+2.7V to +5.25V, Low-Power, 4-Channel,

Serial 10-Bit ADCs in QSOP-16

Lowest Power at Higher Throughputs

Figure 13b shows the power consumption with

external-reference compensation in fast power-down,

with one and four channels converted. The external

4.7µF compensation requires a 75µs wait after power-up

with one dummy conversion. This circuit combines fast

multi-channel conversion with lowest power consumption

possible. Full power-down mode may provide increased

power

savings

in

applications

where

the

MAX1248/MAX1249 are inactive for long periods of time,

but where intermittent bursts of high-speed conversions

are required.

Internal and External References

The MAX1248 can be used with an internal or external

reference voltage, whereas an external reference is

required for the MAX1249. An external reference can

be connected directly at VREF or at the REFADJ pin.

An internal buffer is designed to provide 2.5V at VREF

for both the MAX1248 and the MAX1249. The

MAX1248’s internally trimmed 1.21V reference is

buffered with a gain of 2.06. The MAX1249’s REFADJ

pin is also buffered with a gain of 2.06 to scale an

external 1.25V reference at REFADJ to 2.5V at VREF.

Internal Reference (MAX1248)

The MAX1248’s full-scale range with the internal refer-

ence is 2.5V with unipolar inputs and ±1.25V with bipo-

lar inputs. The internal-reference voltage is adjustable

to ±1.5% with the circuit of Figure 15.

1

10

100

0.01

0.1

1

10

100

1k

CONVERSION RATE (Hz)

1 CHANNEL

CODE = 1010101000

4 CHANNELS

Figure 13a. MAX1248 Supply Current vs. Conversion Rate,

FULLPD

1

10

100

10,000

1000

0.1

10

1

100

1k

10k

100k

1M

CONVERSION RATE (Hz)

CODE = 1010101000

4 CHANNELS

1 CHANNEL

3.0

2.5

2.0

1.5

1.0

0.5

0

0

0.01

0.1

1

10

TIME IN SHUTDOWN (sec)

Figure 13b. MAX1248 Supply Current vs. Conversion Rate,

FASTPD

Figure 13c. Typical Reference-Buffer Power-Up Delay vs. Time

in Shutdown

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