Multirange, +5V, 8-Channel,

Serial 12-Bit ADCs

10

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Input Bandwidth

The ADC’s input small-signal bandwidth depends on the

selected input range and varies from 1.5MHz to 5MHz

(see Electrical Characteristics). The MAX1270B/

MAX1271B maximum sampling rate is 110ksps (100ksps

for the MAX1270A/MAX1271A). By using undersampling

techniques, it is possible to digitize high-speed transient

events and measure periodic signals with bandwidths

exceeding the ADC’s sampling rate.

To avoid high-frequency signals being aliased into the

frequency band of interest, anti-aliasing filtering is rec-

ommended.

Input Range and Protection

The MAX1270/MAX1271 have software-selectable input

ranges. Each analog input channel can be indepen-

dently programmed to one of four ranges by setting the

appropriate control bits (RNG, BIP) in the control byte

(Table 1). The MAX1270 has selectable input ranges

4 shows the equivalent input circuit.

A resistor network on each analog input provides

±16.5V fault protection for all channels. Whether or not

the channel is on, this circuit limits the current going

into or out of the pin to less than 2mA. This provides an

added layer of protection when momentary overvolt-

ages occur at the selected input channel, when a neg-

ative signal is applied to the input, and when the device

is configured for unipolar mode. The overvoltage pro-

tection is active even if the device is in power-down

Digital Interface

The MAX1270/MAX1271 feature a serial interface that is

fully compatible with SPI/QSPI and MICROWIRE devices.

For SPI/QSPI, set CPOL = 0, CPHA = 0 in the SPI control

registers of the microcontroller. Figure 5 shows detailed

serial-interface timing information. See Table 1 for details

on programming the input control byte.

CS

SCLK

DIN

DOUT

Figure 5. Detailed Serial-Interface Timing

R3

5.12k

Ω

R2

R1

CH_

S1

S2

S3

S4

BIPOLAR

UNIPOLAR

VOLTAGE

REFERENCE

T/H

OUT

HOLD

TRACK

TRACK

HOLD

OFF

ON

S1 = BIPOLAR/UNIPOLAR SWITCH

S2 = INPUT MUX SWITCH

S3, S4 = T/H SWITCH

R1 = 12.5k

Ω (MAX1270)

or 5.12k

Ω (MAX1271)

R2 = 8.67k

Ω (MAX1270)

or

∞ (MAX1271)

Figure 4. Equivalent Input Circuit