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LT3580 Switching Frequency not matching the datasheet.

I'm currently doing some EMI-EMC measurements and have used the IC LT3580 as a boost converter and used the same component value as the DC 1144A-A eval board. But using RT as said in the eval board which is 82.4KOhm that should provide a switching frequency of around 1MHz for my measurement it only gives around 440KHz switching frequency.  Can you please help me debug this? 

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  • Ensure R8 is populated so the SYNC pin is low. Ensure the input voltage is between 3V and 10V and isn't isn't dipping lower (supply is not current limited). Ensure the Rt pin to GND resistance is close to the desired value of 84.5K. Other than that, ensure solder joints are good. If everything looks good, try a new IC but that is not likely to be the issue.