ADS7819 Datasheet, PDF (7/11 Pages) Burr-Brown (TI) – 12-Bit 800kHz Sampling CMOS ANALOG-to-DIGITAL CONVERTER

BASIC OPERATION
Figure 1 shows a basic circuit to operate the ADS7819.
Taking R/C (pin 23) LOW for 40ns will initiate a conver-
sion. BUSY (pin 25) will go LOW and stay LOW until the
conversion is completed and the output registers are up-
dated. Data will be output in Binary Two’s Complement
with the MSB on D11 (pin 6). BUSY going HIGH can be
used to latch the data. All convert commands will be ignored
while BUSY is LOW.
CS R/C BUSY OPERATION
1
X
X None. Databus in Hi-Z state.
↓
0
1
Initiates conversion. Databus remains in
Hi-Z state.
0
↓
1
Initiates conversion. Databus enters Hi-Z
state.
0
1
↑
Conversion completed. Valid data from the
most recent conversion on the databus.
↓
1
1
Enables databus with valid data from the
most recent conversion.
↓
1
0
Conversion in progress. Databus in Hi-Z
state, enabled when the conversion is completed.
0
↑
0
Conversion in progress. Databus in Hi-Z
state, enabled when the conversion is completed.
0
0
↑
Conversion completed. Valid data from the
most recent conversion in the output register
but the output pins D11-D0 are tri-stated.
X
X
0
New convert commands ignored. Conversion
in progress.
Table I. Control Line Functions for ‘read’ and ‘convert’.
The ADS7819 will begin tracking the input signal at the end
of the conversion. Allowing 1.25µs between convert com-
mands assures accurate acquisition of a new signal.
STARTING A CONVERSION
The combination of CS (pin 24) and R/C (pin 23) LOW for
a minimum of 40ns puts the sample/hold of the ADS7819 in
the hold state and starts a conversion. BUSY (pin 25) will go
LOW and stay LOW until the conversion is completed and
the internal output register has been updated. All new
convert commands during BUSY LOW will be ignored.
2 The ADS7819 will begin tracking the input signal at the end
of the conversion. Allowing 1.25µs between convert com-
mands assures accurate acquisition of a new signal. Refer to
Table I for a summary of CS, R/C, and BUSY states and
Figures 2 and 3 for timing parameters.
DESCRIPTION ANALOG VALUE
DIGITAL OUTPUT
Full Scale Range
Least Significant
Bit (LSB)
±2.5V
1.22mV
BINARY TWO'S COMPLEMENT
BINARY CODE HEX CODE
+Full Scale
(2.5V – 1LSB)
2.499V
0111 1111 1111
7FF
Midscale
0V
0000 0000 0000
000
One LSB below
–1.22mV
1111 1111 1111
FFF
Midscale
–Full Scale
–2.5V
1000 0000 0000
800
TABLE II. Ideal Input Voltages and Output Codes.
±2.5V
D11 (MSB)
D10
D9
D8
D7
D6
D5
D4
50Ω
0.1µF
1
2
3
10µF
+4
5
6
7
8
9
10
11
12
13
14
ADS7819
28
27
26
25
24
23
22
21
20
19 _NC
18
17
16
15
0.1µF 10µF
+
+5V
0.1µF 10µF
–5V
+
BUSY
Convert Pulse
40ns min
D0 (LSB)
D1
D2
D3
FIGURE 1. Basic Operation
®
7
ADS7819