±15kV ESD-Protected, Low-Voltage,

SPDT/SPST, CMOS Analog Switches

7

±15kV ESD Protection

The MAX4561/MAX4568/MAX4569 are ±15kV ESD-pro-

tected at the NC/NO terminals in accordance with

IEC1000-4-2. To accomplish this, bidirectional SCRs

are included on-chip between these terminals. When

the voltages at these terminals go Beyond-the-Rails™,

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 decou-

pled 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. A resistance in series with each of

these diodes limits the current into the supplies 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

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 NC/NO terminal) at room temperature (see

SCR Holding 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 resumes. Also, remember that the holding

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 con-

nected to these terminals should be current-limited to

no more than half this value. When the SCR is latched,

the voltage across it is approximately 3V. The supply

voltages do not affect the holding current appreciably.

The sources connected to the COM side of the switches

need not be current limited since the switches turn off

internally when the corresponding SCR(s) latch.

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. 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 dis-

charged into the test device through a 1.5k

Ω 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 MAX4561 enables

the design of equipment that meets Level 4 (the highest

level) of IEC 1000-4-2, without additional ESD protec-

tion components.

The major difference between tests done using the

Human Body Model and IEC 1000-4-2 is higher peak cur-

rent 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 connects

the probe to the device before the probe is energized.

Chip Information

PROCESS: CMOS

Beyond-the-Rails is a trademark of Maxim Integrated Products.