AT42QT1012_10 Datasheet, PDF (16/28 Pages) ATMEL Corporation – One-channel Toggle-mode Touch Sensor IC with Power Management Functions

Figure 3-10. Auto-off Delay, Active Low Output
Vm = Vss (delay multiplier = x1)
4000
3500
3000
2500
Ct = 100nF
2000
1500
1000
500
0
0
50
5V Active Low
Ct = 47nF
100
150
Timing Resistor Rt (K ohms)
Ct = 22nF
Ct = 10nF
200
250
4V Active Low
4000
3500
Ct = 47nF
3000
2500
Ct = 100nF
2000
1500
1000
500
0
0
50
100
150
Timing Resistor Rt (K ohms)
Ct = 22nF
Ct = 10nF
200
250
3500
3000
2500
Ct = 100nF
2000
1500
1000
500
0
0
50
3V Active Low
Ct = 47nF
Ct = 22nF
Ct = 10nF
100
150
200
250
Timing Resistor Rt (K ohms)
3500
3000
Ct = 100nF
2500
2000
1500
1000
500
0
0
50
2V Active Low
Ct = 47nF
Ct = 22nF
Ct = 10nF
100
150
200
250
Timing Resistor Rt (K ohms)
Example using a chart to calculate Rt and Ct
Requirements:
• Active low output (Vop connected to VSS)
• Auto-off delay 25 minutes
• VDD = 4V
1. Calculate Auto-off delay in seconds 25 x 60 = 1500.
2. Find ¹----⁵-₁--⁰----⁰- = 1500 on the 4V chart in Figure 3-10.
3. This shows the following suitable Ct / Rt combinations:
– 100 nF / 20 k
– 47 nF / 40 k
– 22 nF / 90 k
– 10 nF / 190 k
Note: the Auto-off delay times shown are nominal and will vary from chip to chip and with
capacitor and resistor tolerance.
16 AT42QT1012
9543D–AT42–08/10