MAX1447 Datasheet, PDF(11/24 Page) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers

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MAX1447 Datasheet, PDF (11/24 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers

◁

3.5- and 4.5-Digit, Single-Chip ADCs

with LED Drivers

AVDD DVDD

ISET VLED

+2.5V

TIMING

AIN+

AIN-

INPUT

BUFFERS

REF+

BINARY-TO-

ADC

BCD

CONVERTERS

LED

DRIVER

REF-

OSCILLATOR

CLOCK

-2.5V

+2.5V

-2.5V

2.048V

BANDGAP

REFERENCE

A = 1.22

CHARGE

PUMP

MAX1447

MAX1498

SEG1

SEGF

SEGDP

DIG0

DIG4

LED_EN

GLED

CLK

DPON

DPSET1

DPSET2

RANGE

PEAK

HOLD

GND

VNEG

Figure 1. MAX1447/MAX1498 Functional Diagram

Modulator

The MAX1447/MAX1496/MAX1498 perform analog-to-

digital conversions using a single-bit, 3rd-order, sigma-

delta modulator. The sigma-delta modulator converts

the input signal into a digital pulse train whose average

duty cycle represents the digitized signal information.

The modulator quantizes the input signal at a much

higher sample rate than the bandwidth of the input.

The MAX1447/MAX1496/MAX1498 modulator provides

3rd-order frequency shaping of the quantization noise

resulting from the single-bit quantizer. The modulator is

fully differential for maximum signal-to-noise ratio and

minimum susceptibility to power-supply noise. A single-

bit data stream is then presented to the digital filter to

remove the frequency-shaped quantization noise.

Digital Filtering

The MAX1447/MAX1496/MAX1498 contain an on-chip

digital lowpass filter that processes the data stream

from the modulator using a SINC4 response:

ï£« sin(x) ï£¶ 4

ï£ï£¬ x ï£¸ï£·

The SINC4 filter has a settling time of four output data

periods (4 x 200ms).

The MAX1447/MAX1496/MAX1498 have 25% over-

range capability built into the modulator and digital fil-

ter. The digital filter is optimized for the fCLK equal to

4.9152MHz. The frequency response of the SINC4 filter is

calculated as follows:

H(z)

ï£®

ï£¯

ï£°ï£¯

Z-N)

Z-1)

ï£¹4

ï£º

ï£»ï£º

H(f)

ï£®

ï£¯

ï£°ï£¯

sinï£«ï£ï£¬NÏ

ï£«

sinï£ï£¬

Ïf

ï£¶

ï£¸ï£·

ï£¶

ï£¸ï£·

ï£¹4

ï£º

ï£»ï£º

where N is the oversampling ratio, and fm = N x output

data rate = 5Hz.

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