3-179

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

capacitor. A polypropylene capacitor is suggested. Typical

values from 0.14

µF to 0.068 µF are satisfactory.

A 1

µF capacitor is suggested. Low leakage capacitors

such as polypropylene are recommended.

Several capacitor/resistor combinations for common

full-scale input conditions are given in Table 1.

Table 1 Suggested Component Values

2V

200 mV

20 mV

Full-Scale

Full-Scale

Full-Scale

REF

REF

2 M

Ω

200k

Ω

20k

Ω

0.033

µF

0.033

µF

0.033

µF

1

µF1µF1 F

0.068

µF

0.068

µF

0.14

µF

430k

Ω

430k

Ω

430k

Ω

NOTES: Approximately 5 conversions/second.

Differential Signal Inputs

The TC826 is designed with true differential inputs and

accepts input signals within the input stage common–mode

Common–mode voltages are removed from the system

when the TC826 operates from a battery or floating power

source (Isolated from measured system) and –IN is con-

In systems where common–mode rejection ratio mini-

mizes error. Common–mode voltages do, however, affect

the integrator output level. Integrator output saturation must

be prevented. A worse case condition exists if a large

differential signal. The negative signal drives the integrator

integrator output swing can be reduced below the recom-

mended 2V full–scale swing. The integrator output will swing

Digital Section

The TC826 contains all the segment drivers necessary

to drive a liquid crystal display (LCD). An LCD backplane

driver is included. The backplane frequency is the external

clock frequency divided by 256. A 430k

backplane frequency to approximately 55Hz with a 5V

nominal amplitude. When a segment driver is in phase with

the backplane signal the segment is ‘OFF’. An out–of–phase

segment drive signal causes the segment to be ‘ON’ or

visible. This AC drive configuration results in negligible DC

The internal voltage reference potential availabe at

analog-common will normally be used to supply the convert-

ers reference. This potential is stable whenever the supply

potential is greater than approximately 7V. In applications

where an externally generated reference voltage is desired

refer to Figure 6.

The reference voltage is adjusted with a near full-scale

input signal. Adjust for proper LCD display readout.

TC826

REF IN

ANALOG

COMMON

1.2V

REFERENCE

5

2

V

+

8

TC9491CZM

V

+

(b)

Figure 6. External Reference

Components Value Selection

The desired full-scale input voltage and output current

capability of the input buffer and integrator amplifier set the

integration resistor value. The internal class A output stage

amplifiers will supply a 1

µA drive durrent with minimal

current:

Where VFS = Full-Scale Analog Input

The integrating capacitor should be slected to maximize

intgrator output swing. The integrator output will swing to

The integrating capacitor is easily calculated:

Where :

The integrating capacitor should be selected for low

dielectric absorption to prevent roll-over errors. Polypro-

pylene capacitors are suggested.

VFS

VFS

640

)

TC826

A/D CONVERTER WITH

BAR GRAPH DISPLAY OUTPUT