VREFH current

[rezrez]

Hi,

I'm using S32K3 MCU and use almost all the ADCs. They are measuring independent inputs. I wonder how much current VREFH pin requires in the worst case. I couldn't find the value in the datasheets or forums.

S32K3 #VREFH

[PavelL]

Hello @rezrez ,

For S32K3 MCUs the ADC reference pin VREFH does not have a specified DC “consumption” current in the datasheet. Instead, VREFH is treated as a high‑impedance reference input that must be driven by a low‑impedance, well‑decoupled source. The datasheet constrains the voltage (VREFH ≤ VDD_HV_A, with only up to +0.1 V RF‑AC headroom) and asks for local decoupling at the pin, but it does not quote a worst‑case mA value.

What matters in practice is the dynamic charge the SAR ADC draws from VREFH during conversions (short transients while the internal capacitor DAC toggles). Because this load is dynamic and depends on resolution, sample rate, and how many ADCs convert concurrently, NXP recommends designing the VREFH supply as a low‑noise, low‑impedance reference with local bulk + ceramic capacitors close to VREFH, rather than sizing to a fixed DC current.

Best regards,

Pavel