© 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

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

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

supply, may be obtained by connecting this pin to the

appropriate point.

4.5

point for the TC9400. Specifications for the TC9400 are

noted.

Increasing the maximum frequency of the TC9400

beyond 100 kHz is limited by the pulse width of the

pulse output (typically 3

decrease the pulse width and increase the maximum

operating frequency, but linearity errors will also

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

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

junction of an operational amplifier. Voltage sources

cannot be attached directly, but must be buffered by

external resistors.

3msec

Typ.

1/f

Amp Out

0V

Notes:

resistors and glass capacitors). Also, separate output ground (Pin 9) from input ground (Pin 6).