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LMK04826: HOLDOVER function

Intellectual 450 points

Replies: 2

Views: 37

Part Number: LMK04826


My customer has set the LMK04826 for HOLDOVER as shown below.

  - 0x14D00, 0x14EC0, 0x14F7F, 0x15005

The customer has set HOLDOVER_EN = 1 and HOLDOVER_VTUNE_DET = 1, but the both DAC_TRIP_LOW and HIGH registers are not set, so they are all 0.

 In this case, how does HOLDOVER function work ?


When the customer uses the above setting and the CLKin1 manual setting of CLKin_SEL_MODE, can the CLKin path be changed automatically by the HOLDOVER function ?



  • Genius 10640 points

    Hi JH,

    My coworker will get back to you by tomorrow.


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  • Hello JH,

    DAC_TRIP_LOW specifies the voltage from GND where holdover is tripped. So DAC_TRIP_LOW = n means

    Enter holdover if CPout1 voltage > (n + 1) * Vcc / 64

    DAC_TRIP_HIGH specifies the voltage from VCC where holdover is tripped. So DAC_TRIP_HIGH = n means

    Enter holdover if CPout1 voltage < (Vcc - (n + 1) * Vcc / 64)

    In other words, DAC_TRIP_LOW and DAC_TRIP_HIGH at the default values (0) is the most permissive setting with HOLDOVER_VTUNE_DET = 1. The VTUNE_DET holdover trigger will only trip if CPout1 voltage is < Vcc/64 or > Vcc*63/64

    Since CLKin_SEL_MODE is set to "CLKin1 Manual," if a holdover condition is detected the device will switch from CLKin1 to holdover, and when the device leaves holdover it will only switch back to CLKin1. CLKin selection will not be changed unless CLKin_SEL_MODE is set to "auto" mode.


    Derek Payne

    Texas Instruments