Datasheet

Data Sheet AD5263
Rev. F | Page 21 of 28
MULTIPLE DEVICES ON ONE BUS
Figure 49 shows four AD5263 devices on the same serial bus. Each
has a different slave address because the states of their AD0 and
AD1 pins are different. This allows each RDAC within each device
to be written to or read from independently. The master device
output bus line drivers are open-drain, pull-downs in a fully
I
2
C-compatible interface.
03142-048
MASTER
AD5263
R
P
R
P
+5V
SDA
SCL
AD0
5V
5V
5V
AD1
SDA SCL
AD5263
AD0
AD1
SDA SCL
AD5263
AD0
AD1
SDA SCL
AD5263
AD0
AD1
SDA SCL
Figure 49. Multiple AD5263 Devices on One I
2
C Bus
LEVEL SHIFT FOR NEGATIVE VOLTAGE OPERATION
The digital potentiometer is popular in laser diode driver and
certain telecommunication equipment level-setting applications.
These applications are sometimes operated between ground and
some negative supply voltage so that the systems can be biased
at round to avoid large bypass capacitors that may significantly
impede the ac performance. Like most digital potentiometers, the
AD5263 can be configured with a negative supply (see Figure 50).
03142-050
SDA
GND
V
SS
V
DD
SCL
LEVEL SHIFTED
LEVEL SHIFTED
–5V
AD5263
Figure 50. Biased at Negative Voltage
However, the digital inputs must also be level shifted to allow
proper operation because the ground is referenced to the negative
potential. As a result, Figure 51 shows one implementtation
with a couple of transistors and a few resistors. When V
IN
is
high, Q1 is turned on and its emitter is clamped at one threshold
above ground. This threshold appears at the base of Q2, which
causes Q2 to turn off. In this state, V
OUT
approaches −5 V. W h e n
V
IN
is low, Q1 is turned off and the base of Q2 is pulled low, which
in turn causes Q2 to turn on. In this state, V
OUT
approaches 0 V.
Beware that proper time shifting is also needed for successful
communication with the device.
03142-051
V
IN
V
OUT
–5V
–5V
Q2
2N3906
Q1
2N3906
+5V
0V
–5V
0V
R3
1kΩ
R1
10kΩ
R2
10kΩ
Figure 51. Level Shift for Bipolar Potential Operation
ESD PROTECTION
All digital inputs are protected with a series input resistor and
parallel Zener ESD structures shown in Figure 52 and Figure 53.
This protection applies to digital input pins SDI/SDA, CLK/SCL,
CS
/AD0,
RES
/AD1, and
SHDN
.
LOGIC
340Ω
V
SS
03142-052
Figure 52. ESD Protection of Digital Pins
03142-053
A,B,W
V
SS
Figure 53. ESD Protection of Resistor Terminals
TERMINAL VOLTAGE OPERATING RANGE
The AD5263 positive V
DD
and negative V
SS
power supply defines
the boundary conditions for proper 3-terminal digital
potentiometer operation. Supply signals present on the A, B,
and W terminals that exceed V
DD
or V
SS
are clamped by the
internal forward-biased diodes shown in Figure 54.
A
V
DD
B
W
V
SS
03142-054
Figure 54. Maximum Terminal Voltages Set by V
DD
and V
SS
POWER-UP SEQUENCE
Because the ESD protection diodes limit the voltage compliance
at the A, B, and W terminals (see Figure 54), it is important to
power V
DD
and V
SS
before applying any voltage to the A, B, and
W terminals; otherwise, the diodes are forward biased such that
V
DD
and V
SS
are powered unintentionally and may affect the rest
of the circuit. The ideal power-up sequence is in the following
order: GND, V
DD
, V
SS
, V
L
, digital inputs, and V
A/B/W
. The relative
order of powering V
A
, V
B
, V
W
, and digital inputs is not important as
long as they are powered after V
DD
and V
SS
.