tc7109a Microchip Technology Inc., tc7109a Datasheet - Page 13

• Manufacturer Part Number: tc7109a
• Description: 12-bit ?-compatible Analog-to-digital Converters
• Manufacturer: Microchip Technology Inc.

FIGURE 3-5:
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 3-7:
© 2006 Microchip Technology Inc.
Integrator Output
High Byte Data
Low Byte Data
t = (2048 clock periods)
Internal Clock
Internal Latch
Status Output
Internal Mode
V+ or Open
Mode Input
Send Input
CE/LOAD
24
OSC
SEL
HBEN
LBEN
22
OSC
IN
UART
Norm
F
OSC
TC7109A RC Oscillator
TC7109A Handshake with Send Input Held Positive
= Don't Care
= 0.45/RC
Zero Crossing Occurs
23
OSC
OUT
3.58 MHz
R
Mode High Activates
CE/LOAD, HBEN, LBEN
58
C
Zero Crossing Detected
= 33.18 msec
25
Buffered
OSC OUT
Send Sensed
= Three-State
Data Valid
High-Impendance
FIGURE 3-6:
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.
Send Sensed
GND
Data Invalid
V+
24
OSC
SEL
= Three-State
will Pull-up
22
OSC
IN
Crystal
Crystal Oscillator
Terminates
UART Mode
23
OSC
OUT
TC7109/A
DS21456C-page 13
Mode Low, not
in Handshake Mode
Disables Outputs
CE/LOAD,
HBEN,
LBEN
25
Buffered
OSC OUT
Clock
÷
58