TC7109 datasheet(13/30 Pages) MICROCHIP

13 / 30 page

DS21456C-page 13

TC7109/A

FIGURE 3-5:

TC7109A RC Oscillator

With OSCILLATOR SELECT input LOW, two on-chip

capacitors and a feedback device are added to the

oscillator. In this configuration, the oscillator will oper-

ate with most crystals in the 1MHz to 5MHz range, with

no external components (Figure ). The OSCILLATOR

SELECT input LOW inserts a fixed 458 divider circuit

between the BUFFERED OSCILLATOR OUTPUT and

the internal clock. A 3.58MHz TV crystal gives a

division ratio, providing an integration time given by:

EQUATION 3-1:

FIGURE 3-6:

Crystal Oscillator

The error is less than 1% from two 60Hz periods, or

33.33msec, which will give better than 40dB, 60Hz

rejection. The converter will operate reliably at conver-

sion rates up to 30 per second, corresponding to a

clock frequency of 245.8kHz.

When the oscillator is to be over driven, the OSCILLA-

TOR OUTPUT should be left open, and the over driving

signal should be applied at the OSCILLATOR INPUT.

The internal clock will be of the same duty cycle, fre-

quency and phase as the input signal. When the

OSCILLATOR SELECT is at GND, the clock will be

1/58 of the input frequency.

FIGURE 3-7:

TC7109A Handshake with Send Input Held Positive

OSC

OUT

Buffered

OSC OUT

OSC

SEL

V+ or Open

OSC

FOSC = 0.45/RC

t = (2048 clock periods)

= 33.18 msec

3.58 MHz

OSC

OUT

Buffered

OSC OUT

OSC

SEL

GND

V+

OSC

Clock

Crystal

= Three-State

High-Impendance

Integrator Output

Data Invalid

Data Valid

Internal Clock

Internal Latch

Status Output

Mode Input

Internal Mode

Send Input

CE/LOAD

HBEN

High Byte Data

LBEN

Low Byte Data

= Don't Care

= Three-State

will Pull-up

UART

Norm

Terminates

UART Mode

Zero Crossing Detected

Zero Crossing Occurs

Send Sensed

Mode Low, not

in Handshake Mode

Disables Outputs

CE/LOAD,

HBEN,

LBEN

Mode High Activates

CE/LOAD, HBEN, LBEN

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