AD5259 datasheet(19/24 Pages) AD

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Data Sheet

AD5259

Rev. C | Page 19 of 24

ESD PROTECTION OF DIGITAL PINS AND

RESISTOR TERMINALS

The AD5259 VDD, VLOGIC, and GND power supplies define the

boundary conditions for proper 3-terminal and digital input

operation. Supply signals present on Terminal A, Terminal B,

and Terminal W that exceed VDD or GND are clamped by the

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 VLOGIC and GND as shown in

Figure 43.

GND

VDD

Figure 42. Maximum Terminal Voltages Set by VDD and GND

GND

SCL

SDA

VLOGIC

Figure 43. Maximum Terminal Voltages Set by VLOGIC and GND

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/VDD/VLOGIC before applying any

voltage to Terminal A, Terminal B, and Terminal W; otherwise,

the diode is forward biased, so the VDD and VLOGIC are powered

unintentionally and may affect the user’s circuit. The ideal power-

up sequence is in the following order: GND, VDD, VLOGIC, digital

inputs, and then VA, VB, VW. The relative order of powering

VA, VB, VW, and the digital inputs is not important as long as

they are powered after GND/VDD/VLOGIC.

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.

VDD

GND

VDD

µF

0.1

µF

AD5259

Figure 44. Power Supply Bypassing

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 I2C-compatible 7-bit

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.

Figure 45. AD5259 Evaluation Board Software

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