MAX4551/MAX4552/MAX4553
±15kV ESD-Protected, Quad,
Low-Voltage, SPST Analog Switches
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Applications Information
MAX4551/MAX4552/MAX4553
±15kV ESD Protection
The MAX4551/MAX4552/MAX4553 are ±15kV ESD-pro-
tected according to IEC 1000-4-2 at their NC/NO pins.
To accomplish this, bidirectional SCRs are included on-
chip between these pins and the GND pin. In normal
operation, these SCRs are off and have negligible
effect on the performance of the switches. When there
is an ESD strike at these pins, however, the voltages at
these pins go Beyond-the-Rails™ and cause the corre-
sponding SCR(s) to turn on in a few nanoseconds and
bypass 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 reliabili-
ty of any other chip powered by those same supplies.
In the MAX4551/MAX4552/MAX4553, there are diodes
to the supplies in addition to the SCRs at the NC/NO
pins, but there is a resistance in series with these
diodes to limit the current into the supplies during an
ESD strike. The diodes are present to protect these
pins from overvoltages that are not as a result of ESD
strikes like those that may occur due to 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 pin) and 95mA in the negative direction
at room temperature (see SCR Holding Current vs.
Temperature in the
Typical Operating Characteristics
).
The system should be designed such that any sources
connected to these pins are current limited to a value
below these to make sure the SCR turns off when the
ESD event gets over to resume normal operation. Also,
keep in mind that the holding current varies significant-
ly with temperature. At +85°C, which represents the
worst case, the holding currents drop to 70mA and
65mA in the positive and negative directions respec-
tively. Since these are typical numbers, to get guaran-
teed turn-off of the SCRs under all conditions, the
sources connected to these pins should be current lim-
ited to not more than half these values. When the SCR
is latched, the voltage across it is about ±3V, depend-
ing on the polarity of the pin current. The supply volt-
ages do not affect the holding currents appreciably.
The sources connected to the COM side of the switches
do not need to be current limited since the switches are
made to turn off internally when the corresponding
SCR(s) get latched.
Even though most of the ESD current flows to GND
through the SCRs, a small portion of it goes into the
supplies. Therefore, it is a good idea to bypass the
supply pins with 100nF 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 for a reliability report that documents
test setup, methodology, and results.
Human Body Model
Figure 8 shows the Human Body Model, and Figure 9
shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
est, which is then 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 integrated circuits. The MAX4551/MAX4552/
MAX4553 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 10),
the ESD withstand voltage measured to this standard
is generally lower than that measured using the
Human Body Model. Figure 11 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
connects the probe to the device before the probe is
energized.
Beyond-the-Rails is a trademark of Maxim Integrated Products.
