AN3216 datasheet(8/33 Pages) STMICROELECTRONICS

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Power supplies

AN3216

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DocID17496 Rev 7

2.1.1

Independent A/D converter supply and reference voltage

To improve conversion accuracy, the ADC and the DAC have an independent power supply

that can be filtered separately, and shielded from noise on the PCB.

•

The ADC voltage supply input is available on a separate VDDA pin

•

An isolated supply ground connection is provided on the VSSA pin

VDDA and VREF require a stable voltage. The consumption on VDDA can reach several mA

(see IDD(ADCx), IDD(DAC), IDD(COMPx), IVDDA, and IVREF in the product datasheets for

further information).

When available (depending on the package), VREF¨ must be tied to VSSA.

On BGA 64-pin and all 100-pin or more packages

To ensure a better accuracy on low-voltage inputs and outputs, the user can connect to

VREF+, a separate external reference voltage which is lower than VDD. VREF+ is the highest

voltage, represented by the full scale value, for an analog input (ADC) or output (DAC)

signal.

•

For ADC

–

2.4 V

≤ VREF+ = VDDA for full speed (ADCCLK = 16 MHz, 1 Msps)

–

1.8 V

≤ VREF+ = VDDA for medium speed (ADCCLK = 8 MHz, 500 Ksps)

–

2.4 V

≤ VREF+ ≠ VDDA for medium speed (ADCCLK = 8 MHz, 500 Ksps)

–

1.8 V

≤ VREF+ < VDDA for low speed (ADCCLK = 4 MHz, 250 Ksps)

–

When product voltage range 3 is selected (VCORE = 1.2 V), the ADC is low speed

(ADCCLK = 4 MHz, 250 Ksps)

•

For DAC

–

1.8 V

≤ VREF+ < VDDA

On packages with 64 pins or less (except BGA package)

VREF+ and VREF- pins are not available. They are internally connected to the ADC voltage

supply (VDDA) and ground (VSSA).

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