MAX148BEPP View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX148BEPP

+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 + VCOM

VCOM

Positive Full Scale

VREF/2 + VCOM

BIPOLAR MODE

Zero Scale

VCOM

Negative Full Scale

- VREF/2 + VCOM

OUTPUT CODE

011 . . . 111

011 . . . 110

VFS

=

VREF

2

+ VCOM

ZS = COM

000 . . . 010

000 . . . 001

000 . . . 000

111 . . . 111

111 . . . 110

111 . . . 101

-VFS

=

-VREF

2

+ VCOM

1 LSB = VREF

1024

100 . . . 001

100 . . . 000

- FS

*VCOM ≥ VREF/2

COM*

INPUT VOLTAGE (LSB)

+FS - 1 LSB

+3V

R* = 10Ω

SUPPLIES

+3V GND

VDD

AGND

COM DGND

*OPTIONAL

MAX148

MAX149

+3V DGND

DIGITAL

CIRCUITRY

Figure 18. Bipolar Transfer Function, Full Scale (VFS) = VREF/2

+ VCOM, Zero Scale (ZS) = COM

deliver up to 350FA DC load current and have 10I or

less output impedance. If the reference has a higher

output impedance or is noisy, bypass it close to the VREF

pin with a 4.7FF 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

typically 25FA (MAX149) with REFADJ tied to VDD. Pull

REFADJ to AGND to minimize the input bias current in

power-down.

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 coef-

ficient of 20ppm/NC or less to achieve accuracy to within

1 LSB over the 0NC to +70NC 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 1 LSB = 2.44mV (2.500V/1024)

for unipolar operation, and 1 LSB = 2.44mV [(2.500V/2 -

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

  19

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