ad5259 Analog Devices, Inc., ad5259 Datasheet - Page 19

• Manufacturer Part Number: ad5259
• Description: Nonvolatile, I2c-compatible 256-position, Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

ESD PROTECTION OF DIGITAL PINS AND
RESISTOR TERMINALS
The AD5259 V
boundary conditions for proper 3-terminal and digital input
operation. Supply signals present on Terminal A, Terminal B,
and Terminal W that exceed V
internal forward biased ESD protection diodes (see Figure 42).
Digital Input SCL and Digital Input SDA are clamped by ESD
protection diodes with respect to V
Figure 43.
POWER-UP SEQUENCE
Because the ESD protection diodes limit the voltage compliance
at Terminal A, Terminal B, and Terminal W (see Figure 42), it
is important to power GND/V
voltage to Terminal A, Terminal B, and Terminal W; otherwise,
the diode is forward biased, so the V
unintentionally and may affect the user’s circuit. The ideal power-
up sequence is in the following order: GND, V
inputs, and then V
V
they are powered after GND/V
A
, V
B
, V
B
Figure 43. Maximum Terminal Voltages Set by V
Figure 42. Maximum Terminal Voltages Set by V
W
, and the digital inputs is not important as long as
DD
, V
A
, V
LOGIC
B
, V
B
, and GND power supplies define the
W
. The relative order of powering
DD
DD
DD
/V
/V
or GND are clamped by the
LOGIC
LOGIC
DD
LOGIC
and V
and GND as shown in
before applying any
.
V
A
W
B
GND
V
SCL
SDA
GND
DD
LOGIC
LOGIC
DD
LOGIC
DD
, V
are powered
and GND
and GND
LOGIC
, digital
Rev. A | Page 19 of 24
LAYOUT AND POWER SUPPLY BYPASSING
It is good practice to use compact, minimum lead length layout
design. The leads to the inputs should be as direct as possible
with minimum conductor length. Ground paths should have
low resistance and low inductance.
Similarly, it is also good practice to bypass the power supplies
with quality capacitors for optimum stability. Supply leads to
the device should be bypassed with disc or chip ceramic capaci-
tors of 0.01 μF to 0.1 μF. Low ESR 1 μF to 10 μF tantalum or
electrolytic capacitors should also be applied at the supplies to
minimize any transient disturbance and low frequency ripple
(see Figure 44). The digital ground should also be joined
remotely to the analog ground at one point to minimize the
ground bounce.
MULTIPLE DEVICES ON ONE BUS
The AD5259 has two configurable address pins, Pin AD0 and
Pin AD1. The state of these two pins is registered upon power-
up and decoded into a corresponding I
address (see Table 5). This allows up to four devices on the bus
to be written to or read from independently.
EVALUATION BOARD
An evaluation board, with all necessary software, is available
to program the AD5259 from any PC running Windows® 98/
2000/ XP. The graphical user interface, as shown in Figure 45,
is straightforward and easy to use. More detailed information
is available in the board’s user manual.
V
Figure 45. AD5259 Evaluation Board Software
DD
10μF
Figure 44. Power Supply Bypassing
C2
+
0.1μF
C1
V
DD
AD5259
2
C-compatible 7-bit
GND
AD5259