MAX1156 Datasheet, PDF (9/15 Pages) Maxim Integrated Products – 14-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range

14-Bit, 135ksps, Single-Supply ADCs with
Bipolar Analog Input Range
MAX1156
R2
AIN
161Ω
R3
R1
3.4kΩ
TRACK
S1
C_HOLD
30pF
HOLD
TRACK
T/H OUT
HOLD
S2
S1, S2 = T/H SWITCH
S3 = POWER-DOWN
(MAX1158/MAX1174 ONLY)
REF
MAX1158/MAX1174
R2
AIN
161Ω
R1
3.4kΩ
TRACK
S1
C_HOLD
30pF
R3
S3
POWER-
DOWN
HOLD
TRACK
R2 = 7.85kΩ (MAX1158)
OR 3.92kΩ (MAX1156/MAX1174)
R3 = 5.45kΩ (MAX1158)
OR 17.79kΩ (MAX1156/MAX1174)
T/H OUT
HOLD
S2
Figure 4. Equivalent Input Circuit
Selecting Standby or Shutdown Mode
The MAX1156/MAX1158/MAX1174 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, elimi-
nating 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 (C_REFADJ = 0.1µF,
C_REF = 10µF) to power up and settle from shutdown.
The state of R/C at the second falling edge of CS
selects which power-down mode the MAX1156/
MAX1158/MAX1174 enter upon conversion completion.
Holding R/C low causes the MAX1156/MAX1158/
MAX1174 to enter standby mode. The reference and
buffer are left on after the conversion completes. R/C
high causes the MAX1156/MAX1158/MAX1174 to enter
shutdown mode and power down the reference and
buffer after conversion (see Figures 5 and 6). Set the
voltage at R/C high during the second falling edge of
CS to realize the lowest current 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 MAX1156/MAX1158/MAX1174 to exit stand-
by mode and begin acquisition. The reference and ref-
erence 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 14-bit accuracy,
allow 12ms (C_REFADJ = 0.1µF, C_REF = 10µF) for the
internal reference to wake up.
Internal and External Reference
Internal Reference
The internal reference of the MAX1156/MAX1158/
MAX1174 is internally buffered to provide +4.096V out-
put 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 reference. The input impedance of REFADJ
is nominally 5kΩ. Use the circuit of Figure 7 to adjust
the internal reference to ±1.5%.
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