
ISL26320, ISL26321, ISL26322, ISL26323, ISL26324, ISL26325, ISL26329
13
FN8273.1
September 5, 2013
Analog Inputs
Some members of the ISL26320, ISL26321, ISL26322,
ISL26323, ISL26324, ISL26325 and ISL26329 family feature a
fully differential input with a nominal full-scale range equal to
twice the applied VREF voltage. Those devices with differential
inputs have a nominal full scale range equal to twice the applied
VREF voltage. Each input swings VREF volts (peak-to-peak), 180°
out of phase from one another for a total differential input of
2*VREF (refer to Figures 23 and 24). Differential signaling offers several benefits over a single-ended
input, such as:
Doubling of the full-scale input range (and therefore the
dynamic range)
Improved even order harmonic distortion
Better noise immunity due to common mode rejection
Figure
24 shows the relationship between the reference voltage
and the full-scale differential input range for two different values
of VREF. Note that the common-mode input voltage must be
maintained within ±200mV of VREF/2 for differential inputs.
Those devices with singled-ended inputs have a ground-referenced
peak-to-peak input voltage span equal to the reference voltage.
FIGURE 21. IDEAL TRANSFER CHARACTERISTICS, DIFFERENTIAL INPUT
FIGURE 22. IDEAL TRANSFER CHARACTERISTICS, SINGLE-ENDED INPUT
1LSB = 2VREF/4096
100...000
100...001
100...010
111...111
000...000
000...001
011...110
011...111
AD
C
O
DE
ANALOG INPUT
AIN+ – (AIN–)
–V
REF
+ LSB
+VREF
– 1LSB
0V
+VREF
– 1LSB
1LSB = VREF/4096
000...000
000...001
000...010
011...111
100...000
100...001
111...110
111...111
AD
C
O
DE
ANALOG INPUT
0 = + LSB
FS = +VREF-1LSB
FIGURE 23. DIFFERENTIAL INPUT SIGNALING
ISL2631X/32X
VCM
VREF (P-P)
AIN+
AIN-
FIGURE 24. RELATIONSHIP BETWEEN VREF AND FULL-SCALE
RANGE FOR DIFFERENTIAL INPUTS
3.0
5.0
2.0
1.0
4.0
AIN+
AIN–
2.5Vp-p
VREF = 2.5V
3.0
5.0
2.0
1.0
4.0
AIN+
AIN–
VCM
5Vp-p
VREF = 5V
t
V
t
V
ALLOWABLE VCM RANGE