S32K146 conversion frequency

[liuweiliang]

Hello!

IN my application,I needs collect 24 channels of ADC channel. ADC0 14 channels,ADC1 10 channels.I use back to back modes.I use DMA store ADC data.

At present, I have realized the correct collection and transmission of data. I want improve the conversion  rate.In my APP,After the ADC0 channel has completed acquisition, in the DMA interrupt, turn on PDB1 to trigger ADC1 conversion.

I tried to change the trigger time of the PDB. When it is changed to less than 40us, the collected data is incorrect. Will not enter the DMA interrupt.

 

The ADC clock is 48MHz. Sys_CLK is 112MHz.

so how i can improve conversion frequency? IHow to increase the sampling rate to 25Khz?

In s32kxxx datasheet,

so i try continues modes:

1、Software triggered, single channel, continuous mode for transfer suppression.
2、Software trigger, multi-channel ADC channel, when using continuous mode, only the first channel has data, and other channels have no data.
3、PDB hardware trigger, multi-channel ADC channel, does not work when using continuous mode.

[PetrS · Accepted solution]

Hi,

1. ADC sample time should be calculated to keep min value defined in the DS, which is 275ns. So with 48MHZ ADC clock it is 275ns*48MHz = 13.2. So set (14-1) into ADC inspector's sample time parameter.

2. the PBD timer should be properly set. Did you check what value is calculated for "delayValue"? It was 3, so you completely lost a precision for placing delay for PDB channel 1. So choose prescaler divider = 1 in both PDBs setting. This gives you better result for delayValue. Finaly set proper value for PDB channel 1 delay0 register, based on real ADC conversion time. I used below instructions to set a delay for 9us...

PDB_DRV_SetAdcPreTriggerDelayValue(INST_PDLY0, 1UL, 0UL,(uint32_t) (9*delayValue/PDLY_TIMEOUT));

PDB_DRV_SetAdcPreTriggerDelayValue(INST_PDLY1, 1UL , 0UL , (uint32_t) (9*delayValue/PDLY_TIMEOUT));

3. Start PDB0 after PDB1 is completely set.

See attached hw_init.c I modified to make the example running. For the sequential conversion you are using the DMA1 interrupt is called approx each 30us.

For sure you can start both PDBs at the same time, so conversions can run parallel. Start both PDBs in the DMA0 interrupt which is called later, ADC0 sequence is longer. This way you can get even shorter time for DMA0 interrupt, about 18us. See api_dma.c.

BR, Petr