In external clock mode, if CS is toggled before the cur-

rent conversion is complete, the current conversion is

terminated, and the next high bit clocked into DIN is

recognized as a new start bit. This can be useful in

extending acquisition time by selecting conversion on

the same channel with the second control byte (double-

clocking mode), effectively extending acquisition to 6

SCLKs. This technique is ideal if the analog input

source has high impedance, or if it requires more than

1µs to settle; it can also be used to allow the device

and the reference to settle when using power down-

modes (see

Power-Down Modes section).

__________Applications Information

Battery Monitoring Mode

This mode of operation samples and converts the mid-

Set SEL2 = SEL1 = SEL0 = 0 in the control byte to

select this configuration. This allows the user to monitor

operation to work properly. From the result of conver-

Power-On Configuration

When power is first applied, the MAX1108/MAX1109’s

reference is powered down and SHDN is not enabled.

The device needs to be configured by setting CS low

and writing the control byte. Conversion can be started

within 20µs if an external reference is used. When using

the internal reference, allow 12ms for the reference to

settle. This is done by first performing a configuration

conversion to power up the reference and then per-

forming a second conversion once the reference is set-

tled. No conversions should be considered correct until

the reference voltage (internal or external) has stabi-

lized.

Power-Down Modes

To save power, place the converter into low-current

power-down mode between conversions. Minimum

power consumption is achieved by programming

REFSHDN = 0 and SHDN = 0 in the input control byte

(Table 4). When software power-down is asserted, it

becomes effective only after the conversion. If the con-

trol byte contains REFSHDN = 0, then the reference will

turn off at the end of conversion. If SHDN = 0, then the

chip will power-down at the end of conversion (in this

mode I/EREF or REFSHDN should also be set to zero).

Table 4 lists the power-down modes of the MAX1108/

MAX1109.

The first logical 1 clocked into DIN after CS falls powers

up the MAX1108/MAX1109 (20µs required for the

device to power up). The reference is powered up only

if internal reference was selected during the previous

conversion. When the reference is powered up after

being disabled, consider the settling time before using

the result of conversion. Typically, 12ms are required

for the reference to settle from a discharge state; less

time may be considered if the external capacitor is not

discharged completely when exiting shutdown. In all

power-down modes, the interface remains active and

conversion results may be read. Use the double clock-

ing technique described in the

Data Framing section to

allow more time for the reference to settle before start-

ing a conversion after short power-down.

Voltage Reference

The MAX1108/MAX1109 operate from a single supply

and feature a software-controlled internal reference of

+2.048V (MAX1108) and +4.096V (MAX1109). The

device can operate with either the internal reference or

an external reference applied at the REF pin. See the

Power-Down Modes and Modes of Operation sections

for detailed instructions on reference configuration.

The reference voltage determines the full-scale range:

Single-Supply, Low-Power,

2-Channel, Serial 8-Bit ADCs

______________________________________________________________________________________

17

Table 4. Power-Down Modes of the

MAX1108/MAX1109

1

BIT 2–BIT 0 OF

CONTROL BYTE

1

1

0

1

1

1

0

0

0

1

X

1

0

0

1

0

X

REFSHDN

I/EREF

SHDN

OPERATING MODE

Device Active; Internal refer-

ence powered down after con-

version, powered up at next

start bit.

Device Active/Internal

Reference Active

Device and internal reference

powered down after conversion,

powered up at next start bit.

Device Active/External

Reference Mode

Reserved. Do not use.

Device powered down after

each conversion, powered up

at next start bit. External

Reference Mode.

X = Don’t care