ISL43112 Datasheet, PDF (6/11 Pages) Intersil Corporation – Low-Voltage, Dual Supply, SPST, High Performance Analog Switches

ISL43112, ISL43113
Test Circuits and Waveforms (Continued)
V+
IMPEDANCE
ANALYZER
NO or NC
COM
IN ^{V- or V+}
V-
FIGURE 5. CAPACITANCE TEST CIRCUIT
Detailed Description
The ISL43112 and ISL43113 analog switches offer precise
switching capability from ±1.5V to ±6V supplies with low on-
resistance (15Ω) and high speed operation (t_ON = 40ns,
t_OFF = 25ns). The devices are especially well suited to
portable battery powered equipment thanks to the low
operating supply voltage (±1.5V), low power consumption
(250µW), low leakage currents (2nA max), and the tiny
SOT-23 packaging. High frequency applications also benefit
from the wide bandwidth, and the very high off isolation.
Supply Sequencing And Overvoltage Protection
As 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 6). 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 1kΩ
resistor in series with the input (see Figure 6).
OPTIONAL
PROTECTION
RESISTOR _IN
V_{NO or NC}
OPTIONAL PROTECTION
DIODE
V+
V_COM
V-
OPTIONAL PROTECTION
DIODE
FIGURE 6. OVERVOLTAGE PROTECTION
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.
Adding a series resistor to the switch input defeats the
purpose of using a low R_ON switch, so two small signal
diodes can be added in series with the supply pins to provide
overvoltage protection for all pins (see Figure 6). 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 ISL4311X construction is typical of most CMOS analog
switches, except that there are only two supply pins: V+ and
V-. The power supplies need not be symmetrical for useful
operation. As long as the total supply voltage (V+ to V-,
including supply tolerances, overshoot, and noise spikes) is
less than the 15V maximum supply rating, and the digital
input switching point remains reasonable (see “Logic-Level
Thresholds” section), the ISL43112/13 function well. The
15V maximum supply rating provides the designer of 12V
systems much greater flexibility than switches with a 13V
maximum supply voltage.
The minimum recommended supply voltage is ±1.5V. It is
important to note that the input signal range, switching times,
and on-resistance degrade at lower supply voltages, and the
digital input V_IL becomes negative at V_S ≤ ±2V. Refer to the
“Typical Performance” curves for details.
V+ and V- power the internal CMOS switches and set their
analog voltage limits. These supplies also power the internal
logic and level shifters. The level shifters convert the input
logic levels to switched V+ and V- signals to drive the analog
switch gate terminals.
This family of switches is not recommended for single supply
applications. For single supply, similar performance, pin
6