Figure 1 - Analog Input Full-Scale Range
V
REF
+
+FS
MODES OF OPERATION
The SPT7830 has three modes of operation.The mode of
operation is based strictly on how the
SC
is used.
Full-Scale Range
6% of [(V
REF
+) - (V
REF
-)]
SINGLE SHOT MODE
When
SC
goes low, conversion starts on the next rising edge
of the clock (defined as the first conversion clock). The MSB
of data is valid 8 ns after the falling edge of the fourth
conversion clock. (See figure 8, Data Output Timing.)
The conversion is complete after 14 clock cycles. At the
falling edge of the fourteenth clock cycle, if
SC
is high (not
selected), the data output goes to a high impedance state,
and no more conversions will take place until the next
SC
low
event. (See the single shot mode timing diagram in figure 4.)
SYNCHRONIZED MODE
4% of [(V
REF
+) - (V
REF
-)]
-FS
V
REF
-
The drive requirements for the analog input are minimal
when compared to most other converters due to the
SPT7830’s extremely low input capacitance of only 5 pF and
very high input resistance of greater than 5 MΩ.
If the input buffer amplifier supply voltages are greater than
V
DD
+ 0.7 V or less than Ground - 0.7 V, the analog input
should be protected through a series resistor and a diode
clamping circuit as shown in figure 2.
Figure 2 - Recommended Input Protection Circuit
+V
AV
DD
When
SC
goes low, conversion will start on the next rising
edge of the clock (defined as the first conversion clock). The
MSB is valid 8 ns after the falling edge of the fourth conver-
sion clock.
The first conversion is complete after 14 clock cycles. At any
time after the falling edge of the fourteenth clock cycle,
SC
may go low again to initiate the next conversion. When the
SC
goes low, the conversion starts on the rising edge of the
next clock. (See the synchronized mode timing diagram in
figure 5.)
The data output will go to a high impedance state until the
next conversion is initiated.
FREE RUN MODE
When
SC
goes low, conversion starts on the next rising edge
of the clock (defined as the first conversion clock). The MSB
data is valid 8 ns after the falling edge of the fourth conver-
sion clock.
As long as
SC
is held low, the device operates in the free run
mode. New conversions start after every fourteenth cycle
with valid data available 8 ns after the falling edge of the
fourth clock within each new conversion cycle.
The data output remains low between conversion cycles.
(See the free run mode timing diagram in figure 6.)
D1
Buffer
47
Ω
D2
ADC
-V
D1 = D2 = Hewlett Packard HP5712 or equivalent
INPUT PROTECTION
All I/O pads are protected with an on-chip protection circuit
shown in figure 3. This circuit provides ESD robustness to
>3.0 kV and prevents latch-up under severe discharge
conditions without degrading analog transition times.
Figure 3 - On-Chip Protection Circuit
V
DD
120
Ω
Analog
120
Ω
Pad
SPT7830
5
12/29/99
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
