_______________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).

±15kV ESD-Protected, Low-Voltage, CMOS

Analog Multiplexers/Switches

_______________________________________________________________________________________

9

Table 1. Truth Table/Switch Programming

ENABLE

INPUT

C*

B

A

SELECT INPUTS

X

X

L

L

L

L

X

H

H

L

L

H

L

L

H

H

L

L

H

L

L

L

L

L

H

L

H

L

L

H

H

L

H

H

H

L

X-X0, Y-Y1, Z-Z1

MAX4558

MAX4559

MAX4560

X-X2, Y-Y2

X-X6

ON SWITCHES

X-X1, Y-Y1, Z-Z1

X-X3, Y-Y3

X-X7

All switches open

All switches open

X-X0, Y-Y0, Z-Z0

X-X0, Y-Y0

X-X0

All switches open

X-X1, Y-Y0, Z-Z0

X-X1, Y-Y1

X-X0, Y-Y1, Z-Z0

X-X2, Y-Y2

X-X2

X-X1, Y-Y1, Z-Z0

X-X3, Y-Y3

X-X0, Y-Y0, Z-Z1

X-X0, Y-Y0

X-X4

X-X3

X-X1

X-X1, Y-Y0, Z-Z1

X-X1, Y-Y1

X-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.