MAX188 データシートの表示（PDF） - Maxim Integrated

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MAX188

Low-Power, 8-Channel, Serial 12-Bit ADCs

Maxim Integrated 

Low-Power, 8-Channel,

Serial 12-Bit ADCs

MAX186

FULL POWER-DOWN

1000

2ms FASTPD WAIT

400kHz EXTERNAL CLOCK

INTERNAL COMPENSATION

8 CHANNELS

100

10,000

1000

MAX186/MAX188

FAST POWER-DOWN

8 CHANNELS

1 CHANNEL

1 CHANNEL

10

100

2MHz EXTERNAL CLOCK

EXTERNAL COMPENSATION

50µs WAIT

1

0

50 100 150 200 250 300 350 400 450 500

CONVERSIONS PER CHANNEL PER SECOND

10

0

2k 4k 6k 8k 10k 12k 14k 16k 18k

CONVERSIONS PER CHANNEL PER SECOND

Figure 14a. MAX186 Supply Current vs. Sample Rate/Second,

FULLPD, 400kHz Clock

Lowest Power at Higher Throughputs

Figure 14b shows the power consumption with

external-reference compensation in fast power-down,

with one and eight channels converted. The external

4.7µF compensation requires a 50µs wait after power-up,

accomplished by 75 idle clocks after a dummy conver-

sion. This circuit combines fast multi-channel conversion

with lowest power consumption possible. Full

power-down mode may provide increased power sav-

ings in applications where the MAX186/MAX188 are

inactive for long periods of time, but where intermittent

bursts of high-speed conversions are required.

External and Internal References

The MAX186 can be used with an internal or external

reference, whereas an external reference is required for

the MAX188. Diode D1 shown in the Typical Operating

Circuit ensures correct start-up. Any standard signal

diode can be used. For both parts, an external refer-

ence can either be connected directly at the VREF ter-

minal or at the REFADJ pin.

An internal buffer is designed to provide 4.096V at

VREF for both the MAX186 and MAX188. The

MAX186’s internally trimmed 2.46V reference is

buffered with a gain of 1.678. The MAX188's buffer is

trimmed with a buffer gain of 1.638 to scale an external

2.5V reference at REFADJ to 4.096V at VREF.

MAX186 Internal Reference

The full-scale range of the MAX186 with internal reference

is 4.096V with unipolar inputs, and ±2.048V with bipolar

inputs. The internal reference voltage is adjustable to

±1.5% with the Reference-Adjust Circuit of Figure 17.

Figure 14b. MAX186/MAX188 Supply Current vs. Sample

Rate/Second, FASTPD, 2MHz Clock

3.0

2.5

2.0

1.5

1.0

0.5

0

0.0001 0.001 0.01 0.1

1

10

TIME IN SHUTDOWN (sec)

Figure 14c. Typical Power-Up Delay vs. Time in Shutdown

External Reference

With both the MAX186 and MAX188, an external refer-

ence can be placed at either the input (REFADJ) or the

output (VREF) of the internal buffer amplifier. The

REFADJ input impedance is typically 20kΩ for the

MAX186 and higher than 100kΩ for the MAX188, where

the internal reference is omitted. At VREF, the input

impedance is a minimum of 12kΩ for DC currents.

During conversion, an external reference at VREF must

be able to deliver up to 350µA DC load current and have

an output impedance of 10Ω or less. If the reference has

higher output impedance or is noisy, bypass it close to

the VREF pin with a 4.7µF capacitor.

18 ______________________________________________________________________________________

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