MAX1497 Datasheet, PDF(12/33 Page) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers and μC Interface

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MAX1497 Datasheet, PDF (12/33 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers and μC Interface

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3.5- and 4.5-Digit, Single-Chip ADCs with LED

Drivers and ÂµC Interface

AVDD DVDD

SCLK DIN DOUT CS

ISET VLED

MAX1499

+2.5V

AIN+

AIN-

INPUT

BUFFERS

REF+

REF-

-2.5V

SERIAL I/O AND CONTROL

BINARY-TO-

ADC

BCD

CONVERTERS

2.048V

BANDGAP

REFERENCE

OSCILLATOR

CLOCK

+2.5V

-2.5V

A = 1.22

CHARGE

PUMP

LED

DRIVER

CONTROL

EOC

SEG1

SEGF

SEGDP

DIG0

DIG4

LED_EN

GLED

CLK

2.048V

GND

Figure 1. MAX1499 Functional Diagram

Digital Filtering

The MAX1497/MAX1499 contain an on-chip digital low-

pass 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 MAX1497/MAX1499 have 25% overrange capabili-

ty built into the modulator and digital filter. The digital fil-

ter is optimized for the fCLK equal to 4.9152MHz. Other

clock frequencies can be used; however, 50Hz/60Hz

noise rejection decreases. 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

sinï£«ï£ï£¬

Ïf

ï£¶

ï£¸ï£·

ï£¶

ï£¸ï£·

ï£¹4

ï£º

ï£»ï£º

VNEG

LOWBATT

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

data rate = 5Hz.

Filter Characteristics

Figure 2 shows the filter frequency response. The

SINC4 characteristic -3dB cutoff frequency is 0.228

times the first notch frequency (5Hz). The oversampling

ratio (OSR) for the MAX1497 is 128 and the OSR for the

MAX1499 is 1024.

The output data rate for the digital filter corresponds to

the positioning of the first notch of the filterâs frequency

response. The notches of the SINC4 filter are repeated

at multiples of the first notch frequency. The SINC4 filter

provides an attenuation of better than 100dB at these

notches. For example, 50Hz is equal to 10 times the

first notch frequency and 60Hz is equal to 12 times the

first notch frequency.

For large step changes at the input, allow a settling

time of 800ms before valid data is read.

Clock Modes

Configure the MAX1497/MAX1499 to use either the

internal oscillator or an externally applied clock to drive

the modulator and filter. Set the EXTCLK bit in the con-

trol register to zero to put the device in internal-clock

mode. Set the EXTCLK bit to one to put the device in

12 ______________________________________________________________________________________

▷