Datasheet

V850ES/JG3-H, V850ES/JH3-H CHAPTER 15 A/D CONVERTER

R01UH0042EJ0500 Rev.5.00 Page 709 of 1513

Aug 12, 2011

(7) AVREF0 pin

(a) The AV

REF0 pin is used as the power supply pin of the A/D converter and also supplies power to the alternate-

function ports. In an application where a backup power supply is used, be sure to supply the same potential as

DD to the AVREF0 pin as shown in Figure 15-15.

(b) The AV

REF0 pin is also used as the reference voltage pin of the A/D converter. If the source supplying power to

the AVREF0 pin has a high impedance or if the power supply has a low current supply capability, the reference

voltage may fluctuate due to the current that flows during conversion (especially, immediately after the

conversion operation enable bit ADA0CE has been set to 1). As a result, the conversion accuracy may drop.

To avoid this, it is recommended to connect a capacitor across the AV

REF0 and AVSS pins to suppress the

reference voltage fluctuation as shown in Figure 15-15.

REF0 pin has a high DC resistance (for example, because of insertion of

a diode), the voltage when conversion is enabled may be lower than the voltage when conversion is stopped,

because of a voltage drop caused by the A/D conversion current.

Figure 15-15. AV

REF0 Pin Processing Example

REF0

Note

Main power supply

Note Parasitic inductance

(8) Reading ADA0CRn register

When the ADA0M0 to ADA0M2, ADA0S, ADA0PFM, or ADA0PFT register is written, the contents of the ADA0CRn

ADA0M0 to ADA0M2, ADA0S, ADA0PFM, or ADA0PFT register. Also, when an external/timer trigger is

acknowledged, the contents of the ADA0CRn register may be undefined. Read the conversion result after

completion of conversion and before the next external/timer trigger is acknowledged. The correct conversion result

may not be read at a timing different from the above.

(9) External trigger mode

When using the external trigger mode, the input trigger during A/D conversion will not be acknowledged.