The datasheet says that in ADC PPI (Byte Wide Mode) "...other sample rates supported are 300 kHz, 600 kHz, 900 kHz,
2.4 MHz, and 3.6 MHz".
Is it really the case that 450kHz is not supported or it's just missing from the list? For serial modes 450kHz is supported, and the DECIM_RATE register permits this setting...
Best regards, Istvan