MAX1220 Datasheet, PDF(37/47 Page) Maxim Integrated Products – 12-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

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MAX1220 Datasheet, PDF (37/47 Pages) Maxim Integrated Products – 12-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

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12-Bit, Multichannel ADCs/DACs with FIFO,

Temperature Sensing, and GPIO Ports

DIN

SCLK

(CONVERSION BYTE)

(ACQUISITION1)

(CONVERSION1)

(ACQUISITION2)

DOUT

MSB1

LSB1

MSB2

EOC

X = DON'T CARE.

Figure 9. Clock Mode 11âExternally Timed Acquisition, Sampling, and Conversion without CNVST

Externally Clocked Acquisitions and

Conversions Using the Serial Interface

ADC Conversions in Clock Mode 11

In clock mode 11, acquisitions and conversions are ini-

tiated by writing a command byte to the conversion

as the conversion clock. Scanning, averaging and the

FIFO are disabled, and the conversion result is avail-

able at DOUT during the conversion. Output data is

updated on the rising edge of SCLK in clock mode 11.

See Figure 9 for clock mode 11 timing.

Initiate a conversion by writing a command byte to the

conversion register followed by 16 SCLK cycles. If CS

is pulsed high between the eighth and ninth cycles, the

pulse width must be less than 100Âµs. To continuously

convert at 16 cycles per conversion, alternate 1 byte of

zeros (NOP byte) between each conversion byte. If 2

NOP bytes follow a conversion byte, the analog cells

power down at the end of the second NOP. Set the

FBGON bit to one in the reset register to keep the inter-

nal bias block powered.

If reference mode 00 is requested, or if an external refer-

ence is selected but a temperature measurement is being

requested, wait 45Âµs with CS high after writing the con-

version byte to extend the acquisition and allow the inter-

nal reference to power up. To perform a temperature

measurement, write 24 bytes (192 cycles) of zeros after

the conversion byte. The temperature result appears on

DOUT during the last 2 bytes of the 192 cycles.

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 =

tCNV x nAVG x nSCAN + tTS + tINT-REF,SU

where:

tCNV = tDOV, where tDOV is dependent on the clock

mode and the reference mode selected

nAVG = samples per result (amount of averaging)

nSCAN = number of times each channel is scanned; set

to one unless [SCAN1, SCAN0] = 10

tTS = time required for temperature measurement

(53.1Âµs); set to zero if temperature measurement is not

requested

tINT-REF,SU = tWU (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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