MAX4620/MAX4630/MAX4640
±15kV ESD-Protected, Low-Voltage, Quad,
SPST, CMOS Analog Switches
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±15kV ESD Protection
The MAX4620/MAX4630/MAX4640 are ±15kV ESD-pro-
tected at the NC/NO terminals. To accomplish this,
bidirectional SCRs are included on-chip between these
terminals. When the voltages at these terminals go
Beyond-the-Rails
TM
, the corresponding SCR turns on in
a few nanoseconds and bypasses the surge safely to
ground. This method is superior to using diode clamps
to the supplies because unless the supplies are very
carefully decoupled through low ESR capacitors, the
ESD current through the diode clamp could cause a
significant spike in the supplies. This may damage or
compromise the reliability of any other chip powered by
those same supplies.
There are diodes from NC/NO to the supplies in addi-
tion to the SCRs. There is a resistance in series with
each of these diodes to limit the current into the sup-
plies during an ESD strike. The diodes protect these
terminals from overvoltages that are not a result of ESD
strikes. These diodes also protect the device from
improper power-supply sequencing.
Once the SCR turns on because of an ESD strike, it
continues to be on until the current through it falls
below its “holding current.” The holding current is typi-
cally 110mA in the positive direction (current flowing
into the NC/NO terminal) at room temperature (see
Supply Current vs. Temperature in the Typical
Operating Characteristics). Design the system so that
any sources connected to NC/NO are current limited to
a value below the holding current to ensure the SCR
turns off when the ESD event is finished and normal
operation is resumed. Also, keep in mind that the hold-
ing current varies significantly with temperature. The
worst case is at +85°C when the holding currents drop
to 70mA. Since this is a typical number to guarantee
turn-off of the SCRs under all conditions, the sources
connected to these terminals should be current limited
to not more than half this value. When the SCR is
latched, the voltage across it is approximately 3V,
depending on the polarity of the pin current. The supply
voltages do not appreciably affect the holding current.
The sources connected to the COM side of the switch-
es do not need to be current limited since the switches
turn off internally when the corresponding SCR(s) latch-
es.
Even though most of the ESD current flows to GND
through the SCRs, a small portion of it goes into V+.
Therefore, it is a good idea to bypass the V+ with 0.1µF
capacitors directly to the ground plane.
ESD protection can be tested in various ways. Trans-
mitter outputs and receiver inputs are characterized for
protection to the following:
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method speci-
fied in IEC 1000-4-2 (formerly IEC 801-2)
• ±15kV using the Air-Gap Discharge method speci-
fied in IEC 1000-4-2 (formerly IEC 801-2)
ESD Test Conditions
Contact Maxim Integrated Products for a reliability
report that documents test setup, methodology, and
results.
Human Body Model
Figure 6 shows the Human Body Model, and Figure 7
shows the waveform it generates when discharged into
a low impedance. This model consists of a 100pF
capacitor charged to the ESD voltage of interest, which
can be discharged into the test device through a 1.5kΩ
resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and
performance of finished equipment; it does not specifi-
cally refer to ICs. The MAX4620/MAX4630/MAX4640
enable the design of equipment that meets Level 4 (the
highest level) of IEC 1000-4-2, without additional ESD
protection components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2. Because series resistance is
lower in the IEC 1000-4-2 ESD test model (Figure 8),
the ESD withstand voltage measured to this standard is
generally lower than that measured using the Human
Body Model. Figure 9 shows the current waveform for
the ±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge
test.
The Air-Gap test involves approaching the device with
a charged probe. The Contact Discharge method con-
nects the probe to the device before the probe is ener-
gized.
Chip Information
TRANSISTOR COUNT: 156
PROCESS: CMOS
Beyond-the-Rails is a trademark of Maxim Integrated Products.
