Freescale Semiconductor PXR4030, Reference Manual

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Enhanced Queued Analog-to-Digital Converter (EQADC)
Freescale Semiconductor 27-97
PXR40 Microcontroller Reference Manual, Rev. 1
The ADC conversion speed (in K samples per second - Ksps) is calculated by the following formula. T he
number of sampling cycles is determined by the LST bits in the command message — see Conversion
Command Format for the Standard Configuration — and it can take one of the following values: 2, 8, 64,
or 128 ADC clock cycles. The number of AD conversion cycles is 13 for differential conversions and 14
for single-ended conversions (12 bits resolution and unitary input gain). The maximum conversion speed
is achieved when the ADC Clock frequency is set to its maximum, the number of sampling cycles set to
its minimum (2 cycles), and the resolution is also set to the minimum (8 bits) with input unitary gain.
Table 27-40 shows an example of how the ADC0/1_CLK_PS can be set when using a 120 MHz platform
clock and the corresponding conversion speeds for all possible ADC clock frequencies. The table also
shows that according to the platform clock frequency, certain clock divide factors are invalid (2, 4, 6, 8
clock divide factors in the example) since their use would result in a ADC clock frequency higher than the
maximum one supported by the ADC. In this example, the maximum ADC clock frequency is 15 MHz (12
bits resolution conversions with unitary input gain).
Table 27-40. ADC Clock Configuration Example (Platform Clock Frequency=120 MHz)
ADC0/1_CLK_PS[0:4]
Platform Clock
Divide Factor
ADC Clock
(Platform Clock
= 120 MHz)
Differential
Conversion Speed
with Default Sampling
Time (2 cycles)
Single-Ended
Conversion Speed
with Default Sampling
Time (2 cycles)
0b00000 2 N/A N/A N/A
0b00001 4 N/A N/A N/A
0b00010 6 N/A N/A N/A
0b00011 8 15.0 MHz 1.0 Msps 938 Ksps
0b00100 10 12.0 MHz 800 Ksps 750 Ksps
0b00101 12 10.0 MHz 667 Ksps 625 Ksps
0b00110 14 8.57 MHz 571 Ksps 536 Ksps
0b00111 16 7.5 MHz 500 Ksps 469 Ksps
0b01000 18 6.67 MHz 444 Ksps 417 Ksps
0b01001 20 6.0 MHz 400 Ksps 375 Ksps
0b01010 22 5.45 MHz 364 Ksps 341 Ksps
0b01011 24 5.0 MHz 333 Ksps 313 Ksps
0b01100 26 4.62 MHz 308 Ksps 288 Ksps
0b01101 28 4.29 MHz 286 Ksps 268 Ksps
0b01110 30 4.0 MHz 267 Ksps 250 Ksps
0b01111 32 3.75 MHz 250 Ksps 234 Ksps
0b10000 34 3.53 MHz 235 Ksps 221 Ksps
0b10001 36 3.33 MHz 222 Ksps 208 Ksps
0b10010 38 3.16 MHz 211 Ksps 198 Ksps
0b10011 40 3.0 MHz 200 Ksps 188 Ksps
0b10100 42 2.86 MHz 190 Ksps 179 Ksps
0b10101 44 2.73 MHz 182 Ksps 170 Ksps
ADCConversionSpeed
ADCClockFrequency MHz
 
NumberOfSamplingCycles NumberOfADConversionCycles +
 
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