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 MAX1177 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

Internal and External Reference

Internal Reference

The internal reference of the MAX1177 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 reference. The

input impedance of REFADJ is nominally 5k

Ω. Use the

circuit in Figure 7 to adjust the internal reference to

±1.5%.

External Reference

An external reference can be placed at either the input

(REFADJ) or the output (REF) of the MAX1177’s internal

buffer amplifier. Using the buffered REFADJ input

makes buffering the external reference unnecessary.

The input impedance of REFADJ is typically 5k

Ω. The

internal buffer output must be bypassed at REF with a

10µF capacitor.

Directly drive REF using an external 3.8V to 4.2V refer-

ence. During conversion, the external reference must

be able to drive 100µA of DC load current and have an

output impedance of 10

Ω or less.

For optimal performance, buffer the reference through

an op amp and bypass REF with a 10µF capacitor.

Consider the MAX1177’s equivalent input noise (0.6

LSB) when choosing a reference.

16-Bit, 135ksps, Single-Supply ADC

with 0 to 10V Input Range

_______________________________________________________________________________________

9

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

+5V

68k

Ω

100k

Ω

150k

Ω

0.1

µF

REFADJ

MAX1177

Figure 7. MAX1177 Reference Adjust Circuit