MAX1220_12 Datasheet, PDF (18/43 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
Detailed Description
The MAX1220/MAX1257/MAX1258 integrate a 12-bit,
multichannel, analog-to-digital converter (ADC), and a
12-bit, octal, digital-to-analog converter (DAC) in a sin-
gle IC. These devices also include a temperature sen-
sor and configurable GPIOs with a 25MHz
SPI-/QSPI-/MICROWIRE-compatible serial interface.
The ADC is available in 8 and 16 input-channel
versions. The octal DAC outputs settle within 2.0µs, and
the ADC has a 225ksps conversion rate.
All devices include an internal reference (2.5V or
4.096V) providing a well-regulated, low-noise reference
for both the ADC and DAC. Programmable reference
modes for the ADC and DAC allow the use of an inter-
nal reference, an external reference, or a combination
of both. Features such as an internal ±1°C accurate
temperature sensor, FIFO, scan modes, programmable
internal or external clock modes, data averaging, and
AutoShutdown allow users to minimize both power con-
sumption and processor requirements. The low glitch
energy (4nV•s) and low digital feedthrough (0.5nV•s) of
the integrated octal DACs make these devices ideal for
digital control of fast-response closed-loop systems.
These devices are guaranteed to operate with a supply
voltage from +2.7V to +3.6V (MAX1257) and from
+4.75V to +5.25V (MAX1220/MAX1258). These devices
consume 2.5mA at 225ksps throughput, only 22µA at
1ksps throughput, and under 0.2µA in the shutdown
mode. The MAX1257/MAX1258 feature 12 GPIOs while
the MAX1220 offers four GPIOs that can be configured
as inputs or outputs.
Figure 1 shows the MAX1257/MAX1258 functional dia-
gram. The MAX1220 only includes the GPIOA0,
GPIOA1 and GPIOC0, GPIOC1 block. The output-con-
ditioning circuitry takes the internal parallel data bus
and converts it to a serial data format at DOUT, with the
appropriate wake-up timing. The arithmetic logic unit
(ALU) performs the averaging function.
SPI-Compatible Serial Interface
The MAX1220/MAX1257/MAX1258 feature a serial inter-
face that is compatible with SPI and MICROWIRE
devices. For SPI, ensure the SPI bus master (typically a
microcontroller (µC)) runs in master mode so that it
generates the serial clock signal. Select the SCLK fre-
quency of 25MHz or less, and set the clock polarity
(CPOL) and phase (CPHA) in the µC control registers to
the same value. The MAX1220/MAX1257/MAX1258
operate with SCLK idling high or low, and thus operate
with CPOL = CPHA = 0 or CPOL = CPHA = 1. Set CS
low to latch any input data at DIN on the falling edge of
SCLK. Output data at DOUT is updated on the falling
edge of SCLK in clock modes 00, 01, and 10. Output
data at DOUT is updated on the rising edge of SCLK in
clock mode 11. See Figures 6–11. Bipolar true-differen-
tial results and temperature-sensor results are available
in two’s complement format, while all other results are in
binary.
A high-to-low transition on CS initiates the data-input
operation. Serial communications to the ADC always
begin with an 8-bit command byte (MSB first) loaded
from DIN. The command byte and the subsequent data
bytes are clocked from DIN into the serial interface on
the falling edge of SCLK. The serial-interface and fast-
interface circuitry is common to the ADC, DAC, and
GPIO sections. The content of the command byte
determines whether the SPI port should expect 8, 16, or
24 bits and whether the data is intended for the ADC,
DAC, or GPIOs (if applicable). See Table 1. Driving CS
high resets the serial interface.
The conversion register controls ADC channel selec-
tion, ADC scan mode, and temperature-measurement
requests. See Table 4 for information on writing to the
conversion register. The setup register controls the
clock mode, reference, and unipolar/bipolar ADC con-
figuration. Use a second byte, following the first, to
write to the unipolar-mode or bipolar-mode registers.
See Table 5 for details of the setup register and see
Tables 6, 7, and 8 for setting the unipolar- and bipolar-
mode registers. Hold CS low between the command
byte and the second and third byte. The ADC averag-
ing register is specific to the ADC. See Table 9 to
address that register. Table 11 shows the details of the
reset register.
Begin a write to the DAC by writing 0001XXXX as a
command byte. The last 4 bits of this command byte
are don’t-care bits. Write another 2 bytes (holding CS
low) to the DAC interface register following the com-
mand byte to select the appropriate DAC and the data
to be written to it. See the DAC Serial Interface section
and Tables 10, 20, and 21.
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