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Relieving Supply Chain Issues of the 1-Wire® Silicon Serial Number Chip

Feb 16, 2022

Stewart Merkel  By: Stewart Merkel
 Principal MTS, Applications, Analog Devices 


Two of the most popular long running legacy devices for more than 30 years, the 1-Wire® Silicon Serial Number DS2401 and DS1990A, has suffered supply chain issues. To relieve this issue, Analog Devices has developed the alternatives DS2401A and DS1990AA. These alternatives use a different wafer process that has greatly reduced lead times.

However, since the alternatives use a different wafer process, there are some electrical characteristic differences that require careful examination to know if it is a drop-in replacement. The product engineer can then conclude if hardware or software changes are required for the new alternatives. This blog discusses the differences between the legacy and alternative devices to help the product engineer in this transition.

relieving supply chain issues of the 1-wire silicon serial number chip

Examination of Differences of Concern

In examination, the differences of concern are subtle and for most systems the alternative 1-Wire serial number device can be used with no or minimal changes. However, depending on the implementation, there may be some systems that require HW and/or SW changes. For example, a system may require a hardware change of the pullup resistor (RPUP) to be modified from 5kΩ to 2kΩ in a 5V system and the package type used may need to be changed on the PCB. As well, overvoltage protection components may need to be added. The software's 1-Wire timing may need to change the recovery time (tREC) from 1us to 5us and the system's reset low time (tRSTL) should be verified to not exceed 640us. Table 1 identifies key datasheet parameters and explains how they may impact the system when transitioning from the legacy devices to the alternatives. This does not encompass every conceivable change needed but provides sufficient information to transition most systems.

Table 1. Summary of Differences of Concern

Parameter or  Item DS2401 and DS1990A DS2401A and DS1990AA Impact of Using Alternate Device
Absolute max 7V/6V 6V Absolute max voltage range needs a limited of 6V for DS2401A, DS1990A and DS1990AA. May require a hardware change to limit voltage if DS2401 was used.
VPUPmax 6V 5.25V Operating voltages are not compatible above 5.25V. May require a hardware change to limit voltage.
VPUPmin 2.8V 3V Operating voltages are not compatible below 3V.
May require a hardware change if supply is too low.
RPUPmax 5kΩ 2kΩ A hardware change will be needed if the system used a value greater than 2kohm.
RPUPmin 1.5kΩ 300Ω Should not be an impact to transition.
VIHmin 2.2V *0.75V x VPUP *Only supports typical.
CIO 800pF *1000pF *Has more input capacitance at startup. This could require elongating the power up idle time in software before beginning communication.
tRECmin 1us 5us If tREC is shorter than 5us then a software change is needed.
tRSTLmax 960us 640us If tRSLT is greater than 640us then a software change is needed.
Chip
Packages
All types Reduced Alternative only supports TO-92 and TSOC.  Any other type of packages (i.e., SOT-223, Flip Chip, and WLP) requires a PCB hardware change.
Skip ROM
or
Match ROM
No Response Will respond If a multidrop configuration exists in the application, responses from connected alternative devices should be considered.  For example, if skip ROM is used to communicate to another type of  1-Wire slave on the 1-Wire bus were before DS2401 would not respond, a DS2401A would respond interfering with the other 1-wire slave's return response.

In summary, the information provided should assist the product engineer to quickly identify if changes are needed for their system.