DA6512.003
2 December, 2016
BLOCK DIAGRAM
VDD
OSC
VDD
MISO
MUX
CLK
OSC
CS
SDA/MOSI
SCL/SCLK
XCS
I2C /
SPI
CC
CR
CONTROL
XSPI
EOC
XCLR
VREG
TEST1
TEST2
VREG
TEST
TEMP
EEPROM
GND
GND
Figure 1. MAS6512 block diagram
FUNCTIONAL DESCRIPTION
MAS6512 can interface both single and dual
capacitance sensors. Single capacitance sensors
should be connected between the CS and the CC
inputs. The second capacitor of a dual capacitance
sensor should be connected between the CR and
the CC inputs.
Trim and calibration coefficients can be stored in
the 256-bit EEPROM memory. In normal mode the
stored trim values for the oscillator frequency, offset
capacitance and gain are automatically read from
the EEPROM memory in the beginning of each
conversion. However by using Trimming control
Register it is also possible to choose taking
trimming values from the trimming registers instead
of EEPROM.
A Capacitance-to-Digital Converter (CDC) converts
the input capacitances into a 16-bit output word
(code). The converter front-end can be configured
either for capacitance difference (CS-CR) or
capacitance ratio (CS-CR)/CS measurement mode.
The ratio mode offers pre-linearization for sensor
signals CS(x) being proportional to ~1/x such as
pressure sensor signals (x=pressure).
To avoid modification of the EEPROM by mistake
there is an EEPROM write enable bit in the
EEPROM Control Register which needs to be set
high (1) before any changes can be done to the
EEPROM.
Converter resolution is selected by the over
sampling ratio (OSR) setting. Higher OSR
corresponds to higher resolution but also longer
conversion time.
MAS6512 has an internal clock oscillator making an
external clock unnecessary. To save power it’s
turned on only when a conversion is running. The
frequency is factory trimmed to 200 kHz using a 6-
bit register. An external clock, connected to the
OSC pin, can however be used when a specific test
mode is chosen. This may be necessary when
measuring larger capacitances which require a
slower clock frequency.
There are two internal 22pF capacitance matrices
connected to the CS and the CR inputs. These
matrices are used for sensor offset calibration and
are programmable in 8-bit steps (86fF/step).
The gain is programmable with 8-bits resolution and
sets the input range for sensor changing
In temperature measurement mode it is necessary
to always use a regulated supply voltage. This is
achieved by enabling an internal 1.8V voltage
regulator. When enabled the internal regulator is
automatically turned on during conversion and off
when conversion has been finished. Note that the
internal regulator should be enabled only in the
temperature measurement mode but kept disabled
during capacitance and VDD monitoring modes.
capacitance C=CS MAX-CS_MIN
MAS6512 includes an internal temperature sensor
for temperature compensation purposes.
.
A
multiplexer in the front-end is used to select the
external capacitive sensor, the internal temperature
sensor or an internal band gap reference voltage in
the VDD level monitoring mode.
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MAS [ MICRO ANALOG SYSTEMS ]
