AD5142ABCPZ100-RL7 datasheet(27/29 Pages) AD

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Data Sheet

AD5122A/AD5142A

THEORY OF OPERATION

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Rev. D | 27 of 29

mode, the output voltage is dependent mainly on the ratio of the

internal resistors, RAW and RWB, and not the absolute values.

Therefore, the temperature drift reduces to 5 ppm/°C.

TERMINAL VOLTAGE OPERATING RANGE

The AD5122A/AD5142A are designed with internal ESD diodes

for protection. These diodes also set the voltage boundary of the

terminal operating voltages. Positive signals present on Terminal

A, Terminal B, or Terminal W that exceed VDD are clamped by the

forward-biased diode. There is no polarity constraint between VA,

VW, and VB, but they cannot be higher than VDD or lower than VSS.

Figure 44. Maximum Terminal Voltages Set by VDD and VSS

POWER-UP SEQUENCE

Because there are diodes to limit the voltage compliance at Termi-

nal A, Terminal B, and Terminal W (see Figure 44), it is important to

power up VDD first before applying any voltage to Terminal A, Termi-

nal B, and Terminal W. Otherwise, the diode is forward-biased such

that VDD is powered unintentionally. The ideal power-up sequence

is VSS, VDD, VLOGIC, digital inputs, and VA, VB, and VW. The order

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

as they are powered after VSS, VDD, and VLOGIC. Regardless of

the power-up sequence and the ramp rates of the power supplies,

once VDD is powered, the power-on preset activates, which restores

EEPROM values to the RDAC registers.

LAYOUT AND POWER SUPPLY BIASING

It is always a good practice to use a compact, minimum lead length

layout design. Ensure that the leads to the input are as direct as

possible with a minimum conductor length. Ground paths should

have low resistance and low inductance. It is also good practice to

bypass the power supplies with quality capacitors. Apply low equiv-

alent series resistance (ESR) 1 µF to 10 µF tantalum or electrolytic

capacitors at the supplies to minimize any transient disturbance and

to filter low frequency ripple. Figure 45 illustrates the basic supply

bypassing configuration for the AD5122A/AD5142A.

Figure 45. Power Supply Bypassing

AD5142ABCPZ100-RL7 Datasheet(PDF) 27 Page - Analog Devices