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UC3702D датащи(PDF) 3 Page - Texas Instruments |
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UC3702D датащи(HTML) 3 Page - Texas Instruments |
3 / 6 page 3 UC1702 UC2702 UC3702 CT: A capacitor from the CT pin to ground sets the oscil- lator center frequency. Note that the oscillator period must be least an order of magnitude less than the relax- ation time constant (L/R) of the relay coil. However, a needlessly high operating frequency only increases power dissipation. For best accuracy, CT should be 220pF or greater. GND: Both ground pins must be connected to a low noise system ground. INA, INB, INC, IND: Separate digital control inputs for each of the four relay drivers. An active high input (a logic high) turns on the respective relay. Active low dis- ables the common-emitter drive transistor. OUTA, OUTB, OUTC, OUTD: Each of these output pins can be connected to the low side of one relay coil. The rated relay coil voltage of all relays to be driven by a sin- gle UC3702 must be the same. (It is permissible to use coils with different rated series resistances with a single UC3702, so long as the rated coil voltages are the same and care is taken with respect to the relaxation times of the different relay coils). Output transients are slew rate limited to decrease electro-magnetic radiation. R1: User selected external resistor must be placed from the R1 pin to the VBUS voltage supply. Sensing the VBUS amplitude, the oscillator varies its ON duty cycle such that the average voltage across the driver coil is constant. R2: User selected external resistor must placed from R2 pin to GND. This resistor, in conjunction with the external timing capacitor, CT, sets the OFF cycle time of the oscil- lator. For best accuracy, use 42.3k Ω for R2. RESET: Digital reset pin is active low. When RESET is low, the oscillator stops running and all drivers are open collector. VCC: Nominally 5V. In addition to supplying the voltage for the driver logic and oscillator circuit, the VCC supply is used as reference for the generating the average relay voltage. It is recommended that the VCC be regulated to ±5% of its nominal value or better to insure good regula- tion. Good decoupling with a minimum of 1 µF is neces- sary. VBUS: This pin should be tied to a low impedance volt- age source at some voltage higher than the rated voltage of the relay coil to be driven. VBUS may even be a poorly filtered rectified sin wave, as the UC3702 will reg- ulate the correct duty cycle. Good decoupling with a min- imum of 1 µF is necessary. PIN DESCRIPTIONS The UC3702 must be programmed for a specific relay voltage. The table given below has some suggested val- ues of R1, R2, and CT. The VCC supply voltage is as- sumed to be 5V. More generally, the following equation can be used to determine the equivalent average relay voltage: V VCC R R mV RELAY = •• • 106 1 22 400 . – Industrial Relays The UC3702 takes advantage of the inductance of the relay coil to regulate a constant coil current in a manner very similar to a switch-mode power supply. To use the UC3702 correctly, the coil characteristics must be known. The rated relay voltage is what the relay manu- facturers specify as voltage to drive the relay coil with if the coil were driven from a dc source. Most manufactur- ers also specify the series resistance of the coil. This is the resistance of the copper wire and determines the steady state coil ON current. For example, a 12V relay with a 320 series coil resistance with a draw of 37.5mA of constant current. The relay inductance is not typically specified in the manufacturer’s short-form datasheet, so the engineer will need an LCR bridge to measure it or re- quest the information from the relay manufacturer. APPLICATIONS INFORMATION Rated Relay Voltage R1 R2 CT 9V 153k Ω 43.2k Ω 220pF 12V 203k Ω 43.2k Ω 220pF 24V 398k Ω 43.2k Ω 220pF |
Аналогичный номер детали - UC3702D |
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Аналогичное описание - UC3702D |
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