DA1641.004
1 February, 2019
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 RCLK resistor sets system clock
frequency which runs the control unit events and their
timing. RCOM and RINC (only in increase detection) or
RDEC (only in decrease detection) resistors adjust
oscillator frequency in reference and monitoring
measurements of capacitance. The reference
measurement is done only once but the monitoring
measurements are run periodically. Together the RCOM
and the RINC or RDEC resistor values define range of
sensed capacitance and amount of capacitance
decrease (DSEL=GND) or increase (DSEL=VIN) which
is needed to trigger the alarm.
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 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.
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.
After power up the device gives a beep signal to the
piezo to indicate it has been turned on. After 4.2s delay
FEATURES
APPLICATIONS
• Thin 3x3x0.75 mm QFN-16 package
• Adjustable Sensing Range and Alarm Threshold
• Very Low Power consumption
• Infusion liquid level drop detection and alarm
• Capacitive water leakage detection and alarm
• Capacitance change detection and alarm
• 3x Charge Pump with 1MHz Switching Frequency
• Self-Drive Type Piezo Driver
• High Efficiency
• Inductorless Low EMI Solution
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