LTC1196/LTC1198
O U
W
U
PPLICATI
A
S I FOR ATIO
Unipolar Output Code
Dummy Bits
INPUT VOLTAGE
(V = 5.000V)
The last 2 bits of the input word following the MUX
Address are dummy bits. Either bit can be a “logical
one” or a “logical zero.” These 2 bits allow the ADC 2.5
clocks to acquire the input signal after the channel
selection.
OUTPUT CODE
INPUT VOLTAGE
REF
4.9805V
1 1 1 1 1 1 1 1
V
V
– 1LSB
REF
REF
4.9609V
1 1 1 1 1 1 1 0
– 2LSB
•
•
•
•
•
•
•
•
•
0.0195V
0V
0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0
1LSB
0V
1196/98 AI05
A/D Conversion Result
Both the LTC1196 and the LTC1198 have the A/D
Operation with DIN and DOUT Tied Together
conversion result appear on the D
line after two null
OUT
The LTC1198 can be operated with DIN and DOUT tied
together. This eliminates one of the lines required to
communicate to the digitalsystems. Data is transmitted in
both directions on a single wire. The pin of the digital
systemsconnectedtothisdatalineshouldbeconfigurable
as either an input or an output. The LTC1198 will take
control of the data line and drive it low on the 5th falling
CLK edge after the start bit is received (see Figure 4).
Therefore the port line of the digital systems must be
switched to an input before this happens to avoid a
conflict.
bits (see Operating Sequence in Figures 1 and 2). Data
ontheD lineisupdatedontherisingedgeoftheCLK
OUT
line. The D
data should also be captured on the
OUT
risingCLKedgebythedigitalsystems.DataontheD
OUT
line remains valid for a minimum time of t
(30ns at
hDO
5V) to allow the capture to occur (see Figure 3).
V
IH
CLK
t
dDO
t
hDO
V
OH
D
OUT
V
OL
REDUCING POWER CONSUMPTION
1196/98 TC03
The LTC1196/LTC1198 can sample at up to a 1MHz rate,
drawing only 50mW from a 5V supply. Power consump-
tion can be reduced in two ways. Using a 3V supply lowers
thepowerconsumptiononbothdevicesbyafactoroffive,
to 10mW. The LTC1198 can reduce power even further
because it shuts down whenever it is not converting.
Figure 5 shows the supply current versus sample rate for
the LTC1196 and LTC1198 on 3V and 5V. To achieve such
a low power consumption, especially for the LTC1198,
several things must be taken into consideration.
Figure 3. Voltage Waveform for DOUT Delay Time,
tdDO and thDO
Unipolar Transfer Curve
The LTC1196/LTC1198 are permanently configured for
unipolar only. The input span and code assignment for
this conversion type are shown in the following figures.
Unipolar Transfer Curve
Shutdown (LTC1198)
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 0
Figure 2 shows the operating sequence of the LTC1198.
The converter draws power when the CS pin is low and
powersitselfdownwhenthatpinishigh. Forlowestpower
consumption in shutdown, the CS pin should be driven
with CMOS levels (0V to VCC) so that the CS input buffer
of the converter will not draw current.
•
•
•
0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0
V
IN
1196/98 AI04
16
Linear [ Linear ]
