MAX1108_03 Datasheet, PDF(17/20 Page) Maxim Integrated Products – Single-Supply, Low-Power, 2-Channel, Serial 8-Bit ADCs

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

MAX1108_03 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – Single-Supply, Low-Power, 2-Channel, Serial 8-Bit ADCs

◁

Single-Supply, Low-Power,

2-Channel, Serial 8-Bit ADCs

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

1Âµs 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-

supply voltage, VDD / 2, which is internally generated.

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

select this configuration. This allows the user to monitor

the condition of a battery providing VDD. The reference

voltage must be larger than VDD / 2 for this mode of

operation to work properly. From the result of conver-

sion (CODE), VDD is determined as follows:

VDD = CODE Â· VREF / 128.

Power-On Configuration

When power is first applied, the MAX1108/MAX1109âs

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 20Âµs 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 perform-

ing a second conversion once the reference is settled. No

conversions should be considered correct until the refer-

ence voltage (internal or external) has stabilized.

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.

Table 4. Power-Down Modes of the

MAX1108/MAX1109

BIT 2âBIT 0 OF

CONTROL BYTE

I/EREF REFSHDN SHDN

OPERATING MODE

Device Active/Internal

Reference Active

Device Active; Internal refer-

ence powered down after con-

version, powered up at next

start bit.

Device Active/External

Reference Mode

Device and internal reference

0 powered down after conversion,

powered up at next start bit.

Device powered down after

each conversion, powered up

at next start bit. External

Reference Mode.

0 Reserved. Do not use.

X = Donât care

The first logical 1 clocked into DIN after CS falls powers

up the MAX1108/MAX1109 (20Âµs 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:

in unipolar mode, the input range is from 0 to VREF; in

bipolar mode, the input range spans RI Â±VREF / 2 with

RI = VREF / 2.

______________________________________________________________________________________ 17

▷