AD5253 datasheet(21/28 Pages) AD

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AD5253/AD5254

Rev. 0 | Page 21 of 28

DIGITAL INPUT/OUTPUT CONFIGURATION

SDA is a digital input/output with an open-drain MOSFET that

requires a pull-up resistor for proper communication. On the

other hand, SCL and WP are digital inputs with pull-up

resistors recommended to minimize the MOSFET cross-

conduction when the driving signals are lower than VDD. SCL

and WP have ESD protection diodes, as shown in Figure 35 and

Figure 36.

WP can be permanently tied to VDD without a pull-up resistor if

the write-protect feature is not used. If WP is left floating, an

internal current source will pull it low to enable write-protect.

In applications where the device is not being programmed on a

frequent basis, this allows the part to default to write-protect

after any one-time factory programming or field calibration

without using an on-board pull-down resistor. Since there are

protection diodes on all these inputs, their signal levels must not

be greater than VDD to prevent forward biasing of the diodes.

GND

SCL

VDD

Figure 35. SCL Digital Input

GND

INPUTS

VDD

Figure 36. Equivalent WP Digital Input

MULTIPLE DEVICES ON ONE BUS

AD5253/AD5254 are equipped with two addressing pins, AD1

and AD0, that allow up to four AD5253/AD5254s to be

operated on one I2C bus. To achieve this result, the states of

AD1 and AD0 on each device must first be defined. An example

is shown in Table 12 and Figure 37. In I2C programming, each

device is issued a different slave address—01011(AD1)(AD0)—

to complete the addressing.

Table 12. Multiple Devices Addressing

AD1

AD0

Device Addressed

VDD

+5V

VDD

AD0

AD1

SDA SCL

MASTER

AD0

AD1

SDA SCL

AD0

AD1

SDA SCL

AD0

AD1

SDA

SCL

Figure 37. Multiple AD5253/AD5254s on a Single Bus

In wireless base station smart antenna systems where arrays of

digital potentiometers may be needed to bias the power

amplifiers, large numbers of AD5253/AD5254s can be

addressed by using extra decoders, switches, and I/O buses, as

shown in Figure 38. For example, to communicate to a total of

16 devices, four decoders and 16 sets of combinational switches

(four sets shown in Figure 36) are needed. Two I/O buses serve

as the common inputs of the four 2 × 4 decoders and select four

sets of outputs at each combination. Because the four sets of

combination switch outputs are unique, as shown in Figure 38, a

specific device is addressed by proper I2C programming with

the slave address defined as 01011(AD1)(AD0). This operation

allows one out of 16 devices to be addressed, provided the

inputs of the two decoders do not change states. The decoders’

inputs are allowed to change once the operation of the specified

device is completed.

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