3-161

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

TC820

3-3/4 A/D CONVERTER WITH

FREQUENCY COUNTER

AND LOGIC PROBE

To prevent roll-over-type errors from being induced by

pared to stray node capacitance. A 0.1

µF capacitor is

typical.

The TC820 offers a significantly improved analog

common temperature coefficient, providing a very stable

voltage suitable for use as a voltage reference. The

temperature coefficient of analog common is typically

35ppm/

°C.

Figure 7. LCD During Logic Probe Operation

HIGH

LOW

*

**

"HIGH" ANNUNCIATOR WILL BE ON WHEN DP1/HI =

LOGIC HIGH

"LOW" ANNUNCIATOR AND BUZZER WILL BE ON

WHEN DP0/LO = LOGIC HIGH

**

*

Analog Common

The analog common pin is set at a voltage potential

is tied internally to an N-channel FET capable of sinking

should an external load attempt to pull the common line

12

µA, and is therefore easily pulled to a more negative

The TC820 connects the internal V

+

–

analog common during the auto-zero cycle. During the

reference integrate phase, V

–

common. If V

–

a common-mode voltage exists. This is rejected by the

converter's 86dB common-mode rejection ratio. In battery-

powered applications, analog common and V

–

connected, removing common-mode voltage concerns. In

systems where V

–

or to a given voltage, analog common should be connected

to V

–

The analog common pin serves to set the analog section

reference or common point. The TC820 is specifically

designed to operate from a battery or in any measurement

TC820

GND

GND

V

+

V

–

V

+

V

–

MEASURED

SYSTEM

POWER

SOURCE

9V

V

+

REF

V

–

REF

+

–

BP1

INT

V

BP3

BP2

OSC1

OSC2

OSC3 NC

SEGMENT

DRIVE

LCD

ANALOG

COMMON

+

Figure 8. Common-Mode Voltage Removed in Battery Operation With V

–