Storing ADC data on FatFS SD Card

Hi,

I had interface MSP430F5529 launchpad with FatFS Sd card. I was trying to store value from ADC into SD card and I found that I cannot store the value on SD Card, unless I do "sprintf" or equivalent printf of the data, only then I was able to store the value on SD card. However, sprintf is expensive command and takes more cycle then ADC output i.e some of the data is lost from ADC in doing sprintf. Is there a better alternative than sprintf or something like if I store raw value and later post process it?

Any help will be highly appreciated.

Thanks