MCF5253VM140J Freescale Semiconductor, MCF5253VM140J Datasheet - Page 197

• Manufacturer Part Number: MCF5253VM140J
• Description: IC MCU 2.1MIPS 140MHZ 225MAPBGA
• Manufacturer: Freescale Semiconductor
• Series: MCF525xr

Specifications of MCF5253VM140J

• Core Processor: Coldfire V2
• Core Size: 32-Bit
• Speed: 140MHz
• Connectivity: CAN, EBI/EMI, I²C, QSPI, UART/USART, USB OTG
• Peripherals: DMA, WDT
• Program Memory Type: ROMless
• Ram Size: 128K x 8
• Voltage - Supply (vcc/vdd): 1.08 V ~ 1.32 V
• Data Converters: A/D 6x12b
• Oscillator Type: External
• Operating Temperature: -20°C ~ 70°C
• Package / Case: 225-MAPBGA
• Processor Series: MCF525x
• Core: ColdFire V2
• 3rd Party Development Tools: JLINK-CF-BDM26, EWCF
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Number Of I /o: -
• Eeprom Size: -
• Program Memory Size: -
• Lead Free Status / Rohs Status: Details

the comparator will have difficulty determining if the result is negative or positive. The circuit becomes
sensitive to noise. Therefore, we recommend to set K between 20 and 50.
The ADCCLOCK should be such that the comparator can take the decision whether its output needs to be
positive or negative in time t.
When K is high it means that RC is high relative to the clock period of the ADC and the voltage step over
C per clock cycle becomes small. Therefore, the ADC becomes slow in responding to changes of the input
voltage and this affects the accuracy of the measurement.
For a correct measurement, the voltage over C should be equal to the input voltage during the entire
measurement cycle (1024 ADC clocks). Therefore for the first conversion or when switching channels,
two consecutive measurements should be made and the first one ignored. This then allows the capacitor
(C) to charge to the average value of the channel. If voltages between the channels are significantly
different, the first measurement will be inaccurate because the capacitor may not have charged to the new
level in time. When reading the same channel, it is not necessary to ignore every other measurement.
We therefore recommend to use R = 33kΩ, C = 10nF with ADCLK = BUSCLK/256. This should produce
good results for typical system clock frequencies between 30 MHz and 70 MHz.
Freescale Semiconductor
MCF5253 Reference Manual, Rev. 1
t
=
---------------------------------- -
ADCCLOCK
1
Analog to Digital Converter (ADC)
Eqn. 12-2
12-5