MAX146 Maxim, MAX146 Datasheet - Page 18

• Manufacturer Part Number: MAX146
• Description: +2.7Low-Power / 8-Channel / Serial 12-Bit ADCs
• Manufacturer: Maxim

+2.7V, Low-Power, 8-Channel,
Serial 12-Bit ADCs
The MAX146/MAX147 auto power-down modes can
save considerable power when operating at less than
maximum sample rates. Figures 13, 14a, and 14b show
the average supply current as a function of the sam-
pling rate. The following discussion illustrates the vari-
ous power-down sequences.
The following examples show two different power-down
sequences. Other combinations of clock rates, compen-
sation modes, and power-down modes may give lowest
power consumption in other applications.
Figure 13. Average Supply Current vs. Conversion Rate with
External Reference
Figure 14b. MAX146 Supply Current vs. Conversion Rate,
FASTPD
18
______________________________________________________________________________________
10,000
10,000
1000
1000
100
100
0.1
10
10
1
1
0.1
0.1
V REF = V
R
CODE = 101010100000
R
CODE = 101010100000
LOAD
LOAD
WITH EXTERNAL REFERENCE
1
AVERAGE SUPPLY CURRENT
AVERAGE SUPPLY CURRENT
1
=
=
vs. CONVERSION RATE
vs. CONVERSION RATE
DD
8 CHANNELS
10
CONVERSION RATE (Hz)
CONVERSION RATE (Hz)
10
Power-Down Sequencing
= 3.0V
8 CHANNELS
Conversions/Channel/Second
(USING FASTPD)
100
100
Lowest Power at up to 500
1k
1k
1 CHANNEL
1 CHANNEL
10k
10k
100k
100k
1M
1M
Figure 14a depicts the MAX146 power consumption for
one or eight channel conversions utilizing full power-
down mode and internal-reference compensation. A
0.047µF bypass capacitor at REFADJ forms an RC filter
with the internal 20kΩ reference resistor with a 0.9ms
time constant. To achieve full 12-bit accuracy, 10 time
constants or 9ms are required after power-up. Waiting
this 9ms in FASTPD mode instead of in full power-up
can reduce power consumption by a factor of 10 or
more. This is achieved by using the sequence shown in
Figure 15.
Figure 14a. MAX146 Supply Current vs. Conversion Rate,
FULLPD
Figure 14c. Typical Reference-Buffer Power-Up Delay vs. Time
in Shutdown
100
2.0
1.5
1.0
0.5
10
1
0
0.001
TYPICAL REFERENCE-BUFFER POWER-UP
0.01
R
CODE = 101010100000
LOAD
DELAY vs. TIME IN SHUTDOWN
AVERAGE SUPPLY CURRENT
0.1
=
vs. CONVERSION RATE
0.01
TIME IN SHUTDOWN (sec)
CONVERSION RATE (Hz)
(USING FULLPD)
8 CHANNELS
1
0.1
10
1 CHANNEL
1
100
1k
10