to a permanent dominant state (blocking

all network communication) if pin TxD is forced

permanently low by a hardware and/or software application

failure. The timer is triggered by a negative edge on pin TxD.

If the duration of the low−level on pin TxD exceeds the

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