HWD487 データシートの表示（PDF） - Unspecified

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HWD487

Low-Power, Slew-Rate-Limited RS-485/RS-422 Transceivers

Unspecified 

Low-Power, Slew-Rate-Limited

RS-485/RS-422 Transceivers

10dB/div

10dB/div

0Hz

5MHz

500kHz/div

Figure 12. Driver Output Waveform and FFT Plot of HWD481/

HWD485/HWD490/HWD491/HWD1487 Transmitting a 150kHz

Signal

0Hz

5MHz

500kHz/div

Figure 13. Driver Output Waveform and FFT Plot of HWD483/

HWD487–HWD489 Transmitting a 150kHz Signal

Low-Power Shutdown Mode

(HWD481/HWD483/HWD487)

A low-power shutdown mode is initiated by bringing

both RE high and DE low. The devices will not shut

down unless both the driver and receiver are disabled.

In shutdown, the devices typically draw only 0.1µA of

supply current.

RE and DE may be driven simultaneously; the parts are

guaranteed not to enter shutdown if RE is high and DE

is low for less than 50ns. If the inputs are in this state

for at least 600ns, the parts are guaranteed to enter

shutdown.

For the HWD481, HWD483, and HWD487, the tZH and

tZL enable times assume the part was not in the low-

power shutdown state (the HWD485/HWD488–HWD491

and HWD1487 can not be shut down). The tZH(SHDN)

and tZL(SHDN) enable times assume the parts were shut

down (see Electrical Characteristics).

It takes the drivers and receivers longer to become

enabled from the low-power shutdown state

(tZH(SHDN), tZL(SHDN)) than from the

(tZH, tZL). (The parts are in operating

ompoedreatiinf gthemoR–—dE–e,

DE inputs equal a logical 0,1 or 1,1 or 0, 0.)

Driver Output Protection

Excessive output current and power dissipation caused

by faults or by bus contention are prevented by two

mechanisms. A foldback current limit on the output

stage provides immediate protection against short cir-

cuits over the whole common-mode voltage range (see

Typical Operating Characteristics). In addition, a ther-

mal shutdown circuit forces the driver outputs into a

high-impedance state if the die temperature rises

excessively.

Propagation Delay

Many digital encoding schemes depend on the differ-

ence between the driver and receiver propagation

delay times. Typical propagation delays are shown in

Figures 15–18 using Figure 14’s test circuit.

The difference in receiver delay times, | tPLH - tPHL |, is

typically under 13ns for the HWD481, HWD485,

HWD490, HWD491, and HWD1487 and is typically less

than 100ns for the HWD483 and HWD487–HWD489.

The driver skew times are typically 5ns (10ns max) for

the HWD481, HWD485, HWD490, HWD491, and

HWD1487, and are typically 100ns (800ns max) for the

HWD483 and HWD487–HWD489.

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