TMS320F28379D: TMS320F28379D: How to Determine the ADC Acquisition window for Current Sensor

SOumitri Kumar Suraparaju

Hello Forms,

I have Current Sensor, which has a range from -700A to +700A range which is operated at 5V range using a divider I convert that into 3V range.

When reading the Current Value at "0A" ADC values are being Varied around 2038 - 2049, Never the Constant (At 715ns Window - From Examples).

How do I calculate acquisition window.

My ADC Clk is 12.5MHz, with 12-bit, Single Ended, where ADC SOC Triggered using ePWM Channels.

Thanks in Advance,
Soumitri kumar

8 months ago

0 Srikanth Yerra 8 months ago

TI__Expert 3120 points

Hi Soumitri

The ADC acquisition window is the time allowed for the ADC's sample-and-hold circuit to charge the sampling capacitor before conversion begins. For the TMS320F28379D, this window is determined by

Key Parameters Affecting Acquisition Window

ACQPS (Acquisition Prescale) bits: Found in the ADCSOCxCTL register
SYSCLK frequency: The system clock frequency
ADC clock divider: Set in ADCCTL2.PRESCALE

Calculation Formula

The acquisition window is calculated as:

Acquisition Window (ns) = (ACQPS + 1) × (ADC clock period)

Where:

ADC clock period = 1/(SYSCLK frequency ÷ ADC clock divider)

Example Calculation

If:

SYSCLK = 200 MHz
ADC clock divider = 16
ACQPS = 14

Then:

ADC clock = 200 MHz ÷ 16 = 12.5 MHz
ADC clock period = 1/12.5 MHz = 80 ns
Acquisition window = (14 + 1) × 80 ns = 1200 ns

In your case of 715ns:

- ACQPS = (715 ns ÷ 80 ns) - 1
- ACQPS = 8.9375 - 1
- ACQPS = 7.9375
Since ACQPS must be an integer, we have two options:
- ACQPS = 7: This gives (7+1) × 80 ns = 640 ns (less than target)
- ACQPS = 8: This gives (8+1) × 80 ns = 720 ns (slightly more than target)

Thanks

Srikanth