MAX148ACAP(1998) Просмотр технического описания (PDF) - Maxim Integrated

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производитель

MAX148ACAP
(Rev.:1998)

+2.7V to +5.25V, Low-Power, 8-Channel, Serial 10-Bit ADCs

Maxim Integrated 

+2.7V to +5.25V, Low-Power, 8-Channel,

Serial 10-Bit ADCs

Table 7. Full Scale and Zero Scale

UNIPOLAR MODE

Full Scale

Zero Scale

VREF + COM

COM

Positive

Full Scale

VREF / 2

+ COM

BIPOLAR MODE

Zero

Scale

COM

Negative

Full Scale

-VREF / 2

+ COM

OUTPUT CODE

011 . . . 111

011 . . . 110

000 . . . 010

000 . . . 001

000 . . . 000

111 . . . 111

111 . . . 110

111 . . . 101

FS = VREF + COM

2

ZS = COM

-FS = -VREF + COM

2

1LSB = VREF

1024

100 . . . 001

100 . . . 000

- FS

*COM VREF / 2

COM*

INPUT VOLTAGE (LSB)

+FS - 1LSB

Figure 18. Bipolar Transfer Function, Full Scale (FS) =

VREF / 2 + COM, Zero Scale (ZS) = COM

VREF, the DC input resistance is a minimum of 18kΩ.

During conversion, an external reference at VREF must

deliver up to 350µA DC load current and have 10Ω or

less output impedance. If the reference has a higher

output impedance or is noisy, bypass it close to the

VREF pin with a 4.7µF capacitor.

Using the REFADJ input makes buffering the external

reference unnecessary. To use the direct VREF input,

disable the internal buffer by tying REFADJ to VDD. In

power-down, the input bias current to REFADJ is typi-

cally 25µA (MAX149) with REFADJ tied to VDD. Pull

REFADJ to AGND to minimize the input bias current in

power-down.

+3V

R* = 10Ω

SUPPLIES

+3V GND

VDD

AGND

COM DGND

*OPTIONAL

MAX148

MAX149

+3V DGND

DIGITAL

CIRCUITRY

Figure 19. Power-Supply Grounding Connection

Transfer Function

Table 7 shows the full-scale voltage ranges for unipolar

and bipolar modes.

The external reference must have a temperature coeffi-

cient of 20ppm/°C or less to achieve accuracy to within

1LSB over the 0°C to +70°C commercial temperature

range.

Figure 17 depicts the nominal, unipolar input/output

(I/O) transfer function, and Figure 18 shows the bipolar

input/output transfer function. Code transitions occur

halfway between successive-integer LSB values.

Output coding is binary, with 1LSB = 2.44mV (2.500V /

1024) for unipolar operation, and 1LSB = 2.44mV

[(2.500V / 2 - -2.500V / 2) / 1024] for bipolar operation.

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