MAX11359A_12 Datasheet, PDF (60/67 Pages) Maxim Integrated Products – 16-Bit Data-Acquisition System with ADC, DAC, UPIOs, RTC, Voltage Monitors, and Temp Sensor

MAX11359A
16-Bit Data-Acquisition System with ADC, DAC,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
Clocking with a CMOS Signal
A CMOS signal can be used to drive 32KIN if it is
divided down. Figure 25 is an example circuit, which
works well.
Input Multiplexer
The mux inputs can range between AGND to AVDD.
However, when the internal temperature sensor is
enabled, AIN1 and AIN2 cannot exceed 0.7V. This
necessitates additional circuitry to divide down the
input signal. See Figure 26 for an example circuit that
divides down backlight V_DD to work properly with the
AIN1 pin.
Optical Reflectometry Application with
Dual LED and Single Photodiode
Figure 27 illustrates the MAX11359A in a complete opti-
cal reflectometry application with two transmitting LEDs
and one receiving photodiode. The LEDs transmit light
at a specific wavelength onto the sample strip, and the
photodiode receives the reflections from the strip. Set
the DAC to provide appropriate bias currents for the
LEDs. Always keep the photodiodes reverse-biased or
zero-biased. SPDT1 and SPDT2 switch between the
two LEDs.
Electrochemical Sensor Operation
The MAX11359A family interfaces with electrochemical
sensors. The 10-bit DAC with the force-sense buffers
have the flexibility to connect to many different types of
sensors. An external precision resistor completes the
transimpedance amplifier configuration to convert the
current generated by the sensor to a voltage measure-
ment using the ADC. The induced error from this source
is negligible due to FBA’s extremely low input bias cur-
rent. Internally, the ADC can differentially measure
directly across the external transimpedance resistor,
RF, eliminating any errors due to voltages drifting over
time, temperature, or supply voltage.
Temperature Measurement with
Two Remote Sensors
Use two diode-connected 2N3904 transistors for exter-
nal temperature sensing in Figure 28. Select AIN1 and
AIN2 through the positive and negative mux, respec-
tively. For internal temperature sensor measurements,
set MUXP<3:0> to 0111, and set MUXN<3:0> to 0000.
The analog input signals feed through a PGA to the
ADC for conversion.
Programmable-Gain Instrumentation
Amplifier
Use two op amps and two SPDT switches to implement
a programmable-gain instrumentation amplifier as
shown in Figure 29.
PWM Applications
The MAX11359A integrated PWM is available for LCD bias
control, sensor-bias voltage trimming, buzzer drive, and
duty-cycled sleep-mode power-control schemes. Figure
30 shows the MAX11359A performing LCD bias control.
A sensor-bias voltage trimming application is shown in
Figure 31. Figures 33 and 34 show the PWM circuitry
being used in a single-ended and differential piezo-
electric buzzer-driving application.
ADC Calibration
Internal to the MAX11359A, the ADC is 24 bits and is
always in bipolar mode. The OFFSET CAL and GAIN
CAL data are also 24 bits. The conversion to unipolar
and the gain are performed digitally. The default values
for the OFFSET CAL and GAIN CAL registers in the
MAX11359A are 00 0000h and 80 0000h, respectively.
CMOS CLOCK
(0 TO V_DVDD)
100kΩ
100kΩ
32KIN
MAX11359A
Figure 25. Clocking with a CMOS Signal
60
V_BATT1
V_BATT2
BACKLIGHT
V_DD
GPIOn
UPIO1
MAX11359A
x2
BATTVCHECK
AIN1
V_REF = 1.25V
< 0.6125V
NOTE:
GPIOn IS LOW = LED ON,
HIGH-Z = LED OFF
µP
Figure 26. Input Multiplexer
Maxim Integrated