Datasheet

LTC1096/LTC1096L
LTC1098/LTC1098L
19
10968fc
APPLICATIONS INFORMATION
Figure 3. LTC1098(L) Operation with D
IN
and D
OUT
Tied Together
Figure 4. Automatic Power Shutdown Between Conversions
Allows Power Consumption to Drop with Sample Rate
Figure 5. After a Conversion, When the Microprocessor
Drives CS High, the ADC Automatically Shuts Down Until the
Next Conversion. The Supply Current, Which Is Very Low
During cConversions, Drops to Zero in Shutdown
the data line and drive it low on the 4th falling CLK edge
after the start bit is received (see Figure 3). Therefore the
processor port line must be switched to an input before
this happens, to avoid a confl ict.
In the Typical Applications section, there is an example of
interfacing the LTC1098(L) with D
IN
and D
OUT
tied together
to the Intel 8051 MPU.
ACHIEVING MICROPOWER PERFORMANCE
With typical operating currents of 40μA and automatic
shutdown between conversions, the LTC1096/LTC1098
achieves extremely low power consumption over a wide
range of sample rates (see Figure 4). In systems that
convert continuously, the LTC1096/LTC1098 will draw
1
2 3 4
CS
CLK
DATA (D
IN
/D
OUT
) START SGL/DIFF ODD/SIGN MSBF B7 B6
•••
MSBF BIT LATCHED
BY LTC1098(L)
LTC1098(L) CONTROLS DATA LINE AND SENDS
A/D RESULT BACK TO MPU
MPU CONTROLS DATA LINE AND SENDS
MUX ADDRESS TO LTC1098(L)
PROCESSOR MUST RELEASE
DATA LINE AFTER 4TH RISING CLK
AND BEFORE THE 4TH FALLING CLK
LTC1098(L) TAKES CONTROL OF
DATA LINE ON 4TH FALLING CLK
10968 F03
its normal operating power continuously. Figure 5 shows
that the typical current varies from 40μA at clock rates
below 50kHz to 100μA at 500kHz. Several things must
be taken into account to achieve such a low power
consumption.
Sample Rate, f
SAMPLE
(kHz)
0.1
1
SUPPLY CURRENT, I
CC
(μA)
10
100
1000
1 10 100
10968 F04
T
A
= 25°C
V
CC
= 5V
CLOCK FREQUENCY (Hz)
20
SUPPLY CURRENT, I
CC
(μA)
60
80
120
140
100 10k 100k 1M
10968 F05
0
1k
100
40
0.002
T
A
= 25°C
V
CC
= 5V
ACTIVE (CS LOW)
SHUTDOWN (CS HIGH)
SUPPLY CURRENT vs CLOCK RATE FOR
ACTIVE AND SHUTDOWN MODES
Shutdown
Figures 1 and 2 show the operating sequence of the
LTC1096/LTC1098. The converter draws power when the
CS pin is low and powers itself down when that pin is high.
If the CS pin is not taken to ground when it is low and not
taken to supply voltage when it is high, the input buffers