Table 2b. Output Coding
COMP BINARY
.
BINARY
COMP TWO'S COMP
.
.
TWO'S COMP
.
INPUT
RANGE
BIPOLAR
±2.75V
SCALE
+2.749916
+FS –1 LSB
+2.749874 +FS –1 1/2 LSB
+2.062500
+3/4 FS
+1.375000
+1/2 FS
0.000000
0
–0.000084
–1 LSB
–1.375000
–1/2 FS
–2.062500
–3/4 FS
–2.749916
–FS +1 LSB
–2.749958 –FS + 1/2 LSB
–2.750000
–FS
INPUT
RANGE
UNIPOLAR
MSB
LSB MSB
LSB
0 to –5.5V
SCALE
0 –1 LSB
–0.000084 1111 1111 1111 1111 0000 0000 0000 0000
LSB "1" to "0"
LSB "0" to "1"
0 –1 1/2 LSB
–0.000126
0
0 – 1/8 FS
–0.687500 1110 0000 0000 0000 0001 1111 1111 1111
0
0 – 1/4 FS
–1.375000 1100 0000 0000 0000 0011 1111 1111 1111
0
–1/2 FS – 1/2LSB –2.749958 1000 0000 0000 0000 0111 1111 1111 1111
1
0
–1/2 LSB
–2.750000 0111 1111 1111 1111 1000 000 000 0000
0
–3/4 FS
–4.125000 0100 0000 0000 0000 1011 1111 1111 1111
0
–7/8 FS
–4.812500 0010 0000 0000 0000 1101 1111 1111 1111
1
0
–FS +1 LSB
–5.499916 0000 0000 0000 0001 1111 1111 1111 1110
LSB "0" to "1"
LSB "1" to "0"
–FS + 1/2 LSB
–5.499958
0
–FS
–5.500000 0000 0000 0000 0000 1111 1111 1111 1111
OFFSET BINARY
COMP OFF. BIN.
.
MSB
LSB
0111 1111 1111 1111
1
LSB "1" to "0"
0110 0000 0000 0000
0
0100 0000 0000 0000
0
0000 0000 0000 0000
0
1111 1111 1111 1111
1100 0000 0000 0000
0
1010 0000 0000 0000
0
1000 0000 0000 0001
1
LSB "0" to "1"
1000 0000 0000 0000
0
TWO'S COMP
.
MSB
LSB
1000 0000 0000 0000
LSB "0" to "1"
1001 1111 1111 1111
1011 1111 1111 1111
1111 1111 1111 1111
0000 0000 0000 0000
0011 1111 1111 1111
0101 1111 1111 1111
0111 1111 1111 1110
LSB "1" to "0"
0111 1111 1111 1111
COMP TWO'S COMP
.
.
THERMAL REQUIREMENTS
All DATEL sampling A/D converters are fully characterized
and specified over operating temperature (case) ranges of 0 to
+70°C and –55 to +125°C. All room-temperature (T
A
= +25°C)
production testing is performed without the use of heat sinks or
forced-air cooling. Thermal impedance figures for each device
are listed in their respective specification tables.
These devices do not normally require heat sinks, however,
standard precautionary design and layout procedures should
be used to ensure devices do not overheat. The ground and
power planes beneath the package, as well as all pcb signal
runs to and from the device, should be as heavy as possible
to help conduct heat away from the package. Electrically
insulating, thermally-conductive "pads" may be installed
N
N+1
underneath the package. Devices should be soldered to
boards rather than "socketed", and of course, minimal air
flow over the surface can greatly help reduce the package
temperature.
In more severe ambient conditions, the package/junction
temperature of a given device can be reduced dramatically
(typically 35%) by using one of DATEL's HS Series heat
sinks. See Ordering Information for the assigned part
number. See page 1-183 of the DATEL Data Acquisition
Components Catalog for more information on the HS Series.
Request DATEL Application Note AN-8, "Heat Sinks for DIP
Data Converters," or contact DATEL directly, for additional
information.
N+2
N+3
START
CONVERT
A q s
Acquisition Time
e
75ns typ.
5 s y
20ns typ.
0 s y
INTERNAL S/H
Hold
od
125ns typ.
p
50ns typ.
0 s y
2 n t p
20ns typ.
110ns typ.
p
Conversion Time
o v r o Tm
20ns typ.
0 s y .
1 0 s y
150ns typ.
Data N-2 Valid
Invalid
Data
Invalid
Data
Data N-1 Valid
EOC
OUTPUT
DATA
Data N-4 Valid
50ns typ.
Data N-3 Valid
NOTES:
1. Scale is approximately 20ns per didsion.fs = 5MHz
2. This device has three pipeline delays. Four start convert pulses (clock cycles) must be applied for valid data from the
first conversion to appear at the output of the A/D.
Figure 3. ADS-935 Timing Diagram
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