Datasheet

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APPLICATION INFORMATION
AVERAGING
QSPI™ INTERFACE
R/C
BUSY
SDATA
DATACLK
CS
EXT/INT
BYTE
PCS0/SS
MOSI
SCK
QSPI ADS8506
Convert Pulse
CPOL = 0 (Inactive State is LOW)
CPHA = 1 (Data Valid on Falling Edge)
QSPI Port is in Slave Mode
The ADC is the SPI master
SPI™ INTERFACE
ADS8506
SLAS484B – SEPTEMBER 2007 – REVISED DECEMBER 2007
The noise of the converter can be compensated by averaging the digital codes. By averaging conversion results,
transition noise is reduced by a factor of 1/ √ Hz where n is the number of averages. For example, averaging four
conversion results reduces the TN by to 0.4 LSBs. Averaging should only be used for input signals with
frequencies near DC.
For AC signals, a digital filter can be used to low-pass filter and decimate the output codes. This works in a
similar manner to averaging: for every decimation by 2, the signal-to-noise ratio improves 3 dB.
Figure 48 shows a simple interface between the ADS8506 and any QSPI equipped microcontroller. This interface
assumes that the convert pulse does not originate from the microcontroller and that the ADS8506 is the only
serial peripheral.
Figure 48. QSPI Interface to the ADS8506
Before enabling the QSPI interface, the microcontroller must be configured to monitor the slave select line. When
a transition from high to low occurs on slave select ( SS) from BUSY (indicating the end of the current
conversion), the port can be enabled. If this is not done, the microcontroller and the A/D converter may be
out-of-sync.
The SPI interface is generally only capable of 8-bit data transfers. For some microcontrollers with SPI interfaces,
it might be possible to receive data in a similar manner as shown for the QSPI interface in Figure 48 . The
microcontroller needs to fetch the 8 most significant bits before the contents are overwritten by the least
significant bits.
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