MAX1221 Datasheet, PDF (35/44 Pages) Maxim Integrated Products – 12-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
DIN
CS
SCLK
(CONVERSION BYTE)
(UP TO 514 INTERNALLY CLOCKED ACQUISITIONS AND CONVERSIONS)
DOUT
EOC
MSB1
t_DOV
LSB1
MSB2
Figure 8. Clock Mode 10—The command byte to the conversion register begins the acquisition (CNVST is not required).
Externally Timed Acquisitions and
Internally Timed Conversions with CNVST
ADC Conversions in Clock Mode 01
In clock mode 01, conversions are requested one at a
time using CNVST and performed automatically using
the internal oscillator. See Figure 7 for clock mode 01
timing after a command byte is issued.
Setting CNVST low begins an acquisition, wakes up the
ADC, and places it in track mode. Hold CNVST low for
at least 1.4µs to complete the acquisition. If reference
mode 00 or 10 is selected, an additional 45µs is
required for the internal reference to power up. If a tem-
perature measurement is being requested, reference
power-up and temperature measurement is internally
timed. In this case, hold CNVST low for at least 40ns.
Set CNVST high to begin a conversion. Sampling is
completed approximately 500ns after CNVST goes high.
After the conversion is complete, the ADC shuts down
and pulls EOC low. EOC stays low until CS or CNVST is
pulled low again. Wait until EOC goes low before pulling
CS or CNVST low. The number of CNVST signals must
equal the number of conversions requested by the scan
and averaging registers to correctly update the FIFO.
Wait until all conversions are complete before reading
the FIFO. SPI communications to the DAC and GPIO
registers are permitted during conversion. However,
coupled noise may result in degraded ADC SNR.
If averaging is turned on, multiple CNVST pulses need to
be performed before a result is written to the FIFO. Once
the proper number of conversions has been performed
to generate an averaged FIFO result (as specified to the
averaging register), the scan logic automatically switch-
es the analog input multiplexer to the next requested
channel. If a temperature measurement is programmed,
it is performed after the first rising edge of CNVST follow-
ing the command byte written to the conversion register.
The temperature-conversion result is available on DOUT
once EOC has been pulled low.
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