Rainbow Electronics MAX1083 User Manual

Page 15

MAX1082/MAX1083

300ksps/400ksps, Single-Supply, 4-Channel,

Serial 10-Bit ADCs with Internal Reference

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Software Power-Down

Software power-down is activated using bits PD1 and
PD0 of the control byte. When software power-down is
asserted, the ADC completes the conversion in
progress and powers down into the specified low-qui-
escent-current state (2µA, 0.9mA, or 1.3mA).

The first logic 1 on DIN is interpreted as a start bit and
puts the MAX1082/MAX1083 into its full-power mode.
Following the start bit, the data input word or control
byte also determines the next power-down state. For
example, if the DIN word contains PD1 = 0 and PD0 = 1, a
0.9mA power-down resumes after one conversion.
Table 4 details the four power modes with the corre-
sponding supply current and operating sections.

Hardware Power-Down

Pulling SHDN low places the converter in hardware
power-down. Unlike software power-down mode, the
conversion is not completed; it stops coincidentally with
SHDN being brought low. When returning to normal
operation—from SHDN, with an external reference—the
MAX1082/MAX1083 can be considered fully powered
up within 2µs of actively pulling SHDN high. When
using the internal reference, the conversion should be
initiated only when the reference has settled; its recov-
ery time is dependent on the external bypass capaci-
tors and the time between conversions.

Power-Down Sequencing

The MAX1082/MAX1083 auto power-down modes can
save considerable power when operating at less than
maximum sample rates. Figures 9 and 10 show the
average supply current as a function of the sampling
rate. The following sections discuss the various power-
down sequences. Other combinations of clock rates
and power-down modes may attain the lowest power
consumption in other applications.

Using Full Power-Down Mode

Full power-down mode (FULLPD) achieves the lowest
power consumption, up to 1000 conversions per chan-
nel per second. Figure 9a shows the MAX1083’s power
consumption for one- or four-channel conversions utiliz-
ing full power-down mode (PD1 = PD0 = 0), with the
internal reference and conversion controlled at the
maximum clock speed. A 0.01µF bypass capacitor at
REFADJ forms an RC filter with the internal 17k

Ω refer-

ence resistor, with a 170µs time constant. To achieve
full 10-bit accuracy, seven time constants or 1.2ms are
required after power-up if the bypass capacitor is fully
discharged between conversions. Waiting this 1.2ms
duration in fast power-down (FASTPD) or reduced-
power (REDP) mode instead of in full power-up can fur-
ther reduce power consumption. This is achieved by
using the sequence shown in Figure 11a.

Figure 9b shows the MAX1083’s power consumption for
one- or four-channel conversions utilizing FULLPD

400ns

(CLK = 6.4MHz)

IDLE

SCLK

DIN

SSTRB

DOUT

A/D STATE

ACQ

IDLE

CONVERSION

RB3

RB2

RB1

SEL

START

SEL

UNI/

BIP

SGL/

DIF

PD2 PD2

B9 B8

B6 B5

B1 B0

Figure 5. Single-Conversion Timing