DA6512.000

11 July, 2012

I

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BLOCK DIAGRAM

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.

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

or

Converter resolution is selected by the over

sampling

ratio

(OSR)

setting.

Higher

OSR

corresponds to higher resolution but also longer

conversion time.

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 range for how much the measured

capacitance can change.

MAS6512 includes an internal temperature sensor

for

temperature

compensation

purposes.

A

multiplexer in the front-end is used to select either

the external capacitive sensor or the internal

temperature sensor.

Trim and calibration coefficients can be stored in

the 256-bit EEPROM memory. 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. To avoid modification of the EEPROM

by mistake there is an EEPROM write enable

register which needs to be set to %01010101

EEPROM.

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 trimmed to 200kHz using a 6-bit

register. An external clock, connected to the

OSCOUT pin, can however be used when a specific

test mode is chosen. This might be necessary when

measuring large capacitance since a slower clock

frequency is needed in this case.

MAS6512 includes a 1.8V regulator that can be

disabled in capacitance measurement mode. In

temperature measurement mode the regulator is

always used. The regulator is turned off between

conversions.

Communication with MAS6512 is handled by the

serial

interface

compatible

with

either

a

bi-

directional 2-wire I

XSPI pin is for selecting which bus type is used.

The XCLR pin can be used to reset the device

including the serial communication.

The EOC pin indicates if a conversion has finished

and the result is ready to be read from the memory

via the serial interface.

MISO

SDA/MOSI

SCL/SCLK

MUX

TEMP

∆Σ

CONTROL

I2C /

SPI

EEPROM

CLK

OSC

XCS

XSPI

EOC

XCLR

CS

CC

CR

VDD

GND

GND

VREG

TEST

VREG

TEST1

TEST2

VDD

OSCOUT