ML2281, ML2282, ML2284, ML2288
ZERO ERROR ADJUSTMENT
(where the LSB is calculated for the desired analog span,
1 LSB = analog span/256) is applied to selected “+” input
and the zero reference voltage at the corresponding “–”
input should then be adjusted to just obtain the 00000000
to 00000001 code transition.
The zero of the A/D does not require adjustment. If the
minimum analog input voltage value, V
is not ground,
IN MIN
a zero offset can be done. The converter can be made to
output 00000000 digital code for this minimum input
voltage by biasing any V – input at this V
value.
IN
IN MIN
The full-scale adjustment should be made by forcing a
This utilizes the differential mode operation of the A/D.
voltage to the V + input which is given be:
IN
The zero error of the A/D converter relates to the location
of the first riser of the transfer function and can be
(V
− V
256
)
MAX
MIN
V
IN
+ fs adjust = V
−1.5×
MAX
measured by grounding the V – input and applying a
IN
small magnitude positive voltage to the V + input. Zero
IN
error is the difference between the actual DC input
voltage which is necessary to just cause an output digital
code transition from 00000000 to 00000001 and the ideal
where
The V
V
V
REF
= high end of the analog input range
MAX
MIN
= low end (offset zero) of the analog range
1/2 LSB value (1/2 LSB = 9.8mV for V
= 5.000V ).
REF
DC
or V voltage is then adjusted to provide a
CC
code change from 11111110 to 11111111.
FULL-SCALE ADJUSTMENT
The full-scale adjustment can be made by applying a
differential input voltage which is 1-1/2 LSB down from
the desired analog full-scale voltage range and then
SHUNT REGULATOR
A unique feature of ML2288 and ML2284 is the inclusion
of a shunt regulator connected from V+ terminal to
ground which also connects to the V terminal (which is
the actual converter supply) through a silicon diode as
shown in Figure 8. When the regulator is turned on, the
V+ voltage is clamped at 11V set by the internal resistor
adjusting the magnitude of the V
input or V for a
REF
CC
CC
digital output code which is just changing from 11111110
to 11111111.
BE
ADJUSTMENT FOR AN ARBITRARY ANALOG
INPUT VOLTAGE RANGE
ratio. The typical I-V of the shunt regulator is shown in
Figure 9. It should be noted that before V+ voltage is high
enough to turn on the shunt regulator (which occurs at
about 5.5V), 35kW resistance is observed between V+ and
GND. When the shunt regulator is not used, V+ pin
should be either left floating or tied to GND. The
If the analog zero voltage of the A/D is shifted away from
ground (for example, to accommodate an analog input
signal which does not go to ground), this new zero
reference should be properly adjusted first. A V + voltage
IN
temperature coefficient of the regulator is –22mV/°C.
which equals this desired zero reference plus 1/2 LSB
V
I+
12V
V+
CC
I + →
15mA
28.8k
CURRENT LIMITING
RESISTOR, I+ ≤15mA
3.2k
3.2k
1
35k
GND
SLOPE =
V+
5.5V 6.9V
Figure 8. Shunt Regulator
Figure 9. I-V Characteristic of the Shunt Regulator
15
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
