MAX3057ASA データシートの表示（PDF） - Maxim Integrated

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MAX3057ASA

±80V Fault-Protected, 2Mbps, Low-Supply Current CAN Transceivers

Maxim Integrated 

MAX3050/MAX3057

±80V Fault-Protected, 2Mbps, Low-Supply

Current CAN Transceivers

AutoShutdown (MAX3050)

To manage power consumption, AutoShutdown puts the

device into shutdown mode after it has been inac-tive

for a period of time. The value of an external capacitor

(CSHDN) connected to SHDN determines the threshold

of inactivity time, after which the AutoShutdown triggers.

Floating SHDN allows the MAX3050 to automatically

change from active mode to shutdown.

Use a 100nF capacitor as CSHDN for a typical threshold

of 20ms. Change the capacitor value according to the

following equation to change the threshold time period.

( ) C

SHDN

(nF)

=

I

SHDN (mA )× time(µs)

VCC − VSHDN

Drive SHDN high to turn the MAX3050 on and disable

AutoShutdown.

When the MAX3050 is in shutdown mode, only the wake-

up comparator is active, and normal bus communication

is ignored. The remote master of the CAN system wakes

up the MAX3050 with a signal greater than 9V on CANH.

Internal circuitry in the MAX3050 puts the device in nor-

mal operation by driving SHDN high.

The MAX3057 does not have the AutoShutdown feature.

Driver Output Protection

The MAX3050 and MAX3057 have several features that

protect them from damage. Thermal shutdown switches

off the device and puts CANH and CANL into high

impedance if the junction temperature exceeds +160°C.

Thermal protection is needed particularly when a bus line

is short-circuited. The hysteresis for the thermal shutdown

is approximately 20°C.

Additionally, a current-limiting circuit protects the trans-

mitter output stage against short-circuit to positive and

negative battery voltage. Although the power dissipation

increases during this fault condition, this feature prevents

destruction of the transmitter output stage.

Applications Information

Reduced EMI and Reflections

In slope-control mode, the CANH and CANL outputs are

slew-rate limited, minimizing EMI and reducing reflections

caused by improperly terminated cables. In general, a

transmitter’s rise time relates directly to the length of an

unterminated stub, which can be driven with only minor

waveform reflections. The following equation expresses

this relationship conservatively:

Length = tRISE / (15ns/ft)

where tRISE is the transmitter’s rise time.

www.maximintegrated.com

CANH - CANL

1V/div

FFT

500mV/div

Figure 5. FFT Dominant Bus at 2Mbpslayout.

CANH - CANL

1V/div

FFT

200mV/div

Figure 6. FFT Recessive Bus at 2Mbps

CANH - CANL

1V/div

FFT

500mV/div

Figure 7. FFT Dominant Bus at 500kbps

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