at42qt100a ATMEL Corporation, at42qt100a Datasheet - Page 10

• Manufacturer Part Number: at42qt100a
• Description: Qtouch? Charge Transfer Ic
• Manufacturer: ATMEL Corporation

3.9.3
10
AT42QT100A
Output Drive
Figure 3-6.
If the sensor is wired to a microcontroller as shown in
reconfigure the load resistor to either Vss or Vdd depending on the output state of the QT100A,
so that the pulses are evident in either state.
Figure 3-7.
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.
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.
Obtaining HeartBeat Pulses with a Pull-up Resistor (6-pin WSON Package)
Using a Microcontroller to Obtain HeartBeat Pulses in Either Output State (6-pin
WSON Package)
Microcontroller
HeartBeat™ Pulses
Port_M.x
Port_M.y
Ro
1
OUT
R0
VDD
VSS
VDD
2
5
SNSK
SYNC
SNS
1
OUT
3
4
6
SYNC
SNSK
SNS
Figure
3
4
6
3-7, the microcontroller can
9531A–AT42–02/09