ference between the sampled positive and negative

input voltages is converted. The time required for the

T/H to acquire an input signal is determined by how

quickly its input capacitance is charged. The required

acquisition time lengthens as the input signal’s source

minimum time needed for the signal to be acquired. It is

calculated by the following equation:

where

Ω, which is the equivalent differential analog

input resistance.

input capacitance.

impedance below 400

Ω does not significantly affect the

ADC’s AC performance.

Analog Input Bandwidth

The ADC’s input-tracking circuitry has a 4MHz full-

power bandwidth, making it possible to digitize high-

speed transient events and measure periodic signals

with bandwidths exceeding the ADC’s sampling rate by

using undersampling techniques.

Use anti-alias filtering to avoid high-frequency signals

being aliased into the frequency band of interest.

Analog Input Range and Protection

The MAX1391/MAX1394 produce a digital output that

corresponds to the analog input voltage as long as the

analog inputs are within their specified range. When

operating the MAX1391 in unipolar mode (UNI/BIP = 1),

the specified differential analog input range is from 0 to

Internal protection diodes confine the analog input volt-

age within the region of the analog power input rails

bias the internal protection diodes. In this situation, limit

the forward diode current to less than 50mA to avoid

damage to the MAX1391/MAX1394.

Output Data Format

Figures 8, 9, and 10 illustrate the conversion timing for

the MAX1391/MAX1394. Twelve SCLK cycles are

required to read the conversion result and data on

DOUT transitions on the falling edge of SCLK. The con-

version result contains 4 zeros, followed by 8 data bits

with the data in MSB-first format. For the MAX1391, data

is straight binary for unipolar mode and two’s comple-

ment for bipolar mode. For the MAX1394, data is always

straight binary.

Transfer Function

Figure 5 shows the unipolar transfer function for the

MAX1391/MAX1394. Figure 6 shows the bipolar trans-

fer function for the MAX1391. Code transitions occur

halfway between successive-integer LSB values.

_______________________________________________________________________________________

9

1.5V to 3.6V, 416ksps, 1-Channel True-Differential/

2-Channel Single-Ended, 8-Bit, SAR ADCs

+

-

HOLD

TRACK

CIN+

REF

GND

DAC

CIN-

RIN+

RIN-

COMPARATOR

HOLD

HOLD

AIN2

AIN1 (AIN+)*

GND (AIN-)*

ANALOG

SIGNAL

SOURCE

MAX1391

MAX1394

(*INDICATES THE MAX1391)

Figure 4. Equivalent Input Circuit