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QT113-IS Datasheet(PDF) 6 Page - ATMEL Corporation |
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QT113-IS Datasheet(HTML) 6 Page - ATMEL Corporation |
6 / 12 page Electromechanical devices like relays will usually ignore this short pulse. The pulse also has too low a duty cycle to visibly affect LED’s. It can be filtered completely if desired, by adding an RC timeconstant to filter the output, or if interfacing directly and only to a high-impedance CMOS input, by doing nothing or at most adding a small non-critical capacitor from Out to ground (Figure 2-5). The QT113H variant has an active-high output; the heartbeat signal of the QT113H works in exactly the same manner. 2.2.4 OUTPUT DRIVE The QT113’s `output is active low and can sink up to 5mA of non-inductive current. If an inductive load is used, such as a small relay, the load should be diode clamped to prevent damage. When set to operate in a proximity mode (at high gain) the current should be limited to 1mA to prevent gain shifting side effects from occurring, which happens 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 as described below. Care should be taken when the QT113 and the load are both powered from the same supply, and the supply is minimally regulated. The QT113 derives its internal references from the power supply, and sensitivity shifts can occur with changes in Vdd, as happens when loads are switched on. This can induce detection ‘cycling’, whereby an object is detected, the load is turned on, the supply sags, the detection is no longer sensed, the load is turned off, the supply rises and the object is reacquired, ad infinitum. To prevent this occurrence, the output should only be lightly loaded if the device is operated from an unregulated supply, e.g. batteries. Detection ‘stiction’, the opposite effect, can occur if a load is shed when Out is active. The output of the QT113 can directly drive a resistively limited LED. The LED should be connected with its cathode to the output and its anode towards Vcc, so that it lights when the sensor is active. If desired the LED can be connected from Out to ground, and driven on when the sensor is inactive. The QT113H variant has an active-high output. 3 - CIRCUIT GUIDELINES 3.1 SAMPLE CAPACITOR Charge sampler Cs can be virtually any plastic film or medium-K ceramic capacitor. The acceptable Cs range is from 10nF to 500nF depending on the sensitivity required; larger values of Cs demand higher stability to ensure reliable sensing. Acceptable capacitor types include polycarbonate, PPS film, or NPO/C0G ceramic. 3.2 OPTION STRAPPING The option pins Opt1 and Opt2 should never be left floating. If they are floated, the device will draw excess power and the options will not be properly read on powerup. Intentionally, there are no pullup resistors on these lines, since pullup resistors add to power drain if tied low. The Gain input should be connected to either Vdd or Gnd. Tables 1-1 and 2-1 show the option strap configurations available. 3.4 POWER SUPPLY, PCB LAYOUT The power supply can range from 2.5 to 5.0 volts. At 3 volts current drain averages less than 600µA in most cases, but can be higher if Cs is large. Increasing Cx values will actually decrease power drain. Operation can be from batteries, but be cautious about loads causing supply droop (see Output Drive, previous section). As battery voltage sags with use or fluctuates slowly with temperature, the QT113 will track and compensate for these changes automatically with only minor changes in sensitivity. If the power supply is shared with another electronic system, care should be taken to assure that the supply is free of - 6 - Figure 2-4 Using a micro to obtain HB pulses in either output state Figure 2-3 Getting HearBeat pulses with a pull-down resistor 3 46 5 1 +2 .5 to 5 7 2 OUT OPT 1 OPT 2 GAIN SNS1 SNS2 Vss Vd d 8 Ro H eartBeat™ P u lses Microcontroller PORT_M.x PORT_M.y 3 46 5 7 2 OUT OPT1 OPT2 GAIN SNS1 SNS2 Ro Figure 2-5 Eliminating HB Pulses 3 46 5 7 2 OUT OPT 1 OPT 2 GA IN SN S 1 SN S 2 CM O S 100p F Co G AT E OR MIC RO INPU T |
Similar Part No. - QT113-IS |
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Similar Description - QT113-IS |
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