MAX3070E Maxim, MAX3070E Datasheet - Page 17

• Manufacturer Part Number: MAX3070E
• Description: +3.3V / 15kV ESD-Protected / Fail-Safe / Hot-Swap / RS-485/RS-422 Transceivers
• Manufacturer: Maxim

Figure 10a. Human Body ESD Test Model
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.
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.
VOLTAGE
SOURCE
HIGH-
VOLTAGE
SOURCE
DC
HIGH-
DC
CHARGE-CURRENT-
CHARGE-CURRENT-
LIMIT RESISTOR
LIMIT RESISTOR
50MΩ TO 100MΩ
1MΩ
R
R
C
100pF
C
150pF
______________________________________________________________________________________
C s
C s
Hot-Swap, RS-485/RS-422 Transceivers
+3.3V, ±15kV ESD-Protected, Fail-Safe,
RESISTANCE
STORAGE
CAPACITOR
DISCHARGE
RESISTANCE
DISCHARGE
STORAGE
CAPACITOR
1500Ω
330Ω
R
R
D
D
Machine Model
DEVICE
UNDER
TEST
DEVICE
UNDER
TEST
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.
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 = V
nected, are slew-rate limited. With SRL unconnected,
the MAX3079E error-free data transmission is up to
250kbps; with SRL connected to V
speeds up to 500kbps.
Figure 10b. Human Body Current Waveform
Figure 10d. IEC 1000-4-2 ESD Generator Current Waveform
t
AMPS
r
= 0.7ns TO 1ns
I
P
36.8%
100%
90%
10%
100%
0
90%
10%
0
I
t
RL
Applications Information
Reduced EMI and Reflections
256 Transceivers on the Bus
30ns
CURRENT WAVEFORM
TIME
60ns
t
DL
I r
CC
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
the data transmit
CC
or uncon-
t
17