TC815 datasheet(21/26 Pages) MICROCHIP

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DS21474B-page 21

TC815

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

11.1

Display Decimal Point Selection

The TC815 provides a decimal point LCD drive signal.

The decimal point position is a function of the selected

full scale range, as shown in Table 11-1.

11.2

AC-to-DC Converter Operational

Amplifier

The TC815 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: 1 V/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. With external circuits, the

AC Operating mode can be used to perform other types

of functions within the constraints of the internal opera-

tional amplifier. External circuits that perform true RMS

conversion, or a peak hold function are typical

examples.

11.3

Component Selection

11.3.1

INTEGRATION RESISTOR

SELECTION

The TC815 automatically selects one of two external

integration resistors. RVBUF (pin 55) is selected for

voltage and current measurement. R

ΩBUF (Pin 54) is

selected for resistance measurements.

11.3.2

RVIBUF SELECTION (PIN 55)

In auto-range operation, the TC815 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:

VINT

Integrator swing = ±2V

Integration time = 100msec

Integration capacitor = 0.1µF

VMAX = Maximum input at VI = 300mV

EQUATION 11-1:

11.3.3

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 11-2):

VANCOM = Potential at Analog Common ≈ 2.7V

= 220

Ω

= 163.85

Ω

= 300

Ω

= Internal switch 33 resistance

≈ 600Ω

EQUATION 11-2:

TABLE 11-1:

DECIMAL POINT SELECTION

* 9

Full Scale Range

DP3

DP2

DP1

2000V, 2000k

Ω

OFF

200V, 200.0k

Ω

OFF

20V, 20.00k

Ω

OFF

2V, 2.000k

Ω

OFF

200V, 200.0

Ω

OFF

200mV, 200.0

Ω

OFF

20mA

OFF

200mA

OFF

RVIBUF =

VMAX(TI)

VINT(CI)

= 150k

Ω

ΩBUF =

VCC -(VANCOM)RX

(RX +RS +R1 +R8)

=0.63V

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