MAX1220_12 Datasheet, PDF (37/43 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
DOUT
EOC
CONVERSION BYTE #1
NOP
ACQUISITION #1
MSB1
CONVERSION BYTE #2
NOP
CONVERSION #1
ACQUISITION #2
CONVERSION
CONVERSION #2
LSB1
MSB2
Figure 9a. Clock Mode 11—Externally Timed Acquisition, Sampling and Conversion without CNVST for Maximum ADC Throughput
DIN
CS
SCLK
DOUT
EOC
CONVERSION BYTE
NOP
ACQUISITION
MSB1
NOP
CONVERSION
LSB1
Figure 9b. Clock Mode 11—Externally Timed Acquisition, Sampling and Conversion without CNVST to Reduce Analog Power
Dissipation
If reference mode 00 is requested, or if an external ref-
erence is selected but a temperature measurement is
being requested, wait 45µs with CS high after writing
the conversion byte to extend the acquisition and allow
the internal reference to power up. To perform a tem-
perature measurement, write 24 bytes (192 cycles) of
zeros after the conversion byte using 8-bit NOP com-
mands each framed by CS (to match production test
method; other length NOP sequences are not produc-
tion tested). The temperature result appears on DOUT
during the last 2 bytes of the 192 cycles. For tempera-
ture conversion in clock mode 11 with the TEMP bit set
in the conversion register, no scanning of AIN0 to
AIN15 is performed. Therefore, the CHSEL[3:0] bits are
don’t cares. These bits can be set to 0000b. When the
conversion is complete, only the temperature data is
available.
Conversion-Time Calculations
The conversion time for each scan is based on a num-
ber of different factors: conversion time per sample,
samples per result, results per scan, if a temperature
measurement is requested, and if the external refer-
ence is in use. Use the following formula to calculate
the total conversion time for an internally timed conver-
sion in clock mode 00 and 10 (see the Electrical
Characteristics, as applicable):
Total conversion time =
t_CONV x n_AVG x n_SCAN + t_TS + t_INT-REF,SU
where:
t_CONV = t_DOV, where t_DOV is dependent on the clock
mode and the reference mode selected
n_AVG = samples per result (amount of averaging)
n_SCAN = number of times each channel is scanned; set
to one unless [SCAN1, SCAN0] = 10
t_TS = time required for temperature measurement
(53.1µs); set to zero if temperature measurement is not
requested
t_INT-REF,SU = t_WU (external-reference wake-up); if a
conversion using the external reference is requested
In clock mode 01, the total conversion time depends on
how long CNVST is held low or high. Conversion time in
externally clocked mode (CKSEL1, CKSEL0 = 11)
depends on the SCLK period and how long CS is held
high between each set of eight SCLK cycles. In clock
mode 01, the total conversion time does not include the
time required to turn on the internal reference.
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