MAX1021 Datasheet, PDF (21/40 Pages) Maxim Integrated Products – 10-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

10-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
Write to the GPIOs by writing a command byte to the
GPIO command register. Write a single data byte to the
MAX1021/MAX1043 following the command byte.
The GPIOs can sink and source current. GPIOA0 and
GPIOA1 can sink and source up to 15mA. GPIOC0 and
GPIOC1 can sink 4mA and source 2mA. See Table 3.
Clock Modes
Internal Clock
The MAX1021/MAX1043 can operate from an internal
oscillator. The internal oscillator is active in clock
modes 00, 01, and 10. Figures 6, 7, and 8 show how to
start an ADC conversion in the three internally timed
conversion modes.
Read out the data at clock speeds up to 25MHz
through the SPI interface.
External Clock
Set CKSEL1 and CKSEL0 in the setup register to 11 to
set up the interface for external clock mode 11. See
Table 5. Pulse SCLK at speeds from 0.1MHz to
3.6MHz. Write to SCLK with a 40% to 60% duty cycle.
The SCLK frequency controls the conversion timing.
See Figure 9 for clock mode 11 timing. See the ADC
Conversions in Clock Mode 11 section.
ADC/DAC References
Address the reference through the setup register, bits 3
and 2. See Table 5. Following a wake-up delay, set
REFSEL[1:0] = 00 to program both the ADC and DAC
for internal reference use. Set REFSEL[1:0] = 10 to pro-
gram the ADC for internal reference. Set REFSEL[1:0] =
10 to program the DAC for external reference, REF1.
When using REF1 or REF2/AIN_ in external-reference
mode, connect a 0.1µF capacitor to AGND. Set
REFSEL[1:0] = 01 to program the ADC and DAC for
external-reference mode. The DAC uses REF1 as its
external reference, while the ADC uses REF2 as its
external reference. Set REFSEL[1:0] = 11 to program
the ADC for external differential-reference mode. REF1
is the positive reference and REF2 is the negative refer-
ence in the ADC external differential mode.
Table 3. GPIO Maximum Sink/Source
Current
CURRENT
GPIOA0, GPIOA1
(mA)
GPIOC0, GPIOC1
(mA)
Sink
15
4
Source
15
2
When REFSEL[1:0] = 00 or 10, REF2/AIN_ functions as
an analog input channel. When REFSEL[1:0] = 01 or 11,
REF2/AIN_ functions as the device’s negative reference.
Temperature Measurements
Issue a command byte setting bit 0 of the conversion
register to one to take a temperature measurement.
See Table 4. The MAX1021/MAX1043 perform tempera-
ture measurements with an internal diode-connected
transistor. The diode bias current changes from 68µA to
4µA to produce a temperature-dependent bias voltage
difference. The second conversion result at 4µA is sub-
tracted from the first at 68µA to calculate a digital value
that is proportional to absolute temperature. The output
data appearing at DOUT is the digital code above,
minus an offset to adjust from Kelvin to Celsius.
The reference voltage used for the temperature mea-
surements is always derived from the internal reference
source to ensure that 1 LSB corresponds to 1/8th of a
degree Celsius. On every scan where a temperature
measurement is requested, the 12-bit temperature con-
version is carried out first. The first 2 bytes of data read
from the FIFO contain the result of the 12-bit tempera-
ture measurement. If another temperature measure-
ment is performed before the first temperature result is
read out, the old measurement is overwritten by the
new result. Temperature results are in degrees Celsius
(two’s complement). See the Applications Information
section for information on how to perform temperature
measurements in each clock mode.
Register Descriptions
The MAX1021/MAX1043 communicate between the
internal registers and the external circuitry through the
SPI-compatible serial interface. Table 1 details the
command byte, the registers, and the bit names.
Tables 4–12 show the various functions within the con-
version register, setup register, unipolar-mode register,
bipolar-mode register, ADC averaging register, DAC
select register, reset register, and GPIO command reg-
ister, respectively.
Conversion Register
Select active analog input channels, scan modes, and
a single temperature measurement per scan by issuing
a command byte to the conversion register. Table 4
details channel selection, the four scan modes, and
how to request a temperature measurement. Start a
scan by writing to the conversion register when in clock
mode 10 or 11, or by applying a low pulse to the
CNVST pin when in clock mode 00 or 01. See Figures 6
and 7 for timing specifications for starting a scan with
CNVST.
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