adg3308 Analog Devices, Inc., adg3308 Datasheet - Page 16

• Manufacturer Part Number: adg3308
• Description: Low Voltage 1.15 V To 5.5 V, Bidirectional, Logic Level Translators
• Manufacturer: Analog Devices, Inc.

ADG3308/ADG3308-1
THEORY OF OPERATION
The ADG3308/ADG3308-1 level translators allow the level
shifting necessary for data transfer in a system where multiple
supply voltages are used. The device requires two supplies, V
and V
each side of the device. When driving the A pins, the device
translates the V
logic levels available at the Y pins. Similarly, because the device
is capable of bidirectional translation, when driving the Y pins
the V
compatible logic levels available at the A pins. When EN = 0,
the A1 pin to the A8 and the Y1 pin to the Y8 pin are three-
stated. When EN is driven high, the ADG3308/ADG3308-1 go
into normal operation mode and perform level translation.
LEVEL TRANSLATOR ARCHITECTURE
The ADG3308/ADG3308-1 consist of eight bidirectional
channels. Each channel can translate logic levels in either the
A→Y or the Y→A direction. It uses a one-shot accelerator archi-
tecture, ensuring excellent switching characteristics.
shows a simplified block diagram of a bidirectional channel.
The logic level translation in the A
using a level translator (U1) and an inverter (U2), whereas the
translation in the Y
inverter and U4 inverter. The one-shot generator detects a rising
or falling edge present on either the A side or the Y side of the
channel. It sends a short pulse that turns on the PMOS transis-
tors (T1 and T2) for a rising edge, or the NMOS transistors (T3
and T4) for a falling edge. This charges/discharges the capacitive
load faster, resulting in fast rise and fall times.
The inputs of the unused channels (A or Y) should be tied to
their corresponding V
Figure 39. Simplified Block Diagram of an ADG3308/ADG3308-1 Channel
CCY
CCY
A
-compatible logic levels are translated to the V
(V
T1
T4
V
CCA
CCA
CCA
≤ V
6kΩ
-compatible logic levels to V
→
P
CCY
A direction is performed using the U3
ONE-SHOT GENERATOR
CC
). These supplies set the logic levels on
U1
U4
rail (V
U2
U3
CCA
→
or V
Y direction is performed
6kΩ
CCY
N
) or to GND.
V
CCY
CCY
T3
T2
-compatible
Y
Figure 39
CCA
-
Rev. A | Page 16 of 20
CCA
INPUT DRIVING REQUIREMENTS
To ensure correct operation of the ADG3308/ADG3308-1, the
circuit that drives the input of the ADG3308/ADG3308-1 chan-
nels should have an output impedance of less than or equal to
150 Ω and a minimum current driving capability of 36 mA.
OUTPUT LOAD REQUIREMENTS
The ADG3308/ADG3308-1 level translators are designed to
drive CMOS-compatible loads. If current-driving capability is
required, it is recommended to use buffers between the
ADG3308/ADG3308-1 outputs and the load.
ENABLE OPERATION
The ADG3308/ADG3308-1 provide three-state operation at the
A I/O pin and the Y I/O pin by using the enable (EN) pin, as
shown in
Table 4. Truth Table
EN
0
1
1
2
When EN = 0, the ADG3308/ADG3308-1 enter into three-state
mode. In this mode, the current consumption from both the
V
power, which is critical, especially on battery-operated systems.
The EN input pin can only be driven with V
logic levels for the ADG3308, whereas the ADG3308-1 can be
driven with either V
POWER SUPPLIES
For proper operation of the ADG3308/ADG3308-1, the voltage
applied to the V
age applied to V
power-up sequence is V
ADG3308-1 operate properly only after both supply voltages
reach their nominal values. It is not recommended to use the part
in a system where, during power-up, V
V
V
should be decoupled to GND as close as possible to the device.
High impedance state.
In normal operation, the ADG3308/ADG3308-1 perform level translation.
CCA
CCY
CCA
due to a significant increase in the current taken from the
and V
supply. For optimum performance, the V
Table 4.
CCY
supplies is reduced, allowing the user to save
Y I/O Pins
High-Z
Normal operation
CCY
CCA
. To meet this condition, the recommended
must always be less than or equal to the volt-
CCA
1
- or V
CCY
first and then V
CCY
-compatible logic levels.
2
A I/O Pins
High-Z
Normal operation
CCA
might be greater than
CCA
CCY
1
. The ADG3308/
CCA
-compatible
and V
2
CCY
pins