MAX14782E_14 Datasheet, PDF (14/17 Pages) Maxim Integrated Products – 500Kbps 3.3V to 5V RS-485/RS-422 Transceiver with ±35kV HBM ESD Protection

MAX14782E
500Kbps 3.3V to 5V RS-485/RS-422 Transceiver
with ±35kV HBM ESD Protection
on M1. Transistors M2 (a 500µA current sink) and M1 (a
100µA current sink) pull DE to GND through a 5kΩ (typ)
resistor. M2 is designed to pull DE to the disabled state
against an external parasitic capacitance up to 100pF that
can drive DE high. After 10µs, the timer deactivates M2
while M1 remains on, holding DE low against three-state
leakages that can drive DE high. M1 remains on until an
external source overcomes the required input current.
At this time, the SR latch resets and M1 turns off. When
M1 turns off, DE reverts to a standard, high-impedance
CMOS input. Whenever V_CC drops below 1V, the hot-
swap input is reset.
A complementary circuit employing two pMOS devices
pulls RE to V_CC.
±35kV ESD Protection
ESD protection structures are incorporated on all pins
to protect against electrostatic discharges encountered
during handling and assembly. The driver outputs and
receiver inputs of the MAX14782E have extra protection
against static electricity. The ESD structures withstand
high ESD in all states: normal operation, shutdown, and
powered down. After an ESD event, the MAX14782E
keeps working without latch-up or damage.
ESD protection can be tested in various ways. The trans-
mitter outputs and receiver inputs of the MAX14782E are
characterized for protection to the following limits:
● ±35kV HBM
● ±20kV using the Air-Gap Discharge method specified
in IEC 61000-4-2
● ±12kV using the Contact Discharge method specified
in IEC 61000-4-2
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents test
setup, test methodology, and test results.
Human Body Model (HBM)
Figure 10 shows the HBM, and Figure 11 shows the cur-
rent waveform it generates when discharged into a low-
impedance state. This model consists of a 100pF capaci-
tor charged to the ESD voltage of interest, which is then
discharged into the test device through a 1.5kΩ resistor.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD testing and per-
formance of finished equipment. However, it does not spe-
cifically refer to integrated circuits. The MAX14782E helps
in designing equipment to meet IEC 61000-4-2 without the
need for additional ESD protection components.
The major difference between tests done using the HBM
and IEC 61000-4-2 is higher peak current in IEC 61000-
4-2 because series resistance is lower in the IEC 61000-
4-2 model. Hence, the ESD withstand voltage measured
to IEC 61000-4-2 is generally lower than that measured
using the HBM.
RC
RD
1MΩ
1.5kΩ
CHARGE CURRENT-
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
SOURCE
CS
100pF
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 10. Human Body ESD Test Model
IP 100%
90%
AMPERES
36.8%
10%
0
0 _tRL
IR
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
TIME
t_DL
CURRENT WAVEFORM
Figure 11. Human Body Current Waveform
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