AD5253 datasheet(22/32 Pages) AD

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AD5253/AD5254

Data Sheet

Rev. C | Page 22 of 32

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 for which pull-up

resistors are recommended to minimize the MOSFET cross-

conduction current 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 pulls it low to enable write protection. In

applications in which the device is programmed infrequently,

this allows the part to default to write-protection mode after

any one-time factory programming or field calibration without

using an on-board pull-down resistor. Because there are

protection diodes on all inputs, the 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

The AD5253/AD5254 are equipped with two addressing pins,

AD1 and AD0, that allow up to four AD5253/AD5254 devices

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

SDA

AD1

AD0

MASTER

SCL

SDA

AD1

AD0

SCL

SDA

AD1

AD0

SCL

SDA

AD1

AD0

SCL

AD5253/

AD5254

AD5253/

AD5254

AD5253/

AD5254

AD5253/

AD5254

Figure 37. Multiple AD5253/AD5254 Devices on a Single Bus

In wireless base station smart-antenna systems that require

arrays of digital potentiometers to bias the power amplifiers,

large numbers of AD5253/AD5254 devices 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 38) 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 properly programming the I2C

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

operation allows one of 16 devices to be addressed, provided

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

inputs of the decoders are allowed to change once the operation

of the specified device is completed.

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