+2 .7 V t o +5 .2 5 V, Lo w -P o w e r, 4 -Ch a n n e l,
S e ria l 1 0 -Bit ADCs in QS OP -1 6
8/MAX1249
100
10
1
10,000
R
= ∞
R
= ∞
LOAD
LOAD
CODE = 1010101000
CODE = 1010101000
1000
100
10
4 CHANNELS
4 CHANNELS
1 CHANNEL
1 CHANNEL
1
0.01
0.1
1
10
100
1k
0.1
1
10 100 1k 10k 100k 1M
CONVERSION RATE (Hz)
CONVERSION RATE (Hz)
Figure 13a. MAX1248 Supply Current vs. Conversion Rate,
FULLPD
Figure 13b. MAX1248 Supply Current vs. Conversion Rate,
FASTPD
Lowest Power at Higher Throughputs
Fig ure 13b s hows the p owe r c ons ump tion 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
p owe r s a ving s in a p p lic a tions whe re the
MAX1248/MAX1249 are inactive for long periods of time,
but where intermittent bursts of high-speed conversions
are required.
3.0
2.5
2.0
1.5
1.0
In t e rn a l a n d Ex t e rn a l Re fe re n c e s
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.
0.5
0
0
0.01
0.1
1
10
TIME IN SHUTDOWN (sec)
An internal buffer is designed to provide 2.5V at VREF
for b oth the MAX1248 a nd the MAX1249. The
MAX1248’s inte rna lly trimme d 1.21V re fe re nc e 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.
Figure 13c. Typical Reference-Buffer Power-Up Delay vs. Time
in Shutdown
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.
______________________________________________________________________________________ 17
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
