3-1/2 DIGIT A/D CONVERTERS
TC14433
TC14433A
PIN DESCRIPTIONS
Pin No.
Pin No.
24-Pin
24-Pin
PDIP/CerDip SOIC
1
1
Pin No.
28-Pin
PLCC
2
Symbol
V
AG
Description
This is the analog ground; it has a high input impedance — This pin
determines the reference level for the unknown input voltage (V
X
) and the
reference voltage (V
REF
).
Reference voltage — Full-scale output is equal to the voltage applied to
V
REF
. Therefore, full-scale voltage of 1.999V requires 2V reference and
199.9 mV full-scale requires a 200 mV reference. V
REF
functions as system
reset also. When switched to V
EE
, the system is reset to the beginning of
the conversion cycle.
The unknown input voltage (V
X
) is measured as a ratio of the reference
voltage (V
REF
) in a ratiometric A/D conversion.
These pins are for external components used for the integration function in
the dual slope conversion. Typical values are 0.1
µF
(mylar) capacitor for C
1
.
R
1
= 470 kW (resistor) for 2V full-scale.
R
1
= 27 kW (resistor) for 200 mV full-scale. Clock frequency of 66 kHz gives
250 msec conversion time. See equation below for calculation of integrator
component values.
These pins are used for connecting the offset correction capacitor. The
recommended value is 0.1
µF.
Display update input pin — When DU is connected to the EOC output every
conversion is displayed. New data will be strobed into the output latches
during the conversion cycle if a positive edge is received on DU prior to the
ramp-down cycle. When this pin is driven from an external source, the
voltage should be referenced to V
SS
.
Clock input pins — The TC14433 has its own oscillator system clock.
Connecting a single resistor between CLK
1
and CLK
0
sets the clock frequency.
A crystal or OC circuit may be inserted in lieu of a resistor for improved
CLK
1
, the clock input, can be driven from an external clock source,
which need only have standard CMOS output drive. This pin is referenced to
V
EE
for external clock inputs. A 300 kW resistor yields a clock frequency of
about 66 kHz. (See typical characteristic curves; see Figure 9 for alternate
circuits.)
Negative power current — Connection pin for the most negative supply. Please
note the current for the output drive circuit is returned through V
SS
. Typical
supply current is 0.8 mA.
Negative power supply for output circuitry — This pin sets the low voltage level
for the output pins (BCD, Digit Selects, EOC, OR). When connected to analog
ground, the output voltage is from analog ground to V
DD
. If connected to V
EE
,
the output swing is from V
EE
to V
DD
. The recommended operating range for
V
SS
is between the V
DD
–3 volts and V
EE
.
End of conversion output generates a pulse at the end of each conversion
cycle. This generated pulse width is equal to one-half the period of the system
clock.
Overrange pin — Normally this pin is set high. When V
X
exceeds V
REF
the OR
pin is low.
2
2
3
V
REF
3
4
5
6
3
4
5
6
4
5
6
7
V
X
R
1
R
1
/C
1
C
1
7
8
9
7
8
9
9
10
11
CO
1
CO
2
DU
10
11
10
11
12
13
CLK
1
CLK
0
12
12
14
V
EE
13
13
16
V
SS
14
14
17
EOC
15
15
18
OR
3-130
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