MAX127 Datasheet, PDF (14/16 Pages) Maxim Integrated Products – Multirange, +5V, 12-Bit DAS with 2-Wire Serial Interface

Multirange, +5V, 12-Bit DAS with
2-Wire Serial Interface
MAX127
MAX128
REF
A_V = 1.638
REFADJ
10k
2.5V
C_REF
4.7µF
0.01µF
+5V
100k
24k
510k
0.01µF
REFADJ
MAX127
MAX128
Figure 11a. Internal Reference
MAX127
MAX128
REF
A_V = 1.638
REFADJ
10k
2.5V
4.096V
C_REF
4.7µF
V_DD
Figure 11b. External Reference, Reference at REF
MAX127
MAX128
REF
A_V = 1.638
10k
REFADJ
2.5V
C_REF
4.7µF
2.5V
0.01µF
Figure 11c. External Reference, Reference at REFADJ
Figure 12. Reference-Adjust Circuit
To power-up from a software initiated power-down, a
START condition followed by the correct slave address
must be received (with R/W = 0). The MAX127/MAX128
power-up after receiving the next bit.
For hardware-controlled power-down (FULLPD), pull
SHDN low. When hardware shutdown is asserted, it
becomes effective immediately and any conversion in
progress is aborted.
Choosing Power-Down Modes
The bandgap reference and reference buffer remain
active in STBYPD mode, maintaining the voltage on the
4.7µF capacitor at REF. This is a “DC” state that does
not degrade after standby power-down of any duration.
In FULLPD mode, only the bandgap reference is active.
Connect a 33µF capacitor between REF and AGND to
maintain the reference voltage between conversions
and to reduce transients when the buffer is enabled
and disabled. Throughput rates down to 1ksps can be
achieved without allotting extra acquisition time for ref-
erence recovery prior to conversion. This allows con-
version to begin immediately after power-down ends. If
the discharge of the REF capacitor during FULLPD
exceeds the desired limits for accuracy (less than a
fraction of an LSB), run a STBYPD power-down cycle
prior to starting conversions. Take into account that the
reference buffer recharges the bypass capacitor at an
80mV/ms slew rate, and add 50µs for settling time.
Auto-Shutdown
Selecting STBYPD on every conversion automatically
shuts the MAX127/MAX128 down after each conversion
without requiring any start-up time on the next conversion.
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