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ISL8499

Ultra Low ON-Resistance, +1.65V to +4.5V, Single Supply, Quad SPDT (Dual DPDT) Analog Switch

Renesas Electronics 

ISL8499

approach, but the switch signal range is reduced and the

resistance may increase, especially at low supply voltages.

OPTIONAL

PROTECTION

RESISTOR

INX

VNO or NC

OPTIONAL PROTECTION

DIODE

V+

VCOM

GND

OPTIONAL PROTECTION

DIODE

FIGURE 8. OVERVOLTAGE PROTECTION

Power-Supply Considerations

The ISL8499 construction is typical of most single supply

CMOS analog switches, in that they have two supply pins: V+

and GND. V+ and GND drive the internal CMOS switches and

set their analog voltage limits. Unlike switches with a 4V

maximum supply voltage, the ISL8499 4.7V maximum supply

voltage provides plenty of room for the 10% tolerance of 4.3V

supplies, as well as room for overshoot and noise spikes.

The minimum recommended supply voltage is 1.65V but will

operate with a supply voltage below 1.5V. It is important to note

that the input signal range, switching times, and on-resistance

degrade at lower supply voltages. Refer to the “Electrical

Specification” tables starting on page 3 and “Typical

Performance” curves starting on page 6 for details.

V+ and GND also power the internal logic and level shiftiers.

The level shiftiers convert the input logic levels to switched V+

and GND signals to drive the analog switch gate terminals.

This family of switches cannot be operated with bipolar

supplies, because the input switching point becomes negative

in this configuration.

Logic-Level Thresholds

This switch family is 1.8V CMOS compatible (0.5V and 1.4V)

over a supply range of 2.7V to 4.5V (see Figure 14). At 2.7V

the VIL level is about 0.52V. This is still above the 1.8V CMOS

guaranteed low output maximum level of 0.5V, but noise

margin is reduced.

The digital input stages draw supply current whenever the

digital input voltage is not at one of the supply rails. Driving the

digital input signals from GND to V+ with a fast transition time

minimizes power dissipation. The ISL8499 has been designed

to minimize the supply current whenever the digital input

voltage is not driven to the supply rails (0V to V+). For example

driving the device with 2.85V logic (0V to 2.85V) while

operating with a 4.2V supply the device draws only 6A of

current (see Figure 21 for VIN = 2.85V).

High-Frequency Performance

In 50 systems, the signal response is reasonably flat even

past 30MHz with a -3dB bandwidth of 104MHz (see Figure 17).

The frequency response is very consistent over a wide V+

range, and for varying analog signal levels.

An OFF switch acts like a capacitor and passes higher

frequencies with less attenuation, resulting in signal

feedthrough from a switch’s input to its output. Off Isolation is

the resistance to this feedthrough, while Crosstalk indicates the

amount of feedthrough from one switch to another. Figure 18

details the high Off Isolation and Crosstalk rejection provided

by this part. At 100kHz, Off Isolation is about 68dB in 50

systems, decreasing approximately 20dB per decade as

frequency increases. Higher load impedances decrease Off

Isolation and Crosstalk rejection due to the voltage divider

action of the switch OFF impedance and the load impedance.

Leakage Considerations

Reverse ESD protection diodes are internally connected between

each analog-signal pin and both V+ and GND. One of these

diodes conducts if any analog signal exceeds V+ or GND.

Virtually all the analog leakage current comes from the ESD

diodes to V+ or GND. Although the ESD diodes on a given

signal pin are identical and therefore fairly well balanced, they

are reverse biased differently. Each is biased by either V+ or

GND and the analog signal. This means their leakages will

vary as the signal varies. The difference in the two diode

leakages to the V+ and GND pins constitutes the analog-

signal-path leakage current. All analog leakage current flows

between each pin and one of the supply terminals, not to the

other switch terminal. This is why both sides of a given switch

can show leakage currents of the same or opposite polarity.

There is no connection between the analog signal paths and

V+ or GND.

FN6111 Rev 3.00

February 5, 2008

Page 8 of 14

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