Datasheet

Selecting Standby or Shutdown Mode
The MAX1178/MAX1188 have a selectable standby or
low-power shutdown mode. In standby mode, the ADC’s
internal reference and reference buffer do not power
down between conversions, eliminating the need to wait
for the reference to power up before performing the next
conversion. Shutdown mode powers down the reference
and reference buffer after completing a conversion. The
reference and reference buffer require a minimum of
12ms to power up and settle from shutdown (C
REFADJ
=
0.1µF, C
REF
= 10µF).
The state of R/C at the second falling edge of CS
selects which power-down mode the MAX1178/
MAX1188 enter upon conversion completion. Holding
R/C low causes the MAX1178/MAX1188 to enter stand-
by mode. The reference and buffer are left on after the
conversion completes. R/C high causes the
MAX1178/MAX1188 to enter shutdown mode and
power-down the reference and buffer after conversion
(Figures 5 and 6). Set the voltage at R/C high during
the second falling edge of CS to realize the lowest cur-
rent operation.
Standby Mode
While in standby mode, the supply current is less than
3.7mA (typ). The next falling edge of CS with R/C low
causes the MAX1178/MAX1188 to exit standby mode
and begin acquisition. The reference and reference
buffer remain active to allow quick turn-on time.
Shutdown Mode
In shutdown mode, the reference and reference buffer
are shut down between conversions. Shutdown mode
reduces supply current to 0.5µA (typ) immediately after
the conversion. The next falling edge of CS with R/C low
causes the reference and buffer to wake up and enter
acquisition mode. To achieve 16-bit accuracy, allow
12ms for the internal reference to wake up (C
REFADJ
=
0.1µF, C
REF
= 10µF).
Internal and External Reference
Internal Reference
The internal reference of the MAX1178/MAX1188 is
internally buffered to provide +4.096V output at REF.
Bypass REF to AGND and REFADJ to AGND with 10µF
and 0.1µF, respectively. Sink or source current at
REFADJ to make fine adjustments to the internal refer-
ence. The input impedance of REFADJ is nominally
5kΩ. Use the circuit in Figure 7 to adjust the internal
reference to ±1.5%.
MAX1178/MAX1188
16-Bit, 135ksps, Single-Supply ADCs with
Bipolar Analog Input Range
_______________________________________________________________________________________ 9
S2
S1
AIN
R1
3.4kΩ
R3
R2
REF
T/H OUT
HOLD
HOLD
TRACK
TRACK
R2 = 7.85kΩ (MAX1188) OR 3.92kΩ (MAX1178)
R3 = 5.45kΩ (MAX1188) OR 17.79kΩ (MAX1178)
S1, S2 = T/H SWITCH
S3 = POWER-DOWN
C
HOLD
30pF
S3
POWER-
DOWN
161Ω
MAX1178/MAX1188
Figure 4. Equivalent Input Circuit
CS
R/C
EOC
REF AND
BUFFER
POWER
ACQUISITION CONVERSION
DATA
OUT
Figure 5. Selecting Standby Mode
CS
R/C
EOC
REF AND
BUFFER
POWER
ACQUISITION CONVERSION
DATA
OUT
Figure 6. Selecting Shutdown Mode