QT102 Active Low output, VDD = 2V

0

500

1000

1500

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2500

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3500

4000

0

20406080

100

120

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160

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Tim ing Resistor Rt (K ohm s)

Ct=10nF

Ct=22nF

Ct=47nF

Ct=100nF

QT102 Active Low output, VDD = 3V

0

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3500

4000

0

20

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100

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Tim ing Resistor Rt (K ohm s)

Ct=10nF

Ct=22nF

Ct=47nF

Ct=100nF

QT102 Active Low output, VDD = 4V

0

500

1000

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2000

2500

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3500

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0

20

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Tim ing Resistor Rt (K ohm s)

Ct=10nF

Ct=22nF

Ct=47nF

Ct=100nF

QT102 Active Low output, VDD = 5V

0

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20

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60

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Tim ing Resistor Rt (K ohm s)

Ct=10nF

Ct=22nF

Ct=47nF

Ct=100nF

Figure 3.13 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 10 hours

• VDD = 4V

1. Calculate Auto-off delay in seconds 10 x 60 x 60 = 36000. This value is outside of the range of the charts so use the x24

multiplier (connect Rm to VDD).

Note: this will decrease the key sensitivity, so it may be necessary to increase the value of Cs.

2. Find 36000 = 1500 on the 4V chart in Figure 3.13

24

3. This shows the following Rt / Ct combinations: 100nF / 10k, 47nF / 27k, 22nF / 60k or 10nF / 130k

Note: the Auto-off delay times shown are nominal and will vary slightly from chip to chip and with capacitor and resistor

tolerance.

11

QT102_2R3.04_0807