Data Sheet

Figure 3-6. Obtaining HeartBeat Pulses with a Pull-up Resistor (SOT23-6)

OUT

VDD

SNSK

SNS

SYNC/MODE

VSS

VDD

HeartBeat" Pulse

If the sensor is wired to a microcontroller as shown in Figure 3-7, the microcontroller can reconfigure the

load resistor to either Vss or Vdd depending on the output state of the QT1011, so that the pulses are

evident in either state.

Figure 3-7. Using a Microcontroller to Obtain HeartBeat Pulses in Either Output State (SOT23-6)

OUT

SNSK

SNS

SYNC/MODE

Microcontroller

Port_M.x

Port_M.y

Electromechanical devices like relays will usually ignore the short HeartBeat pulse. The pulse also has

too low a duty cycle to visibly affect LEDs. It can be filtered completely if desired, by adding an RC filter to

the output, or if interfacing directly and only to a high-impedance CMOS input, by doing nothing or at

most adding a small noncritical capacitor from OUT to Vss.

3.9.3 Output Drive

The OUT pin is active high and can sink or source up to 2 mA. When a large value of Cs (>20 nF) is

used, the OUT current should be limited to <1 mA to prevent gain-shifting side effects, which happen

when the load current creates voltage drops on the die and bonding wires; these small shifts can

materially influence the signal level to cause detection instability.

AT42QT1011

Datasheet

DS40001947A-page 14