TC9400 Просмотр технического описания (PDF) - Microchip Technology

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TC9400

Voltage-to-Frequency/Frequency-to-Voltage Converters

Microchip Technology 

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 3µsec). 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.

TC9400/9401/9402

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 10µA is specified, but an over range

current up to 50µA 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 0.1µF bypass

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 x CREF, is removed

from the integrator capacitor. After about 3µsec, this pin

is internally connected to the summing junction of the

Op Amp to discharge CREF. Break-before-make switch-

ing ensures that the reference voltage is not directly

applied to the summing junction.

© 2002 Microchip Technology Inc.

DS21483B-page 9

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