MAX11311 Datasheet, PDF (21/51 Pages) Maxim Integrated Products – PIXI, 12-Port Programmable Mixed-Signal I/O with 12-Bit ADC, 12-Bit DAC, Analog Switches, and GPIO

MAX11311
PIXI, 12-Port Programmable Mixed-Signal I/O with
12-Bit ADC, 12-Bit DAC, Analog Switches, and GPIO
Detailed Description
Functional Overview
The MAX11311 has 12 configurable mixed-signal I/O
ports. Each port is independently configured as a DAC
output, an ADC input, a GPI, a GPO, or an analog switch
terminal. User-controllable parameters are available for
each of those configurations. The device offers one
internal and two external temperature sensors. The serial
interface operates as a SPI Mode 0 interface.
The DAC is used to drive out a voltage defined by the
DAC data register of the DAC-configured ports. The DAC
uses either an internal or external voltage reference. The
selection of the voltage reference is set for all the ports
and cannot be configured on a port-by-port basis.
The ADC converts voltages applied to the ADC-configured
ports. The ADC can operate in single-ended mode or in
differential mode, by which any two ports can form a
differential pair. The port configured as the negative
input of the ADC can be used by more than one differential
ADC input pairs. The ADC uses an internal voltage
reference. In some configurations, the ADC uses the DAC
voltage reference. The ADC voltage reference selection
can be configured on a port-by-port basis.
Interrupts provide the host with the occurrence of user-
selected events through the configuration of an interrupt
mask register.
ADC Operations
The ADC is a 12-bit, low-power, successive approximation
analog-to-digital converter, capable of sampling a single
input at up to 400ksps. The ADC’s conversion rate can be
programmed to 400ksps, 333ksps, 250ksps, or 200ksps.
The default conversion rate setting is 200ksps. Each
ADC-configured port can be programmed for one of four
input voltage ranges: 0V to +10V, -5V to +5V, -10V to 0V,
and 0V to +2.5V. The ADC uses the internal ADC 2.5V
voltage reference, or, in some cases, the DAC voltage
reference. The voltage reference can be selected on a
port-by-port basis.
ADC Control
The ADC can be triggered using an external signal CNVT
or from a control bit. CNVT is active-low and must remain
low for a minimal duration of 0.5µs to trigger a conversion.
Four configurations are available:
• Idle mode (default setting).
• Single sweep mode. The ADC sweeps sequentially the
ADC-configured ports, from the lowest index port to
the highest index port, once CNVT is asserted.
• Single conversion mode. The ADC performs a single
conversion at the current port in the series of ADC-
configured ports when CNVT is asserted.
• Continuous sweep mode. The ADC continuously
sweeps the ADC-configured ports. The CNVT port has
no effect in this mode.
ADC Averaging Function
ADC-configured ports can be configured to average
blocks of 2, 4, 8, 16, 32, 64, or 128 conversion results.
The corresponding ADC data register is updated only
when the averaging is completed, thus decreasing the
throughput proportionally. If the number of samples to
average is modified for a given port, the content of the
ADC data register for that port is cleared before starting
to average the new block of samples.
ADC Mode Change
When users change the ADC active mode (continuous
sweep, single sweep, or single conversion), the ADC data
registers are reset. However, ADC data registers retain
content when the ADC is changed to idle mode.
ADC Configurations
The ADC can operate in single-ended, differential, or
pseudo-differential mode. In single-ended mode, the PIXI
port is the positive input to the ADC while the negative
input is grounded internally (Figure 3). In differential mode
(Figure 4), any pair of PIXI ports can be configured as
inputs to the differential ADC. In pseudo-differential mode
(Figure 5), one PIXI port produces the voltage applied
to the negative input of the ADC while another PIXI port
forms the positive input.
The ADC data format is straight binary in single-ended
mode, and two’s complement in differential and pseudo-
differential modes.
DAC Operations
The MAX11311 uses a 12-bit DAC, which operates at the
rate of 40µs per port. Since up to 12 ports can be configured
in DAC-related modes, the minimum refresh rate per port
is 2.083kHz.
No external component is required to set the offset and
gain of the DAC drivers. The PIXI port driver features a
wide output voltage range of ±10V and high current capability
with dedicated power supplies (AVDDIO, AVSSIO).
The DAC uses either the internal or external voltage reference.
Unlike the ADC, the DAC voltage reference cannot be
configured on a port-by-port basis. DAC mode configuration
is illustrated in Figure 6.
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