MC9S08DN60F1CLF datasheet(189/356 Pages) FREESCALE

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Chapter 10 Analog-to-Digital Converter (S08ADC12V1)

MC9S08DN60 Series Data Sheet, Rev 3

Freescale Semiconductor

189

10.6

Application Information

This section contains information for using the ADC module in applications. The ADC has been designed

to be integrated into a microcontroller for use in embedded control applications requiring an A/D

converter.

10.6.1

External Pins and Routing

The following sections discuss the external pins associated with the ADC module and how they should be

used for best results.

10.6.1.1

Analog Supply Pins

The ADC module has analog power and ground supplies (VDDAD and VSSAD) available as separate pins

on some devices. VSSAD is shared on the same pin as the MCU digital VSS on some devices. On other

devices, VSSAD and VDDAD are shared with the MCU digital supply pins. In these cases, there are separate

pads for the analog supplies bonded to the same pin as the corresponding digital supply so that some degree

of isolation between the supplies is maintained.

When available on a separate pin, both VDDAD and VSSAD must be connected to the same voltage potential

as their corresponding MCU digital supply (VDD and VSS) and must be routed carefully for maximum

noise immunity and bypass capacitors placed as near as possible to the package.

If separate power supplies are used for analog and digital power, the ground connection between these

supplies must be at the VSSAD pin. This should be the only ground connection between these supplies if

possible. The VSSAD pin makes a good single point ground location.

10.6.1.2

Analog Reference Pins

In addition to the analog supplies, the ADC module has connections for two reference voltage inputs. The

high reference is VREFH, which may be shared on the same pin as VDDAD on some devices. The low

reference is VREFL, which may be shared on the same pin as VSSAD on some devices.

When available on a separate pin, VREFH may be connected to the same potential as VDDAD, or may be

driven by an external source between the minimum VDDAD spec and the VDDAD potential (VREFH must

never exceed VDDAD). When available on a separate pin, VREFL must be connected to the same voltage

potential as VSSAD.VREFH and VREFL must be routed carefully for maximum noise immunity and bypass

capacitors placed as near as possible to the package.

AC current in the form of current spikes required to supply charge to the capacitor array at each successive

approximation step is drawn through the VREFH and VREFL loop. The best external component to meet this

current demand is a 0.1

μF capacitor with good high frequency characteristics. This capacitor is connected

between VREFH and VREFL and must be placed as near as possible to the package pins. Resistance in the

path is not recommended because the current causes a voltage drop that could result in conversion errors.

Inductance in this path must be minimum (parasitic only).

MC9S08DN60F1CLF Datasheet(PDF) 189 Page - Freescale Semiconductor, Inc

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