AD5121 datasheet(29/32 Pages) AD

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Data Sheet

AD5121/AD5141

Rev. 0 | Page 29 of 32

TERMINAL VOLTAGE OPERATING RANGE

The AD5121/AD5141 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.

VDD

VSS

Figure 44. Maximum Terminal Voltages Set by VDD and VSS

POWER-UP SEQUENCE

Because there are diodes to limit the voltage compliance at

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

important to power up VDD first before applying any voltage to

Terminal A, Terminal 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 VLOGIC 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 equivalent 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 AD5121/AD5141.

AD5121/

AD5141

VDD VLOGIC

VDD

0.1µF

10µF

0.1µF

10µF

VSS

VLOGIC

0.1µF

10µF

GND

Figure 45. Power Supply Bypassing

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