_______________Detailed Description
The MAX4558/MAX4559/MAX4560 are ESD protected
(per IEC 1000-4-2) at their X, Y, Z output pins and X_,
Y_, Z_ input pins. These ICs feature on-chip bidirection-
al silicon-controlled rectifiers (SCRs) between the pro-
tected pins and GND. The SCRs are normally off and
have a negligible effect on the switches’ performance.
During an ESD strike, the voltages at the protected pins
go Beyond-the-Rails™, causing the corresponding
SCR(s) to turn on in a few nanoseconds. This bypasses
the surge current safely to ground. This protection
method is superior to using diode clamps to the sup-
plies. Unless the supplies are very carefully decoupled
through low-ESR capacitors, the ESD current through a
diode clamp could cause a significant spike in the sup-
plies, which might damage or compromise the reliabili-
ty of any other chip powered by those same supplies.
In addition to the SCRs at the ESD-protected pins,
these devices provide internal diodes connected to the
supplies. Resistors placed in series with these diodes
limit the current flowing into the supplies during an ESD
strike. The diodes protect the X, Y, Z and X_, Y_, Z_
pins from overvoltages due to improper power-supply
sequencing.
Once the SCR turns on because of an ESD strike, it
remains on until the current through it falls below its
“holding current.” The holding current is typically
110mA in the positive direction (current flowing into the
pin) and 95mA in the negative direction at room tem-
perature (see SCR Holding Current vs. Temperature in
the
Typical Operating Characteristics
). The system
should be designed so that any sources connected to
the X, Y, Z or X_, Y_, Z_ pins are current limited to a
value below the holding current. This ensures that the
SCR turns off and normal operation resumes after an
ESD event.
Keep in mind that the holding currents vary significantly
with temperature; they drop to 70mA (typ) in the posi-
tive direction and 65mA (typ) in the negative direction,
at +85°C worst case. To guarantee turn-off of the SCRs
under all conditions, current limit the sources connect-
ed to these pins to not more than half of these typical
values. When the SCR is latched, the voltage across it
is about ±3V, depending on the polarity of the pin cur-
rent. The supply voltages do not affect the holding cur-
rents appreciably. When one or more SCRs turn on
because of an ESD event, all switches in the part turn
off to prevent current through the switch(es) from sus-
taining latchup.
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 to the ground plane.
__________Applications Information
ESD Protection
The MAX4558/MAX4559/MAX4560 are characterized
for protection to the following:
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method specified
in IEC 1000-4-2 (formerly IEC 801-2)
• ±12kV using the Air-Gap Discharge method speci-
fied in IEC 1000-4-2 (formerly IEC 801-2).
MAX4558/MAX4559/MAX4560
±15kV ESD-Protected, Low-Voltage, CMOS
Analog Multiplexers/Switches
_______________________________________________________________________________________ 9
Table 1. Truth Table/Switch Programming
ENABLE
INPUT
C* B A
SELECT INPUTS
XX
LLLL
XH
HL
LHLL
HH
LLHL
LL
LL
HLHL
LHHL
HHHL
X-X0, Y-Y1, Z-Z1
MAX4558 MAX4559 MAX4560
X-X2, Y-Y2X-X6
ON SWITCHES
X-X1, Y-Y1, Z-Z1X-X3, Y-Y3X-X7
All switches openAll switches open
X-X0, Y-Y0, Z-Z0X-X0, Y-Y0X-X0
All switches open
X-X1, Y-Y0, Z-Z0X-X1, Y-Y1
X-X0, Y-Y1, Z-Z0X-X2, Y-Y2X-X2
X-X1, Y-Y1, Z-Z0X-X3, Y-Y3
X-X0, Y-Y0, Z-Z1X-X0, Y-Y0X-X4
X-X3
X-X1
X-X1, Y-Y0, Z-Z1X-X1, Y-Y1X-X5
X = Don’t care * C not present on MAX4559.
Note: Input and output pins are identical and interchangeable. Either may be considered an input or output; signals pass equally well in
either direction.
Beyond-the-Rails is a trademark of Maxim Integrated Products.
