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TC9402 Scheda tecnica(PDF) 9 Page - Microchip Technology |
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TC9402 Scheda tecnica(HTML) 9 Page - Microchip Technology |
9 / 24 page © 2006 Microchip Technology Inc. DS21483C-page 9 TC9400/9401/9402 4.0 PIN FUNCTIONS 4.1 Threshold Detector Input In the V/F mode, this input is connected to the AMPLI- FIER OUT output (Pin 12) and triggers a 3 μsec pulse when the input voltage passes through its threshold. In the F/V mode, the input frequency is applied to this input. The nominal threshold of the detector is half way between the power supplies, or (VDD + VSS)/2 ±400 mV. The TC9400’s charge balancing V/F technique is not dependent on a precision comparator threshold, because the threshold only sets the lower limit of the op amp output. The op amp’s peak-to-peak output swing, which determines the frequency, is only influenced by external capacitors and by VREF. 4.2 Pulse Freq Out This output is an open drain N-channel FET, which provides a pulse waveform whose frequency is propor- tional to the input voltage. This output requires a pull- up resistor and interfaces directly with MOS, CMOS, and TTL logic (see Figure 4-1). 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. FIGURE 4-1: Output Waveforms 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 = 100 kΩ ±10%, unless otherwise noted. Increasing the maximum frequency of the TC9400 beyond 100 kHz 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 20 kΩ, which will typically produce a maximum full scale frequency of 500 kHz. 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. 3msec Typ. 1/f FOUT FOUT/2 Amp Out VREF 0V CREF CINT Notes: 1. To adjust FMIN, set VIN = 10 mV and adjust the 50 kW offset for 10 Hz output. 2. To adjust FMAX, set VIN = 10V and adjust RIN or VREF for 10 kHz output. 3. To increase FOUTMAX to 100 kHz, change CREF to 2pF and CINT to 75 pF. 4. For high performance applications, use high stability components for RIN, CREF, VREF (metal film resistors and glass capacitors). Also, separate output ground (Pin 9) from input ground (Pin 6). |
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