mc68hc908mr8 Freescale Semiconductor, Inc, mc68hc908mr8 Datasheet - Page 318

• Manufacturer Part Number: mc68hc908mr8
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Analog-to-Digital Converter (ADC)
18.8.2 ADC Voltage In (ADVIN)
18.8.3 ADC External Connection
18.8.3.1 V
18.8.3.2 ANx
18.8.3.3 Grounding
Technical Data
318
REFH
ADVIN is the input voltage signal from one of the seven ADC channels
to the ADC module.
Both ac and dc current are drawn through V
form of current spikes required to supply charge to the capacitor array at
each successive approximation step. The dc current flows through the
internal resistor string. The best external component to meet both these
current demands is a capacitor in the 0.01 µF to 1 µF range with good
high-frequency characteristics. This capacitor is connected between
V
pins. Resistance in the path is not recommended because the dc current
will cause a voltage drop which could result in conversion errors.
Empirical data shows that capacitors from the analog inputs to V
improve ADC performance. 0.01 µF and 0.1 µF capacitors with good
high-frequency characteristics are sufficient. These capacitors must be
placed as close as possible to the package pins.
In cases where separate power supplies are used for analog and digital
power, the ground connection between these supplies should be at the
V
supplies if possible. The V
location.
REFH
SS
pin. This should be the only ground connection between these
and V
Analog-to-Digital Converter (ADC)
SS
and must be placed as close as possible to the package
SS
pin makes a good single-point ground
REFH
MC68HC908MR8 — Rev 4.1
. The ac current is in the
Freescale Semiconductor
RL