MAX11646 Datasheet, PDF(17/20 Page) Maxim Integrated Products – 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 10-Bit ADCs

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MAX11646 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 10-Bit ADCs

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2.7V to 3.6V and 4.5V to 5.5V, Low-Power,

1-/2-Channel, 2-Wire Serial, 10-Bit ADCs

Applications Information

Power-On Reset

The configuration and setup registers (Tables 1 and 2)

default to a single-ended, unipolar, single-channel conver-

sion on AIN0 using the internal clock with VDD as the refer-

ence. The memory contents are unknown after power-up.

Automatic Shutdown

Automatic shutdown occurs between conversions when

the MAX11646/MAX11647 are idle. All analog circuits

participate in automatic shutdown except the internal

reference due to its prohibitively long wake-up time.

When operating in external clock mode, a STOP, not-

acknowledge, or repeated START condition must be

issued to place the devices in idle mode and benefit

from automatic shutdown. A STOP condition is not nec-

essary in internal clock mode to benefit from automatic

shutdown because power-down occurs once all con-

version results are written to memory (Figure 10). When

using an external reference or VDD as a reference, all

analog circuitry is inactive in shutdown and supply cur-

rent is less than 0.5ÂµA (typ). The digital conversion

results obtained in internal clock mode are maintained

in memory during shutdown and are available for

access through the serial interface at any time prior to a

STOP or a repeated START condition.

When idle, the MAX11646/MAX11647 continuously wait

for a START condition followed by their slave address

(see the Slave Address section). Upon reading a valid

address byte the MAX11646/MAX11647 power up. The

internal reference requires 10ms to wake up, so when

using the internal reference it should be powered up

10ms prior to conversion or powered continuously.

Wake-up is invisible when using an external reference

or VDD as the reference.

Automatic shutdown results in dramatic power savings,

particularly at slow conversion rates and with internal

clock. For example, at a conversion rate of 10ksps, the

average supply current for the MAX11647 is 60ÂµA (typ)

and drops to 6ÂµA (typ) at 1ksps. At 0.1ksps the aver-

age supply current is just 1ÂµA, or a minuscule 3ÂµW of

power consumption (see Average Supply Current vs.

Conversion Rate (External Clock) in the Typical Operating

Characteristics).

Reference Voltage

SEL[2:0] of the setup byte (Table 1) control the reference

and the REF configuration (Table 6).

Internal Reference

The internal reference is 4.096V for the MAX11646 and

2.048V for the MAX11647. When REF is configured to be

an internal reference output (SEL[2:1] = 11), decouple

REF to GND with a 0.1ÂµF capacitor and a 2kÎ© series

resistor (see the Typical Operating Circuit). Once powered

up, the reference always remains on until reconfigured.

The internal reference requires 10ms to wake up and is

accessed using SEL0 (Table 6). When in shutdown, the

internal reference output is in a high-impedance state. The

reference should not be used to supply current for exter-

nal circuitry. The internal reference does not require an

external bypass capacitor and works best when left

unconnected (SEL1 = 0).

External Reference

The external reference can range from 1V to VDD. For

maximum conversion accuracy, the reference must be

able to deliver up to 40ÂµA and have an output imped-

put impedance or is noisy, bypass it to GND as close

as possible to REF with a 0.1ÂµF capacitor.

Table 6. Reference Voltage and REF Format

SEL2

SEL1

SEL0

REFERENCE VOLTAGE

VDD

External reference

Internal reference

X = Donât care.

*Preferred configuration for internal reference.

REF

Not connected

Reference input

Not connected*

Reference output

INTERNAL REFERENCE STATE

Always off

Always on

Always off

Always on

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