MAX1111CE Datasheet, PDF(16/20 Page) Maxim Integrated Products – 2.7V, Low-Power, Multichannel, Serial 8-Bit ADCs

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MAX1111CE Datasheet, PDF (16/20 Pages) Maxim Integrated Products – 2.7V, Low-Power, Multichannel, Serial 8-Bit ADCs

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+2.7V, Low-Power, Multichannel,

Serial 8-Bit ADCs

Applications Information

Power-On Reset

When power is first applied, and if SHDN is not pulled

low, internal power-on reset circuitry activates the

MAX1110/MAX1111 in internal clock mode. SSTRB is

high on power-up and, if CS is low, the first logical 1 on

DIN is interpreted as a start bit. Until a conversion takes

place, DOUT shifts out zeros. No conversions should

be performed until the reference voltage has stabilized

(see Electrical Characteristics).

Power-Down

When operating at speeds below the maximum sam-

pling rate, the MAX1110/MAX1111âs automatic power-

down mode can save considerable power by placing

the converters in a low-current shutdown state between

conversions. Figure 13 shows the average supply cur-

rent as a function of the sampling rate.

Select power-down with PD1 of the DIN control byte

with SHDN high or high impedance (Table 3). Pull

SHDN low at any time to shut down the converters com-

pletely. SHDN overrides PD1 of the control byte.

Figures 14a and 14b illustrate the various power-down

sequences in both external and internal clock modes.

Software Power-Down

Software power-down is activated using bit PD1 of the

control byte. When software power-down is asserted, the

ADCs continue to operate in the last specified clock

mode until the conversion is complete. The ADCs then

power down into a low quiescent-current state. In internal

clock mode, the interface remains active, and conversion

results can be clocked out after the MAX1110/

MAX1111 have entered a software power-down.

The first logical 1 on DIN is interpreted as a start bit,

which powers up the MAX1110/MAX1111. If the DIN byte

contains PD1 = 1, then the chip remains powered up. If

PD1 = 0, power-down resumes after one conversion.

Table 5. Hard-Wired Power-Down and

Internal Reference State

SHDN

STATE

High Impedance

DEVICE

MODE

Enabled

Power-Down

INTERNAL

REFERENCE

Disabled

Enabled

Disabled

Hard-Wired Power-Down

Pulling SHDN low places the converters in hard-wired

power-down. Unlike software power-down, the conversion

is not completed; it stops coincidentally with SHDN being

brought low. SHDN also controls the state of the internal

reference (Table 5). Letting SHDN high impedance

enables the internal 2.048V voltage reference. When

returning to normal operation with SHDN high impedance,

there is a tRC delay of approximately 1MÎ© x CLOAD,

where CLOAD is the capacitive loading on the SHDN pin.

Pulling SHDN high disables the internal reference, which

saves power when using an external reference.

External Reference

An external reference between 1V and VDD should be

connected directly at the REFIN terminal. The DC input

impedance at REFIN is extremely high, consisting of

leakage current only (typically 10nA). During a conver-

sion, the reference must be able to deliver up to 20ÂµA

average load current and have an output impedance of

reference has higher output impedance or is noisy,

bypass it close to the REFIN pin with a 0.1ÂµF capacitor.

If an external reference is used with the MAX1110/

MAX1111, connect SHDN to VDD to disable the internal

reference and decrease power consumption.

1000

CLOAD = 60pF

CODE = 10101010

100

CLOAD = 30pF

CODE = 10101010

CLOAD = 30pF

CODE = 11111111

VDD = VREFIN = 3V

CLOAD AT DOUT AND SSTRB

SAMPLING RATE (ksps)

Figure 13. Average Supply Current vs. Sampling Rate

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