MCP25612FD datasheet(4/26 Pages) MICROCHIP

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MCP25612FD

DS20005409A-page 4

 2015 Microchip Technology Inc.

1.2

Transmitter Function

The CAN bus has two states:

• Dominant state

• Recessive state

A Dominant state occurs when the differential voltage

between CANHx and CANLx is greater than

VDIFFX(D)(I). A Recessive state occurs when the differ-

ential voltage is less than VDIFFX(R)(I). The Dominant

and Recessive states correspond to the Low and High

state of the TXDX input pin, respectively. However, a

Dominant state initiated by another CAN node will

override a Recessive state on the CAN bus.

1.3

Receiver Function

In Normal mode, the RXDX output pin reflects the

differential bus voltage between CANHx and CANLx.

The Low and High states of the RXDX output pin

correspond to the Dominant and Recessive states of

the CAN bus, respectively.

1.4

Internal Protection

CANHx and CANLx are protected against battery short

circuits and electrical transients that can occur on the

CAN bus. This feature prevents destruction of the

transmitter output stage during such a Fault condition.

The device is further protected from excessive current

loading by thermal shutdown circuitry that disables the

output drivers when the junction temperature exceeds

a nominal limit of +175°C. All other parts of the chip

remain operational and the chip temperature is lowered

due to the decreased power dissipation in the transmitter

outputs. This protection is essential to protect against

bus line short-circuit induced damage. The activation of

the internal protection in one of the transceivers will not

affect the other one since these are fully independent.

1.5

Permanent Dominant Detection

The MCP25612FD device prevents two conditions:

• Permanent dominant condition on TXDX

• Permanent dominant condition on the bus

In Normal mode, if the MCP25612FD detects an

extended Low state on the TXDX input, it will disable the

CANHx and CANLx output drivers in order to prevent

the corruption of data on the CAN bus. The drivers will

remain disabled until TXDX goes to the High state.

In Standby mode, if the MCP25612FD detects an

extended Dominant condition on the bus, it will set the

RXDX pin to the Recessive state. This allows the

attached controller to go to Low-Power mode until the

dominant issue is corrected. RXDX is latched high until

a Recessive state is detected on the bus and the

wake-up function is enabled again.

Both conditions have a time-out of 1.25 ms (typical).

This implies a maximum bit time of 69.44 µs (14.4 kHz),

allowing up to 18 consecutive dominant bits on the bus.

The permanent dominant detection in one of the

transceivers will not affect the other one since these

are fully independent.

1.6

Power-on Reset (POR) and

Undervoltage Detection

The MCP25612FD has undervoltage detection on

the VDDX supply pin. The typical undervoltage

threshold is 4V.

When the device is powered on, CANHx and CANLx

remain in a High-Impedance state until VDDX exceeds

its undervoltage level. Once powered on, CANHx and

CANLx will enter a High-Impedance state if the voltage

level at VDDX drops below the undervoltage level,

providing voltage brown-out protection during normal

operation.

In Normal mode, the receiver output is forced to the

Recessive state during an undervoltage condition on

VDDX. In Standby mode, the low-power receiver is only

enabled when the VDDX supply voltage rises above its

undervoltage threshold. Once the threshold voltage is

reached, the low-power receiver is no longer controlled

by the POR comparator and remains operational down

to about 2.5V on the VDDX supply.

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