Table 1a. Unipolar Full Scale and Zero

Scale

5V, 8-Channel, Serial, 12-Bit ADCs

with 3V Digital Interface

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11

Input Bandwidth

The ADC’s input tracking circuitry has a 4.5MHz

small-signal bandwidth. Therefore it is possible to digi-

tize high-speed transient events and measure periodic

signals with bandwidths exceeding the ADC’s sampling

rate by using undersampling techniques. To avoid

high-frequency signals being aliased into the frequency

band of interest, anti-alias filtering is recommended.

Analog Input Range and Input Protection

Internal protection diodes, which clamp the analog

age. However, for accurate conversions near full scale,

If the analog input exceeds 50mV beyond the sup-

plies, do not forward bias the protection diodes of

off-channels more than 2mA.

The full-scale input voltage depends on the voltage at

REF (Tables 1a and 1b).

Quick Look

Use the circuit of Figure 5 to quickly evaluate the

MAX1202/MAX1203’s analog performance. The

MAX1202/MAX1203 require a control byte to be written

to DIN before each conversion. Tying DIN to +3V feeds

in control byte $FF hex, which triggers single-ended

unipolar conversions on CH7 in external clock mode

without powering down between conversions. In exter-

nal clock mode, the SSTRB output pulses high for one

clock period before the most significant bit of the 12-bit

conversion result shifts out of DOUT. Varying the ana-

log input to CH7 alters the sequence of bits from

DOUT. A total of 15 clock cycles per conversion is

required. All SSTRB and DOUT output transitions occur

on SCLK’s falling edge.

How to Start a Conversion

Clocking a control byte into DIN starts conversion on

the MAX1202/MAX1203. With CS low, each rising edge

on SCLK clocks a bit from DIN into the MAX1202/

MAX1203’s internal shift register. After CS falls, the first

logic “1” bit defines the control byte’s MSB. Until this

first “start” bit arrives, any number of logic “0” bits can

be clocked into DIN with no effect. Table 2 shows the

control-byte format.

The MAX1202/MAX1203 are fully compatible with

SPI/MICROWIRE devices. For SPI, select the correct

clock polarity and sampling edge in the SPI control reg-

isters: set CPOL = 0 and CPHA = 0. MICROWIRE and

SPI both transmit and receive a byte at the same time.

Using the

Typical Operating Circuit, the simplest soft-

ware interface requires only three 8-bit transfers to per-

form a conversion (one 8-bit transfer to configure the

ADC, and two more 8-bit transfers to clock out the

12-bit conversion result).

Table 1b. Bipolar Full Scale, Zero Scale,

and Negative Full Scale

REFERENCE

External

ZERO

SCALE

0V

0V

at REFADJ

at REF

FULL SCALE

0V

Internal

+4.096V

x A*

NEGATIVE

FULL SCALE

-4.096V / 2

x A*

0V

0V

+4.096V / 2

FULL SCALE

0V

ZERO

SCALE

at

REFADJ

External

REFERENCE

Internal

at REF

*

A = 1.68 for the MAX1202, 1.64 for the MAX1203.

*

A = 1.68 for the MAX1202, 1.64 for the MAX1203.