PDF OM1894 Data sheet ( Hoja de datos )

Número de pieza	OM1894
Descripción	Dual Sensing precision Triac Control IC
Fabricantes	IES
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No Preview Available ! Draft Data Sheet INTEGRATED CIRCUIT 2002 Nov 08 OM1894 Duwal wsewns.Dinag tparSechiseioent4trtUihaec.rcmcooomnsttraotl INTEGRATED ELECTRONIC SOLUTIONS 1BUTLER DRIVE HENDON SA 5014 AUSTRALIA www.DataSheet4U.com 1 page Integrated Electronic Solutions, Hendon, South Australia Dual sensing precision triac control thermostat Draft Data Sheet OM1894 6 FUNCTIONAL DESCRIPTION 6.1 VCC − Common, positive DC supply The positive DC supply rail for the control IC type OM1894 is used as the common reference. This is always connected to the T1 terminal of the triac, and being the positive supply rail allows negative gate drive to the triac in both positive and negative supply half cycles on T2. By driving the triac in this way the insensitive quadrant (negative T2 voltage, and positive gate triggering signal) of triacs is avoided. 6.2 VEE − Negative DC supply, substrate This pin connects to the substrate and the internally generated and regulated negative DC supply, and should be bypassed to VCC (common) by a capacitor of typically 100 µF. The capacitor needs to be sufficiently large to maintain the operating voltage during the half cycle when it is not being charged, as well as to provide the energy to drive the triac gate during the gate pulse. Internal supply sensing prevents the commencement of an ON cycle while the voltage is too low for reliable circuit operation. If during an ON cycle the supply voltage falls below this level the ON cycle will terminate at the first opportunity consistent with the logic cycle algorithm. 6.3 PWR − Power supply and synchronisation from the mains supply line The PWR input provides both a synchronisation signal for the logic functions of the OM1894, as well as the DC current used to provide the power supply from which the OM1894 is powered. Signals are derived which indicate the phase and magnitude of the signal on the AC supply. Three states, positive, zero and negative, of this signal is recognised for synchronisation of the triggering times to the mains. See Figure 3, OM1894 Power Supply Circuit. The PWR pin is driven by a current limiting resistor from the mains supply. During the positive half cycle current flows through the upper diode D1 to the positive common rail, while on a negative half cycle the current flows through the lower diode D2, and charges the VEE power supply capacitor. The zero crossing is signalled by the two comparators, the output signals of which indicate whether the mains voltage is above the common rail voltage, or below the negative VEE. There may be additional resistors in a simple network from the AC supply and VEE to adjust these zero-crossing signals to provide a symmetrical response in the positive as well as the negative going direction. As the AC signal passes through zero, comparators provide control signals Tp (when VPWR > VCC) and Tn (when VPWR < VEE) indicating whether the voltage on PWR pin is greater or less than VCC or VEE respectively. A resistor network ensures that these switching points correspond to equal positive or negative thresholds about the AC zero thus giving symmetrical zero-crossing information to the synchronisation and logic circuit. 2002 Nov 08 VCC D1 - Tp + PWR - D2 Tn + VEE psp1894 Fig.3 OM1894 power supply circuit 5 5 Page Integrated Electronic Solutions, Hendon, South Australia Dual sensing precision triac control thermostat Draft Data Sheet OM1894 SYMBOL PARAMETER Triac drive control input, pin CI Vthreshold Iin control input threshold input current Triac drive mode, pin MODE Vut upper mode threshold Vlt lower mode threshold Iin mode control input current CONDITIONS VCI = VCC Vmode = VCC or VEE MIN TYP MAX UNIT − −2 − V − − 1 µA − −0.6 − V − VEE+1.2 − V − − 10 µA 9 APPLICATION INFORMATION 9.1 Design considerations Resistors connected directly to the AC supply rail should be specified to withstand the voltage. It is recommended that (Philips BC Components) VR37 (or VR25) high-ohmic / high-voltage resistors be used. These resistors meet the safety requirements of a number of international standards on high voltage applications. 9.2 Sensor function For the two sensor sections of the OM1894, the function is as follows. When the current in SA is greater than the current in SB, then CAP is pulled low toward its lower (OFF) threshold. When it reaches this threshold and trips the latch, then the output pin pulls OP low towards VEE. When SB is greater than SA, and the voltage on CAP reaches the upper threshold, then the output is switched HIGH pulling OP high towards VCC with a significantly larger current than when pulled low. If OP1 and OP2 are connected together, then if either OP1 or OP2 is pulled into the HIGH state, then the combined output is pulled HIGH. To give a low output both OP1 AND OP2 must be LOW. OP1 and OP2 will directly drive standard 4000 series CMOS logic gates (for example Philips HEF4xxx). Pull-down resistors are not needed. They may also be used to drive inputs on a microcontroller. 9.3 Triac drive control input, and mode The control input (CI) is a high impedance voltage sensing input and may be driven by either one (or both connected together) of the OP1 and OP2 sensing circuit outputs. It can also be driven by a standard CMOS gate output, or microcontroller output. If used with a microcontroller the input threshold voltage has been chosen to be suitable for use with a micro running off its own power supply with VCC connected to VDD on the micro. This input is active HIGH if the MODE pin is connected to VCC. If MODE is connected to VEE, the input sense of CI is inverted, and it is active LOW: that is gate pulse are applied to turn the triac ON, when the signal on CI is LOW. When MODE is not connected, then internal logic takes the signals of OP1 and OP2 and combines them so that starting from an initial OFF state, the triac will only be turned ON when both of the input sensing circuits have their ON latch set (that is when both OP1 and OP2 are high). The run cycle is latched, end even when OP1 and OP2 might go LOW individually, the run cycle is not stopped until both OP1 and OP2 are low, and both input sensor circuit latches have been set to the OFF state. 9.4 Gate drive The 300 Ω gate resistor shown in the application circuits gives a little over 10 mA gate drive. Thus for the circuit shown a triac would need to be specified that is suitable for 10 mA triggering with negative triggering signal for both positive and negative voltage on T2. From the threshold levels determined from the resistive network on PWR, and the AC supply, the timing of the first gate pulse in a conduction cycle can be calculated (assuming a sine wave supply). The specification of the triac will indicate the latching current for switch-on, and knowing the minimum load with which the circuit is to operate, then proper design will ensure that the gate pulse will be long enough, and will not be removed before the triac current reaches this figure. 9.5 Pulse width extension When the gate pulse is extended by adding a parallel resistor and capacitor from the pulse width extension pin PX to VEE, the power supply current used in driving the gate is a major portion of the available DC 2002 Nov 08 11 11 Page

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