MAX146ACAP Просмотр технического описания (PDF) - Maxim Integrated

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MAX146ACAP

+2.7V, Low-Power, 8-Channel, Serial 12-Bit ADCs

Maxim Integrated 

+2.7V, Low-Power, 8-Channel,

Serial 12-Bit ADCs

Power-Down Sequencing

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.

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.

10,000

1000

AVERAGE SUPPLY CURRENT

vs. CONVERSION RATE

WITH EXTERNAL REFERENCE

VREF = VDD = 3.0V

RLOAD = ∞

CODE = 101010100000

100

8 CHANNELS

10

1 CHANNEL

1

0.1

0.1 1 10 100 1k 10k 100k 1M

CONVERSION RATE (Hz)

Figure 13. Average Supply Current vs. Conversion Rate with

External Reference

10,000

AVERAGE SUPPLY CURRENT

vs. CONVERSION RATE

(USING FASTPD)

RLOAD = ∞

CODE = 101010100000

1000

8 CHANNELS

100

1 CHANNEL

10

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.

AVERAGE SUPPLY CURRENT

vs. CONVERSION RATE

(USING FULLPD)

100

RLOAD = ∞

CODE = 101010100000

10

8 CHANNELS

1 CHANNEL

1

0.01 0.1

1

10 100 1k

CONVERSION RATE (Hz)

Figure 14a. MAX146 Supply Current vs. Conversion Rate,

FULLPD

TYPICAL REFERENCE-BUFFER POWER-UP

DELAY vs. TIME IN SHUTDOWN

2.0

1.5

1.0

0.5

1

0.1 1 10 100 1k 10k 100k 1M

CONVERSION RATE (Hz)

Figure 14b. MAX146 Supply Current vs. Conversion Rate,

FASTPD

0

0.001

0.01

0.1

1

10

TIME IN SHUTDOWN (sec)

Figure 14c. Typical Reference-Buffer Power-Up Delay vs. Time

in Shutdown

18 ______________________________________________________________________________________

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