Rainbow Electronics MAX1035 - Manual (Page 15)

Analog Input Circuitry
The analog inputs can be individually configured for
either differential or single-ended conversions by writing
the associated analog input configuration byte (Table 2).
The analog input signal source must be capable of dri-
ving the ADC’s 6k
Ω input resistance (Figure 6).
Figure 6 shows the simplified analog input circuit. The
analog inputs are ±6V fault tolerant and are protected
by back-to-back diodes. The summing junction voltage,
V
SJ , is a function of the channel’s input common-mode
voltage:
As a result, the analog input impedance is relatively
constant over the input voltage as shown in Figure 5.
Single-ended conversions are internally referenced to
AGND1 (Tables 3 and 4). In differential mode, IN+ and
IN- are selected according to Tables 3 and 5. When con-
figuring differential channels, the differential pair follows
the analog configuration byte for the positive channel.
For example, to configure CH2 and CH3 for a ±V
REF dif-
ferential conversion, set the CH2 analog configuration
byte for a differential conversion with the ±V
REF range
(1010 1100). To initiate a conversion for the CH2 and
CH3 differential pair, issue the command 1010 0000.
Analog Input Bandwidth
The MAX1034/MAX1035 input-tracking circuitry has a
1.5MHz small-signal bandwidth. The 1.5MHz input
bandwidth makes it possible to digitize high-speed
transient events. Harmonic distortion increases when
digitizing signal frequencies above 15kHz as shown in
the THD, -SFDR vs. Analog Input Frequency plot in the
Typical Operating Characteristics.
Analog Input Range and Fault Tolerance
Figure 7 illustrates the software-selectable single-
ended analog input voltage range that produces a valid
digital output. Each analog input channel can be inde-
pendently programmed to one of seven single-ended
input ranges by setting the R[2:0] control bits with
DIF/SGL = 0.
V
R
R R
V
R
R R
V
SJ CM
. =
+

 

Ч + +
+

 
 
 

Ч
1
1 2
2 375 1
1
1 2
MAX1034/MAX1035
8-/4-Channel, ±V
REF
Multirange Inputs,
Serial 14-Bit ADCs
______________________________________________________________________________________ 15
CS
SCLK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
DIN S C2 C1 C0 0 0 0 0
ANALOG INPUT
TRACK AND HOLD*
DOUT B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 X X
BYTE 1 BYTE 2 BYTE 3 BYTE 4
SSTRB
HOLD TRACK HOLD
HIGH
IMPEDANCE
t ACQ
*TRACK AND HOLD TIMING IS CONTROLLED BY SCLK.
f SAMPLE
≈ f
SCLK / 32
SAMPLING INSTANT
HIGH
IMPEDANCE
Figure 2. External Clock-Mode Conversion (Mode 0)