DA1641.004

1 February, 2019

1 (14)

MAS1641

Capacitance Change Detection with Piezo Alarm

• Adjustable Capacitance Sensing

Range and Alarm Threshold

• Very Low Power Consumption

• 3x Charge Pump

• Self-Drive Type Piezo Driver

• Up to 18Vpp Output Piezo Drive

from 3V Supply

• High Efficiency

• Solution without Inductors

DESCRIPTION

MAS1641 is a single chip system for capacitance

change detection with piezo alarm function. It is an

ideal solution for capacitive infusion and other liquid

level change detection and alarm systems. Either

capacitance

decrease

or

increase

is

detected

depending on change direction selection input (DSEL).

DSEL=GND

chooses

the

capacitance

decrease

detection and DSEL=VIN chooses the capacitance

increase detection.

The system is configurable with three external

resistors.

The

resistor

sets

system

clock

frequency which runs the control unit events and their

oscillator frequency in reference and monitoring

measurements

of

capacitance.

The

reference

measurement is done only once but the monitoring

sensed capacitance and amount of capacitance

decrease (DSEL=GND) or increase (DSEL=VIN) which

is needed to trigger the alarm.

The MAS1641 is turned on just by connecting the

supply

voltage.

An

internal

undervoltage-lockout

(UVLO) circuit allows the device to turn on only if the

supply voltage exceeds 2.1V typ. Also the UVLO circuit

turns off the device if the supply voltage drops below

2.0V typ after the power up.

After power up the device gives a beep signal to the

piezo to indicate it has been turned on. After 4.2s delay

there is done reference capacitance measurement.

This is done by counting pulses from the measurement

oscillator which frequency is defined by resistors

connected to path from RREF pin to GND. Next there

is started a loop where monitored capacitance is

measured periodically using the oscillator which

frequency is defined by resistors connected to path

from MON pin to GND. Monitoring measurements are

run nominally once in two seconds to minimize the

current consumption. Alarm is triggered when the

monitoring measurement count value crosses the

reference measurement count value.

In the alarm the charge pump turned on and an

intermittent (0.2s ON, 1.8s OFF) alarm sound signal is

driven to the piezo. The alarm can be turned off only by

switching off the supplies.

The piezo driver is suitable for driving self-drive type

piezoelectric sounder or diaphragm. It has two outputs

(VOB, VOS) and one feedback input (FEED) to drive 3-

terminal self-drive type piezo in bridge tied load (BTL)

configuration. The piezo driver can drive outputs up to

18Vpp from 3V supply since it is supplied from an

internal 3x charge pump that generates boosted 9V

supply voltage.

The charge pump switches at 1MHz, allowing to using

as

small as

100nF

external

flying

and

output

capacitors.

The MAS1641 is available in a small 3x3x0.75 mm size

QFN-16 package.

FEATURES

APPLICATIONS

• Thin 3x3x0.75 mm QFN-16 package

• Adjustable Sensing Range and Alarm Threshold

• Very Low Power consumption

• 3x Charge Pump with 1MHz Switching Frequency

• Self-Drive Type Piezo Driver

• High Efficiency

• Inductorless Low EMI Solution

• Infusion liquid level drop detection and alarm

• Capacitive water leakage detection and alarm

• Capacitance change detection and alarm