14
LTC1594L/LTC1598L
15948lfb
APPLICATIONS INFORMATION
WUU
U
CLK
EN D1
D2
CSMUX
CSADC
B5
B6
B7
B8B9
B10B11
D
OUT
CH0 TO
CH7
D
IN
t
CONV
t
suCS
NULL
BIT
D0
B4
B3
B2 B1 B0
EN D1
t
SMPL
t
ON
t
ON
B5
B6
B7
B8B9
B10B11
t
CONV
t
suCS
NULL
BIT
D0D2
EN D1
D0D2
B4
B3
B2 B1 B0
t
SMPL
ADCIN =
MUXOUT
COM = GND
1594L/98L F05
B4
B3
B2 B1 B0
DON’T CARE DON’T CARE
MUXOUT/ADCIN Loop Economizes
Signal Conditioning
The MUXOUT and ADCIN pins of the LTC1594L/LTC1598L
form a very flexible external loop that allows Program-
mable Gain Amplifier (PGA) and/or processing analog
input signals prior to conversion. This loop is also a cost
effective way to perform the conditioning, because only
one circuit is needed instead of one for each channel.
In the Typical Applications section, there are a few
examples illustrating how to use the MUXOUT/ADCIN loop
to form a PGA and to antialias filter several analog inputs.
ACHIEVING MICROPOWER PERFORMANCE
With typical operating currents of 160µA and automatic
shutdown between conversions, the LTC1594L/
LTC1598L achieve extremely low power consumption
over a wide range of sample rates (see Figure 6). The auto
shutdown allows the supply current to drop with reduced
sample rate. Several things must be taken into account to
achieve such a low power consumption.
Shutdown
The LTC1594L/LTC1598L are equipped with automatic
shutdown features. They draw power when the CS pin is
low. The bias circuits and comparator of the ADC powers
down and the reference input becomes high impedance at
the end of each conversion leaving the CLK running to
clock out the LSB first data or zeroes (see Figures 1 and 2).
When the CS pin is high, the ADC powers down completely
leaving the CLK running to clock the input data word into
MUX. If the CS, D
IN
and CLK are not running rail-to-rail, the
input logic buffers will draw currents. These currents may
be large compared to the typical supply current. To obtain
the lowest supply current, run the CS, D
IN
and CLK pins
rail-to-rail.
D
OUT
Loading
Capacitive loading on the digital output can increase
power consumption. A 100pF capacitor on the D
OUT
pin
can add more than 50µA to the supply current at a 200kHz
clock frequency. An extra 50µA or so of current goes into
charging and discharging the load capacitor. The same
goes for digital lines driven at a high frequency by any
logic. The (C)(V)(f) currents must be evaluated and the
troublesome ones minimized.
Figure 5. Use Separate Chip Selects to Maximize Sample Rate
Figure 6. Automatic Power Shutdown Between Conversions
Allows Power Consumption to Drop with Sample Rate
SAMPLE FREQUENCY (kHz)
0.1
1
SUPPLY CURRENT (µA)
10
100
1000
1 10 100
1594L/98L G01
T
A
= 25°C
V
CC
= 2.7V
V
REF
= 2.5V
f
CLK
= 200kHz
