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TC9400CPD Datasheet(PDF) 9 Page - Microchip Technology |
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TC9400CPD Datasheet(HTML) 9 Page - Microchip Technology |
9 / 20 page ![]() © 2002 Microchip Technology Inc. DS21483B-page 9 TC9400/9401/9402 4.3 Freq/2 Out This output is an open drain N-channel FET, which pro- vides a square wave one-half the frequency of the pulse frequency output. The FREQ/2 OUT output will change state on the rising edge of PULSE FREQ OUT. This output requires a pull-up resistor and interfaces directly with MOS, CMOS, and TTL logic. 4.4 Output Common The sources of both the FREQ/2 OUT and the PULSE FREQ OUT are connected to this pin. An output level swing from the drain voltage to ground, or to the VSS supply, may be obtained by connecting this pin to the appropriate point. 4.5 RBIAS An external resistor, connected to VSS, sets the bias point for the TC9400. Specifications for the TC9400 are based on RBIAS = 100kΩ ±10%, unless otherwise noted. Increasing the maximum frequency of the TC9400 beyond 100kHz is limited by the pulse width of the pulse output (typically 3 µsec). Reducing RBIAS will decrease the pulse width and increase the maximum operating frequency, but linearity errors will also increase. RBIAS can be reduced to 20kΩ,which will typically produce a maximum full scale frequency of 500kHz. 4.6 Amplifier Out This pin is the output stage of the operational amplifier. During V/F operation, a negative going ramp signal is available at this pin. In the F/V mode, a voltage proportional to the frequency input is generated. 4.7 Zero Adjust This pin is the non-inverting input of the operational amplifier. The low frequency set point is determined by adjusting the voltage at this pin. 4.8 IIN The inverting input of the operational amplifier and the summing junction when connected in the V/F mode. An input current of 10 µA is specified, but an over range current up to 50 µA can be used without detrimental effect to the circuit operation. IIN connects the summing junction of an operational amplifier. Voltage sources cannot be attached directly, but must be buffered by external resistors. 4.9 VREF A reference voltage from either a precision source, or the VSS supply is applied to this pin. Accuracy of the TC9400 is dependent on the voltage regulation and temperature characteristics of the reference circuitry. Since the TC9400 is a charge balancing V/F converter, the reference current will be equal to the input current. For this reason, the DC impedance of the reference voltage source must be kept low enough to prevent lin- earity errors. For linearity of 0.01%, a reference imped- ance of 200W or less is recommended. A 0.1 µFbypass capacitor should be connected from VREF to ground. 4.10 VREF Out The charging current for CREF is supplied through this pin. When the Op Amp output reaches the threshold level, this pin is internally connected to the reference voltage and a charge, equal to VREF xCREF, is removed from the integrator capacitor. After about 3 µsec, this pin is internally connected to the summing junction of the Op Amptodischarge CREF. Break-before-make switch- ing ensures that the reference voltage is not directly applied to the summing junction. |
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