TC818A datasheet(19/24 Pages) MICROCHIP

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DS21475B-page 19

TC818A

Vendors for piezo electric audio transducers are:

• Gulton Industries

Piezo Products Division

212 Durham Avenue

Metuchen, New Jersey 08840

(201) 548-2800

Typical P/Ns: 102-95NS, 101-FB-00

• Taiyo Yuden (USA) Inc.

Arlington Center

714 West Algonquin Road

Arlington Heights, Illinois 60005

Typical P/Ns: CB27BB, CB20BB, CB355BB

3.18

Display Decimal Point Selection

The TC818A provides a decimal point LCD drive sig-

nal. The decimal point position is a function of the

selected full scale range, as shown in Table 3-5.

3.19

AC-to-DC Converter Operational

Amplifier

The TC818A contains an on-chip operational amplifier

that may be connected as a rectifier for AC-to-DC volt-

age and current measurements. Typical operational

amplifier characteristics are:

• Slew Rate: 1V/

µsec

• Unity Gain Bandwidth: 0.4MHz

• Open Loop Gain: 44dB

• Output Voltage Swing (Load = 10k

Ω) ± 1.5V

(Referenced to Analog Common)

When the AC measurement option is selected, the

input buffer receives an input signal through switch

S14, rather than switch S11 (see Figure 3-1). With

external circuits, the AC Operating mode can be used

to perform other types of functions within the con-

straints of the internal operational amplifier. External

circuits that perform true RMS conversion, or a peak

hold function, are typical examples.

3.20

Component Selection

3.20.1

INTEGRATION RESISTOR

SELECTION

The TC818A automatically selects one of two external

integration resistors. RVIBUF (Pin 55) is selected for

voltage and current measurement. R

ΩBUF (Pin 54) is

selected for resistance measurements.

3.20.2

RVIBUF SELECTION (PIN 55)

In auto-range operation, the TC818A operates with a

200mV maximum full scale potential at VI (Pin 44).

Resistive dividers at VR2 (Pin 41), VR3 (Pin 40), VR4

(Pin 43), and VR5 (Pin 42) are automatically switched

to maintain the 200V full scale potential.

In Manual mode, the Extended Operating mode is acti-

vated, giving a 300mV full scale potential at VI (Pin 44).

The integrator output swing should be maximized, but

saturations must be avoided. The integrator will swing

within 0.45V of VCC (Pin 28) and 0.5V of VSS (Pin 57)

without saturating. A ±2V swing is suggested. The

value of RVIBUF is easily calculated, assuming a worst

case extended resolution input signal:

Where:

VINT = Integrator swing = ±2V

= Integration time = 100msec

= Integration capacitor = 0.1

µF

VMAX = Maximum input at VI = 300mV

EQUATION 3-1:

3.20.3

ΩBUF SELECTION (PIN 54)

In ratiometric resistance measurements, the signal at

RX (Pin 50) is always positive, with respect to analog

common. The integrator swings negative.

The worst case integrator swing is for the 200

Ω range

with the manual, extended resolution option.

The input voltage, VX (Pin 50) is easily calculated (see

Figure 3-15).

TABLE 3-5:

DECIMAL POINT SELECTION

Full Scale Range

1* 9

* 9

DP3

DP2

DP1

2000V, 2000k

Ω

OFF

200V, 200k

Ω

OFF

20V, 20k

Ω

OFF

2V, 2k

Ω

OFF

200V, 200

Ω

OFF

200mV, 200

Ω

OFF

20mA

OFF

200mA

OFF

RVIBUF =

VMAX(TI)

VINT(CI)

= 150k

Ω

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