mc44251 Freescale Semiconductor, Inc, mc44251 Datasheet - Page 10

• Manufacturer Part Number: mc44251
• Description: Triple 8-bit Video Three-state Outputs
• Manufacturer: Freescale Semiconductor, Inc

RESTRICTIONS ON V DD(R)
as V DD(R) = V DD(A) = V DD(D) and the safe operating
range of V DD(R) is defined as 0
where V DD(R) is operated at values other than V DD , it should
be noted that the accuracy of the conversion process is re-
duced. In all cases V DD(R) should not be allowed to exceed
V DD .
defined as SSI. We may define an error component, , as the
difference between the actual step size and the ideal step
size so that
where w is the greatest value of . The origin of this error is
the offset mismatch from one comparator to another and is
nearly independent of V DD(R) and V DD .
main constant for all values of V DD(R) .
MC44251
10
The normal operating condition for the MC44251 is defined
The step size is defined as SS(n) and the ideal step size is
We may also define a worst case value for
Since
The step size error, SSE, is defined as
Furthermore, the ideal step size SSI is defined as
Transition Voltage: Voltage at which transition from step
Step Size: Difference between two consecutive transition
n to step n+1 occurs = V T (n).
voltages.
is nearly independent of V DD(R) , its value will re-
SSE(n) = (SSI – SS(n))/SSI = (n)/SSI.
SS(n)
SSI = V DD(R)
+
= |SSI – SS(n)|.
V
T
OUTPUT
(n)
CODE
n+4
n+3
n+2
n+1
*
w
n
0.6/255.
V
V DD(R
T
(n
*
)
1)
V DD . In cases
as
V T (n) V T (n+1) V T (n+2)
DEFINITIONS
Figure 9.
step size error, SSE, will increase as V DD(R) is decreased.
Further study will show that the differential nonlinearity, DNL,
will also increase as V DD(R) is reduced. To minimize these
errors it is desirable to keep V DD(R) as high as possible.
Since the maximum value for V DD(R) is V DD ,
is the value that produces the greatest conversion accuracy.
INPUT VOLTAGE RANGE
the MC44251, the following restrictions apply:
on the dither generator).
ing on the dither generator).
rect value of the input voltage.
voltage range for V in without saturation is
saturation of about 3 V for V DD = 5 V.
Since is a constant and SSI is proportional to V DD(R) , the
In applications where the input signals are dc coupled to
If V in V min , then the output code = $00 or $01 (depending
If V in V max , then the output code = $FE or $FF (depend-
If V min V in V max , then the output code reflects the cor-
If the input is video based and ac coupled, then the input
For V in this reflects a maximum video input level before
Mid–Point Voltage:
V
M
V M (n+3)
(max code)
V T (n+3)
V DD(R) = V DD(D) = V DD(A)
V
M
+
(n)
0
V
+
DD(R)
V in
V
T
(n)
V in
)
V range .
)
V
V
2
T
T
(max code
2
(n
*
1)
MOTOROLA
*
1)