1 Introduction

A key parameter when using the DS2X0DF810 25-28G retimers is the temperature lock range (TLR) of the device. The TLR refers to the CDR stay-in-lock ambient temperature range that can be supported without any loss-of-lock event. In the data sheet, TLR is specified in the Electrical Characteristics in terms of both TEMP_LOCK– (maximum temperature change when ramping down below the initial CDR lock acquisition ambient temperature) and TEMP_LOCK+ (maximum temperature change when ramping up above the initial CDR lock acquisition ambient temperature).

The DS2X0DF810 25-28G retimers offer a method through I2C programming to extend the TLR to approximately 150°C (typical) in applications where the device junction temperature may vary beyond the default TLR range mentioned in the DS2X0DF810 data sheet. This is made possible by reading back the internal junction temperature through an on-die temperature sensor and then configuring the CDR loop filter control voltage accordingly. This method allows for the maximum change in the loop filter control voltage to tolerate all supported temperature scenarios, including worst-case scenarios when the device locks at extreme temperatures such as –40°C ambient or 110°C junction temperature.

This application note addresses the I2C programming procedure regarding how to read back the junction temperature and how to extend the device TLR based on the junction temperature readback.