MAX1258 Maxim Integrated Products, MAX1258 Datasheet - Page 18

• Manufacturer Part Number: MAX1258
• Description: Multichannel ADCs/DACs
• Manufacturer: Maxim Integrated Products

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The MAX1220–MAX1223/MAX1257/MAX1258 integrate
a 12-bit, multichannel, analog-to-digital converter
(ADC), and a 12-bit, octal, digital-to-analog converter
(DAC) in a single IC. These devices also include a tem-
perature sensor and configurable GPIOs with a 25MHz
SPI-/QSPI-/MICROWIRE-compatible serial interface.
The ADC is available in 8/12/16 input-channel
versions. The octal DAC outputs settle within 2.0µs, and
the ADC has a 300ksps 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
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 (MAX1221/MAX1223/
MAX1257) and from +4.75V to +5.25V (MAX1220/
MAX1222/MAX1258). These devices consume 2.5mA
at 300ksps throughput, only 22µA at 1ksps throughput,
and under 0.2µA in the shutdown mode. The MAX1257/
MAX1258 feature 12 GPIOs while the MAX1220/
MAX1221 offer 4 GPIOs that can be configured as
inputs or outputs.
Figure 1 shows the MAX1257/MAX1258 functional dia-
gram. The MAX1220/MAX1221 only include the GPIO
A0, A1, GPIO C0, C1 block. The MAX1222/MAX1223
exclude the GPIOs. The output-conditioning 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.
The MAX1220–MAX1223/MAX1257/MAX1258 feature a
serial interface that is compatible with SPI and
MICROWIRE devices. For SPI, ensure the SPI bus mas-
ter (typically a microcontroller (µC)) runs in master
mode so that it generates the serial clock signal. Select
12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
18
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•
s) and low digital feedthrough (0.5nV
SPI-Compatible Serial Interface
Detailed Description
•
s) of
the SCLK frequency of 25MHz or less, and set the
clock polarity (CPOL) and phase (CPHA) in the µC con-
trol registers to the same value. The MAX1220–
MAX1223/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-differential results and tem-
perature-sensor results are available in two’s comple-
ment 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.