Datasheet

Figure 3-10. Auto-off Delay, Active Low Output

Vm = Vss (delay multiplier = x1)

Example using a chart to calculate Rt and Ct

Requirements:

• Active low output (Vop connected to VSS)

• Auto-off delay 25 minutes

• VDD = 4 V

1. Calculate Auto-off delay in seconds 25 × 60 = 1500.

2. Find

1500

= 1500 on the 4 V chart in Figure 3-10.

3. This shows the following suitable Ct / Rt combinations:

– 100 nF / 20 kΩ

– 47 nF / 40 kΩ

– 22 nF / 90 kΩ

– 10 nF / 190 kΩ

Note: The Auto-off delay times shown are nominal and will vary from chip to chip and with

capacitor and resistor tolerance.

3.11.5 Auto-off – Overriding the Auto-off Delay

In normal operation the QT1012 output is turned off automatically after the auto-off delay. In some

applications it may be useful to extend the auto-off delay (“sustain” function) or to switch the output off

immediately (“cancel” function). This can be achieved by pulsing the voltage on the delay multiplier

resistor Rm as shown in Figure 3-11 and Figure 3-12 on page 18.

AT42QT1012

Datasheet

DS40001948A-page 18