Power-Down Modes

Select standby mode or shutdown mode with the R/C

bit during the second falling edge of CS (see the

Selecting Standby or Shutdown Mode section). The

MAX1177 automatically enters either standby mode

(reference and buffer on) or shutdown (reference and

buffer off) after each conversion, depending on the sta-

tus of R/C during the second falling edge of CS.

Internal Clock

The MAX1177 generates an internal conversion clock to

free the µP from the burden of running the SAR conver-

hold mode (second falling edge of CS) to end-of-con-

version (EOC) falling is 4.7µs (max).

Applications Information

Starting a Conversion

CS and R/C control acquisition and conversion in the

MAX1177 (Figure 2). The first falling edge of CS powers

up the device and puts it in acquire mode if R/C is low.

The convert start is ignored if R/C is high. The device

needs at least 12ms for the internal reference to wake

Selecting Standby or Shutdown Mode

The MAX1177 has 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 refer-

ence and reference buffer after completing a conver-

sion. The reference and reference buffer require a

minimum of 12ms to power up and settle from shut-

The state of R/C at the second falling edge of CS

selects which power-down mode the MAX1177 enters

upon conversion completion. Holding R/C low causes

the device to enter standby mode. The reference and

buffer are left on after the conversion completes. R/C

high causes the MAX1177 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.

16-Bit, 135ksps, Single-Supply ADC

with to 10V Input Range

8

_______________________________________________________________________________________

S1, S2 = T/H SWITCH

R2 = 3.92k

Ω

R3 = 17.79k

Ω

S2

S1

AIN

R1

3.4k

Ω

R3

17.79k

Ω

R2

3.92k

Ω

T/H OUT

HOLD

HOLD

TRACK

TRACK

30pF

161

Ω

MAX1177

Figure 4. Equivalent Input Circuit

D0–D7

OR

D8–D15

µP DATA

BUS

AGND DGND

+5V ANALOG

+5V DIGITAL

ANALOG INPUT

AIN

HBEN

EOC

CS

R/C

REF

REFADJ

HIGH

BYTE

LOW

BYTE

10

µF

0.1

µF

0.1

µF

0.1

µF

MAX1177

Figure 3. Typical Operating Circuit for the MAX1177