ADG46+1/ADG46+3
THEORY OF OPERATION
V
DD by a threshold voltage, VT, the switch turns off and is in
The ADG4612/ADG4613 contain four independent single-
pole/single-throw (SPST) switches. Each switch is rail-to-rail
and conducts equally well in both directions when on.
isolation mode.
If the analog input signal exceeds the negative supply, VSS, when
the switch is off, the switch blocks a signal up to −5.5 V. If the
switch is on, the switch remains on, and this signal is passed to
the output. See the Negative Fault Condition; Negative Signal
Handling section for more details.
The ADG4612/ADG4613 has two modes of operation: normal
mode and isolation mode.
The operation modes are made possible by a special detection
circuitry that monitors the voltage levels at the source or drain
terminals and VDD relative to ground. Depending on these
voltage levels, the device operates in normal mode or isolation
mode accordingly.
Isolation Mode
In isolation mode, all switches are in the off condition. The
switch inputs are isolated from the switch outputs. The switch
inputs are high impedance inputs with greater than 475 kΩ
impedance to VDD ground and across the switch. This prevents
any current from flowing that can damage the switch. This is
very useful in applications where analog signals may be present
at the switch inputs before power is present or where the user
has no control over the power supply sequence.
Isolation mode is a useful feature that isolates the inputs from
the outputs where input signals may be present before supplies
or during positive fault conditions that can occur in applications.
Normal Mode
In normal mode, the switch functions as a normal 4 × SPST
switch, whereby the switch is controlled by the logic input pins,
IN1 to IN4.
The switch is in isolation mode when
•
No power supplies are present, that is, when VDD is floating
or VDD ≤ 1 V; or
The following three conditions need to be satisfied for the
switch to be in the on condition;
•
Input signal, VS, VD > VDD + VT
•
•
•
VDD ≥ 2.7 V; and
Input signal, VS, VD < VDD + VT ; and
Logic input, INx set to on level
The negative supply rail, VSS, can be floating or 0 V to −5.5 V.
The ground pin must be connected to the ground potential.
When the switch is in the on condition, if the signal range is
from VDD to −5.5 V, the signals present on the switch inputs are
passed through to the switch output. If the analog input exceeds
Table 11. Switch Operation Mode
VS, VD
Switch
Mode
1
VDD
VSS
GND
(Input Voltage, Sx or Dx)
−5.5 V to +10.5 V
0 V to 16 V
−5.5 V to +10.5 V
0 V to 16 V
Switch Condition
Floating
X
0 V
All switches off
Inputs isolated from outputs
All switches off
Inputs isolated from outputs
All switches off
Inputs isolated from outputs
Isolation
0 V to 0.8 V
X
0 V
0 V
0 V
Isolation
Isolation
Normal
VDD ≥ 2.± V
X
VS, VD > VDD + VT
VDD ≥ 2.± V to 16 V
0 V to −5.5 V
VDD to VDD – 16 V
Switch state is determined by logic
levels, INx
1 X = don’t care; for example, floating, 0 V to −5.5 V.
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