MAX3070E 查看數據表（PDF） - Maxim Integrated

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MAX3070E

+3.3V / 15kV ESD-Protected / Fail-Safe / Hot-Swap / RS-485/RS-422 Transceivers

Maxim Integrated 

+3.3V, ±15kV ESD-Protected, Fail-Safe,

Hot-Swap, RS-485/RS-422 Transceivers

RC

RD

1MΩ

1500Ω

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

HIGH-

VOLTAGE

DC

SOURCE

Cs

100pF

STORAGE

CAPACITOR

DEVICE

UNDER

TEST

Figure 10a. Human Body ESD Test Model

RC

50MΩ TO 100MΩ

RD

330Ω

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

HIGH-

VOLTAGE

DC

SOURCE

Cs

150pF

STORAGE

CAPACITOR

DEVICE

UNDER

TEST

Figure 10c. IEC 1000-4-2 ESD Test Model

current in IEC 1000-4-2, because series resistance is

lower in the IEC 1000-4-2 model. Hence, the ESD with-

stand voltage measured to IEC 1000-4-2 is generally

lower than that measured using the Human Body Model.

Figure 10c shows the IEC 1000-4-2 model, and Figure

10d shows the current waveform for IEC 1000-4-2 ESD

Contact Discharge test.

The air-gap test involves approaching the device with a

charged probe. The contact-discharge method connects

the probe to the device before the probe is energized.

Machine Model

The machine model for ESD tests all pins using a

200pF storage capacitor and zero discharge resis-

tance. The objective is to emulate the stress caused

when I/O pins are contacted by handling equipment

during test and assembly. Of course, all pins require

this protection, not just RS-485 inputs and outputs.

IP 100%

90%

Ir

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

AMPS

36.8%

10%

0

0 tRL

TIME

tDL

CURRENT WAVEFORM

Figure 10b. Human Body Current Waveform

I

100%

90%

10%

tr = 0.7ns TO 1ns

30ns

t

60ns

Figure 10d. IEC 1000-4-2 ESD Generator Current Waveform

Applications Information

256 Transceivers on the Bus

The standard RS-485 receiver input impedance is 12kΩ

(1-unit load), and the standard driver can drive up to 32-

unit loads. The MAX3070E family of transceivers has a

1/8-unit load receiver input impedance (96kΩ), allowing

up to 256 transceivers to be connected in parallel on one

communication line. Any combination of these devices

as well as other RS-485 transceivers with a total of 32-

unit loads or fewer can be connected to the line.

Reduced EMI and Reflections

The MAX3070E/MAX3071E/MAX3072E feature reduced

slew-rate drivers that minimize EMI and reduce reflec-

tions caused by improperly terminated cables, allowing

error-free data transmission up to 250kbps. The

MAX3073E/MAX3074E/MAX3075E offer higher driver

output slew-rate limits, allowing transmit speeds up to

500kbps. The MAX3079E with SRL = VCC or uncon-

nected, are slew-rate limited. With SRL unconnected,

the MAX3079E error-free data transmission is up to

250kbps; with SRL connected to VCC the data transmit

speeds up to 500kbps.

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