
ADG3123
Data Sheet
Rev. B | Page 10 of 12
THEORY OF OPERATION
voltage level translator. Fabricated on an enhanced LC2MOS
process, the device is capable of operating at high supply
voltages while maintaining ultralow power consumption.
The device requires a dual-supply voltage, VDDB and VSS, which
sets the low logic levels for all outputs and the high logic levels
for the Y7 and Y8 outputs. The VDDA pin acts as an analog input.
The voltage applied to the VDDA pin sets the output high logic
level for the Y1 to Y6 outputs.
The device translates the CMOS logic levels applied to the A1 to
A8 inputs into high voltage bipolar levels available on the Y side
of the device at Pin Y1 to Pin Y8.
To ensure proper operation, VDDB must always be greater than
or equal to VDDA and the voltage between the Pin VDDB and
Pin VSS should not exceed 35 V.
INPUT DRIVING REQUIREMENTS
T
he ADG3123 design ensures low input capacitance and leakage
current thereby reducing the loading of the circuit that drives the
input pins (Pin A1 to Pin A8) to a minimum. Its input threshold
levels are compliant with JEDEC standards for drivers operated
from supply voltages between 2.3 V and 5.5 V. It is recommended
that the inputs of any unused channel be tied to a stable logic
level (low or high).
OUTPUT LOAD REQUIREMENTS
The low output impedance of th
e ADG3123 allows each channel
to drive both resistive and capacitive loads. The maximum load
current is limited by the current carrying capability of any given
channel. If more channels are used, the maximum load current
per channel is reduced accordingly. Note that the sum of the
load currents on all channels should never exceed the absolute
maximum ratings specifications.
The average load current on each channel, ICHANNEL, can be
Capacitive Loads
ICHANNEL (A) = FO × CL × (VDDX + |VSS|)
where:
FO is the frequency of the signal applied to the channel in Hz.
CL is the load capacitance in farads.
VSS is the voltage applied to the VSS pin.
VDDX is VDDA for Y1 to Y6 outputs, and VDDB for Y7 to Y8 outputs.
Resistive Loads
L
SS
DDX
CHANNEL
R
V
D
V
D
A
I
×
+
×
=
)
1
(
)
(
where:
D is the duty cycle of the input signal. D is defined as the ratio
between the high state duration of the signal and its period.
RL is the load resistor in Ω.
VSS is the voltage applied to the VSS pin.
VDDX is VDDA for Y1 to Y6 outputs, and VDDB for Y7 to Y8 outputs.
POWER SUPPLIES
The
ADG3123 operates from a dual-supply voltage. As good
design practice for all CMOS devices dictates, power up the
ADG3123 first (VDDB and VSS) before applying the signals to its inputs (A1 to A8 and VDDA). To ensure correct operation of the
ADG3123, the voltage applied to the VDDB pin must always be greater than or equal to VDDA and the voltage between the
Pin VDDB and Pin VSS should not exceed 35 V.
To ensure optimum performance, use decoupling capacitors on
all power supply pins. Furthermore, good engineering and layout
practice suggests placing these capacitors as close as possible to
the package supply pins.