TMS320F280049C: DAC为什么不能输出3.3V

如下DAC代码，目标是让DAC输出3.3V，但是DAC的输出只有3V，请问是为什么？

DAC_setReferenceVoltage(OUTPUT_CURR_DAC_INSTANCE, DAC_REF_VDAC);
DAC_setGainMode(OUTPUT_CURR_DAC_INSTANCE, DAC_GAIN_TWO);
DAC_setLoadMode(OUTPUT_CURR_DAC_INSTANCE, DAC_LOAD_SYSCLK);
DAC_enableOutput(OUTPUT_CURR_DAC_INSTANCE);
OutputValueWithDAC_2(OUTPUT_CURR_DAC_INSTANCE, 4095);