MAX1106 Datasheet, PDF(14/16 Page) Maxim Integrated Products – Single-Supply, Low-Power, Serial 8-Bit ADCs

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MAX1106 Datasheet, PDF (14/16 Pages) Maxim Integrated Products – Single-Supply, Low-Power, Serial 8-Bit ADCs

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Single-Supply, Low-Power,

Serial 8-Bit ADCs

When operating at speeds below the maximum sam-

pling rate, the MAX1106/MAX1107âs power-down mode

can save considerable power by placing the converter

in a low-current shutdown state between conversions.

Pull SHDN low after the conversion byte has been read

to shut down the device completely.

CONVST should remain low most of the time and tog-

gled high for 1Âµs (100Âµs max) for the autozero adjust-

ment. An external reference is recommended for best

accuracy when using the shutdown feature. This

requires only 20Âµs for the internal biasing circuit to sta-

bilize before starting a new conversion. Alternatively,

the internal reference can be used, but additional time

is required for the reference to stabilize (when

bypassed by a 1ÂµF capacitor; at data rates above

1ksps, the reference stabilizes within 1LSB in 200Âµs). If

the reference is completely discharged it requires

12ms to settle. No conversions should be performed

until the reference voltage has stabilized.

Internal or External Voltage Reference

An external reference between 1V and VDD should be

connected directly at the REFIN pin. To use the internal

reference, connect REFOUT directly to REFIN and

bypass REFOUT with a 1ÂµF capacitor. 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

1kâ¦ or less at the conversion clock frequency. If the

reference has higher output impedance or is noisy,

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

The internal reference is active as long as SHDN is high

and powers down when SHDN is low.

OUTPUT CODE

11111111

11111110

11111101

FULL-SCALE

TRANSITION

FS = VREFIN + VIN-

1LSB = VREFIN

256

00000011

00000010

00000001

00000000

(IN-)

INPUT VOLTAGE (LSB)

Figure 9. Input/Output Transfer Function

FS - 1LSB

Transfer Function

Figure 9 depicts the input/output transfer function.

Code transitions occur at integer LSB values. Output

coding is binary; with a 2.048V reference 1LSB = 8mV

(VREFIN / 256). For single-ended operation connect IN-

to GND. Full-scale is achieved at VIN+ = VREFIN - 1LSB.

For pseudo-differential operation the VIN- voltage range

is from GND to VDD, where full-scale is achieved at

VIN+ = VREFIN + VIN- - 1LSB. VIN+ should not be higher

than VDD + 50mV. Negative input voltages are invalid

and give a zero output code. Voltages greater than full-

scale give an all ones output code.

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