ISL43681IRZ datasheet(13/18 Pages) RENESAS

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ISL43681, ISL43741

FN6053 Rev 3.00

Page 13 of 18

Mar 13, 2006

Detailed Description

The ISL43681 and ISL43741 multiplexers offer precise

switching capability from a bipolar 2V to 6V or a single 2V

to 12V supply with low on-resistance (39

) and high speed

operation (tON = 38ns, tOFF = 19ns) with dual 5V supplies.

They have an inhibit and inhibit bar pin to simultaneously

open all signal paths. They also have a latch bar pin to lock

in the last switch address.

The devices are especially well suited for applications using

±5V supplies. With ±5V supplies the performance (RON,

Leakage, Charge Injection, etc.) is best in class.

High frequency applications also benefit from the wide

bandwidth, and the very high off isolation and crosstalk

rejection.

Supply Sequencing And Overvoltage Protection

With any CMOS device, proper power supply sequencing is

required to protect the device from excessive input currents

which might permanently damage the IC. All I/O pins contain

ESD protection diodes from the pin to V+ and to V- (see

Figure 9). To prevent forward biasing these diodes, V+ and

V- must be applied before any input signals, and input signal

voltages must remain between V+ and V-. If these conditions

cannot be guaranteed, then one of the following two

protection methods should be employed.

Logic inputs can easily be protected by adding a 1k



resistor in series with the input (see Figure 9). The resistor

limits the input current below the threshold that produces

permanent damage, and the sub-microamp input current

produces an insignificant voltage drop during normal

operation.

This method is not applicable for the signal path inputs.

Adding a series resistor to the switch input defeats the

purpose of using a low RON switch, so two small signal

diodes can be added in series with the supply pins to provide

overvoltage protection for all pins (see Figure 9). These

additional diodes limit the analog signal from 1V below V+ to

1V above V-. The low leakage current performance is

unaffected by this approach, but the switch resistance may

increase, especially at low supply voltages.

Power-Supply Considerations

The ISL43681 and ISL43741 construction is typical of most

CMOS analog switches, in that they have three supply pins:

V+, V-, and GND. V+ and V- drive the internal CMOS

switches and set their analog voltage limits, so there are no

connections between the analog signal path and GND.

Unlike switches with a 13V maximum supply voltage, the

ISL43681 and ISL43741 15V maximum supply voltage

provides plenty of room for the 10% tolerance of 12V

supplies (6V or 12V single supply), as well as room for

overshoot and noise spikes.

This family of switches performs equally well when operated

with bipolar or single voltage supplies.The minimum

FIGURE 7. CROSSTALK TEST CIRCUIT

FIGURE 8. CAPACITANCE TEST CIRCUIT

Test Circuits and Waveforms (Continued)

0V or V+

ANALYZER

NOA or NCA

SIGNAL

GENERATOR

GND

ADDX



N.C.

COMB

NOB or NCB

V-

V+

COMA

EN, LE

ISL43741

GND

NO or NC

COM

ADDX

IMPEDANCE

ANALYZER

0V or V+

V-

V+

EN, LE

FIGURE 9. INPUT OVERVOLTAGE PROTECTION

VCOM

VNO or NC

OPTIONAL PROTECTION

V+

LOGIC

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

FOR LOGIC

INPUTS



V-

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