MAX1280 Datasheet, PDF (18/24 Pages) Maxim Integrated Products – 400ksps/300ksps, Single-Supply, Low-Power, 8-Channel, Serial 12-Bit ADCs with Internal Reference

400ksps/300ksps, Single-Supply, Low-Power, 8-Channel,
Serial 12-Bit ADCs with Internal Reference
power consumption using the specified power-down
mode, with the internal reference and the maximum
clock speed. The clock speed in FASTPD or REDP
should be limited to 4.8MHz for the MAX1280/
MAX1281. FULLPD mode may provide increased power
2.5
NORMAL OPERATION
2.0
REDP
FASTPD
1.5
1.0
MAX1281, V_DD1 = V_DD2 = 3.0V
C_LOAD = 20pF
CODE = 101010000000
0.5
0 50 100 150 200 250 300 350
SAMPLING RATE (sps)
Figure 11. Average Supply Current vs. Sampling Rate (Using
REPD, FASTPD, and Normal Operation and Internal Reference)
savings in applications where the MAX1280/
MAX1281 are inactive for long periods of time, but
where intermittent bursts of high-speed conversions are
required.
Internal and External References
The MAX1280/MAX1281 can be used with an internal
or external reference. An external reference can be
connected directly at REF or at the REFADJ pin.
An internal buffer is designed to provide 2.5V at REF for
both the MAX1280/MAX1281. The internally trimmed
1.22V reference is buffered with a gain of +2.05V/V.
Internal Reference
The MAX1280/MAX1281’s full-scale range with the inter-
nal reference is 2.5V for unipolar inputs and ±1.25V for
bipolar inputs. The internal reference voltage is
adjustable to ±100mV with the circuit of Figure 13.
External Reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the internal reference-
buffer amplifier. The REFADJ input impedance is typical-
ly 17kΩ. At REF, the DC input resistance is a minimum of
WAIT 2ms (10 x RC)
1
00
1
10
1
00
1
DIN
FULLPD
REDP
FULLPD
RE FADJ
1.22V
DUMMY CONVERSION
1.22V
0V
γ = RC = 17kΩ x 0.01µF
2.5V
2.5V
REF
0V
I_VDD1 + I_VDD2
2.5mA
2.5mA
1.3mA OR 0.9mA
0mA
2.5mA
0mA
Figure 12a. Full Power-Down Timing
DIN
REF
I_VDD1 + I_VDD2
1
10
REDPD
2.5V (ALWAYS ON)
2.5mA
0.9mA
1
10
REDP
2.5mA
0.9mA
1
01
FASTPD
2.5mA
1.3mA
Figure 12b. Reduced-Power/Fast Power-Down Timing
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