MAX1246 Datasheet, PDF (17/24 Pages) Maxim Integrated Products – +2.7V, Low-Power, 4-Channel, Serial 12-Bit ADCs in QSOP-16

+2.7V, Low-Power, 4-Channel,
Serial 12-Bit ADCs in QSOP-16
Power-Down Sequencing
The MAX1246/MAX1247 auto power-down modes can
save considerable power when operating at less than
maximum sample rates. Figures 12, 13a, and 13b show
the average supply current as a function of the sam-
pling rate. The following discussion illustrates the vari-
ous power-down sequences.
Lowest Power at up to 500
Conversions/Channel/Second
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 13a depicts the MAX1246 power consumption
for one or four 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 14.
10,000
1000
AVERAGE SUPPLY CURRENT
vs. CONVERSION RATE
WITH EXTERNAL REFERENCE
VREF = V_DD = 3.0V
R_LOAD = ∞
CODE = 101010100000
100
4 CHANNELS
10
1 CHANNEL
1
0.1
0.1 1 10 100 1k 10k 100k 1M
CONVERSION RATE (Hz)
Figure 12. Average Supply Current vs. Conversion Rate with
External Reference
10,000
AVERAGE SUPPLY CURRENT
vs. CONVERSION RATE
(USING FASTPD)
R_LOAD = ∞
CODE = 101010100000
1000
4 CHANNELS
100
1 CHANNEL
AVERAGE SUPPLY CURRENT
vs. CONVERSION RATE
(USING FULLPD)
100
R_LOAD = ∞
CODE = 101010100000
4 CHANNELS
10
1 CHANNEL
1
0.01 0.1
1
10
100
1k
CONVERSION RATE (Hz)
Figure 13a. MAX1246 Supply Current vs. Conversion Rate,
FULLPD
TYPICAL REFERENCE-BUFFER POWER-UP
DELAY vs. TIME IN SHUTDOWN
2.0
1.5
1.0
10
0.5
1
0.1 1 10 100 1k 10k 100k 1M
CONVERSION RATE (Hz)
0.0
0.001
0.01
0.1
1
10
TIME IN SHUTDOWN (sec)
Figure 13b. MAX1246 Supply Current vs. Conversion Rate,
FASTPD
Figure 13c. Typical Reference-Buffer Power-Up Delay vs. Time
in Shutdown
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