LTC2360/LTC2361/LTC2362

15

236012f

APPLICATIONS INFORMATION

ACHIEVING MICROPOWER PERFORMANCE

With typical operating currents of 0.5mA, 0.75mA and

1.1mA for the LTC2360/LTC2361/LTC2362 and automati-

cally entering sleep mode right after a conversion, these

devices achieve extremely low power consumption over

a wide range of sample rates (see Figure 11). The sleep

mode allows the supply current to drop with reduced

sample rate. Several things must be taken into account

to achieve such low power consumption.

Minimize Power Consumption in Sleep Mode

The LTC2360/LTC2361/LTC2362 enter sleep mode after

each conversion if CONV remains high and draw only

leakage current (see Figure 10). If the CONV input is not

running rail-to-rail, the input logic buffer will draw current.

This current may be large compared to the typical supply

current. To obtain the lowest supply current, bring the CONV

After the conversion with CONV staying high, the converter

is in sleep mode and draws only leakage current. The status

of the SCK input has no effect on supply current during

this time. For the best performance, hold SCK either high

or low while the ADC is converting.

Minimize the Device Active Time

In systems that have significant time between conversions,

the ADC draws a minimal amount of power. Figures 12

and 13 show two ways to minimize the amount of time

the ADC draws power. In Figure 12, the ADC draws power

the time. The conversion results are available at the next

CONV falling edge. In Figure 13, the ADC draws twice the

power than that in Figure 12, but the conversion results

SCK available in the system to shorten data transfer time,

SDO Loading

Capacitive loading on the digital output can increase power

consumption. A 100pF capacitor on the SDO pin can add

more than 50μA to the supply current at a 200kHz clock

frequency. An extra 50μA or so of current goes into charg-

ing and discharging the load capacitor. The same goes for

digital lines driven at a high frequency by any logic. The

C • V • f currents must be evaluated with the troublesome

ones minimized.

Figure 11. Supply Current vs Sample Rate

RECOMMENDED HIGH OR LOW

Hi-Z STATE

236012 F12

B11

CONV

SCK

SDO

12

3

4

9

10

11

12

B10

B9

B3

B2

B1

B0

SAMPLING INPUT AND

TRANSFERRING DATA

EXECUTING A CONVERSION AND PUTTING

THE DEVICE INTO SLEEP MODE

SLEEP MODE

Figure 12. Minimize the Time When the Device Draws Power, While the Conversion Results are Available After the Device Wakes Up

SAMPLE RATE (ksps)

236012 TA01b

1200

1000

800

400

600

200

0

1

100

1000

10

LTC2361

LTC2362

LTC2360