isl24212 Intersil Corporation, isl24212 Datasheet - Page 7

• Manufacturer Part Number: isl24212
• Description: Programmable Vcom Calibrator With Eeprom And Output Buffer
• Manufacturer: Intersil Corporation

The maximum value of I
substituting the maximum register value of 255 into Equation 2,
resulting in Equation 3:
DVROUT
Equation 2 can also be used to calculate the unit sink current
step size per Register Code, resulting in Equation 4:
Determination of R
The ultimate goal for the ISL24212 is to generate an adjustable
voltage between two endpoints, V
a fixed power supply voltage, AV
choosing the correct values for R
of R
work under most conditions. Equation 5 calculates the minimum
R
Note that this is the absolute minimum value for R
R
proportional to R
Determination of R
With AV
per the above requirements, R
Equations 6 and 7:
Final Transfer Function
The voltage at the DVR_OUT pin can be calculated from
Equation 8:
With amplifier A2 in the unity-gain configuration (V
to IN
Example
As an example, suppose the A
V
arbitrarily chosen to be 7.5k
I
R
R
R
V
STEP
COM_MIN
SET
SET
SET
DVROUT
1
2
=
=
SET
N
(
value:
values reduce quiescent power, since R
MIN
5120 R
5120 R
=
as shown in Figure 5), V
(
DD
is not critical. Values from 1k to more than 100k will
MAX
--------------------------------------------- -
(
256
)
=
= 6.5V and the desired V
, V
=
⋅
⋅
AV
)
COM(MIN)
) 20
⎛
⎜
⎜
⎜
⎜
⎝
AV
(
SET
SET
=
----------------------------------------------------- -
⎛
⎝
DD
V
DD
------------------- -
20R
OUT MIN
SET
⎛
⎜
⎝
⎛
⎜
⎝
⎛
⎜
⎝
) R
A
(
-------------------------------------------------------------------------------- -
256 V
-------------------------------------------------------------------------------------------------------------------- -
255 AV
------------------- -
R
VDD
. The ISL24212 is tested with a 5k
1
(
SET
SET
R
V
+
AV
--------------
COM MAX
2
and V
⋅
⋅
16
R
)
DVR_OUT
DD
2
)
COM MAX
⎞
⎟
⎠
–
DD
(
⎛
⎜
⎝
V
SET
AV
--------------
1
1
Ω
COM(MAX)
COM MAX
20
(
+
–
.
and R
DD
VDD
1
DVROUT
)
V
RegisterValue
-------------------------------------------------- -
7
DD
and R
–
COM MIN
⎞
⎠
(
SET
can be calculated by
COM_MIN
⎞
⎟
⎟
⎟
⎟
⎠
)
V
supply is 15V, the desired
COM_MAX
. This is accomplished by
(
–
COM MIN
kΩ
, R
(
V
)
COM MIN
2
2
256
–
= V
known and R
1
)
(
can be determined using
V
and R
)
COM MIN
COM_OUT
(
–
and V
)
256 V
1
= 8.5V. R
(
)
+
2
and R
⎞
⎟
⎠
⋅
1
. The exact value
COM_MAX
⎛
⎜
⎝
)
COM MAX
------------------- -
20R
SET
COM_OUT
= V
SET
R
2
. Larger
(
1
SET
SET
are
Ω
COM
chosen
R
⎞
⎟
⎠
is
SET
ISL24212
, with
⎞
⎟
⎠
)
(EQ. 8)
.
(EQ. 3)
(EQ. 4)
(EQ. 5)
(EQ. 7)
(EQ. 6)
⎞
⎟
⎠
tied
.
First, verify that our chosen R
requirement described in Equation 5:
Using Equations 6 and 7, calculate the values of R
Table 1 shows the resulting V
value for these conditions.
Output Voltage Span Calculation
It is also possible to calculate V
existing resistor values.
V
from the middle node of the R1/R2 divider. Substituting
RegisterValue = 255 into Equation 8 gives the following:
Similarly, RegisterValue = 0 for V
(
R
R
V
V
7.5kΩ
COM_MIN
COM MAX
1
2
COM MIN
=
=
(
(
5120 7500
5120 7500
)
>
REGISTER VALUE
TABLE 1. EXAMPLE V
⎛
⎜
⎜
⎜
⎝
)
)
occurs when the greatest current, I
R
⋅
⋅
=
=
SET
AV
AV
100
120
127
140
160
180
200
220
240
255
(
20
40
60
80
MIN
0
DD
DD
⋅
⋅
⎛
⎝
⎛
⎝
⎛
⎜
⎝
⎛
⎜
⎝
------------------------------------- -
256 8.5
----------------------------------------------------------------- -
255 15
------------------- -
------------------- -
)
R
R
=
1
1
R
R
8.5 6.5
+
+
⎛
⎜
⎜
⎜
⎝
⋅
⋅
2
2
R
------------------------------
⎛
⎝
R
6.5V
–
2
2
8.5 6.5
⎞
⎟
⎠
⎞
⎟
⎠
+
–
COM
⎛
⎜
⎝
⎛
⎜
⎝
15
------ -
16
SET
DVR_OUT
1
6.5 256 8.5
1
6.5
–
COM(MIN)
–
–
–
15
------ -
20
COM(MAX)
⎛
⎜
⎝
⎞
⎠
--------- -
256
meets the minimum
–
voltage as a function of register
------------------- -
20R
1
⎞
⎠
=
⎞
⎟
⎟
⎟
⎠
R
⎛
⎜
⎝
=
35.4kΩ
vs REGISTER VALUE
1
SET
------------------- -
20R
⋅
0.163kΩ
and V
R
⎞
⎟
⎠
1
SET
⎞
⎟
⎠
:
⎞
⎠
V
=
DVR_OUT
⎞
⎟
⎠
DVR(MAX),
COM(MAX)
⎞
⎟
⎠
46.4kΩ
⎞
⎟
⎟
⎟
⎠
8.18
8.49
8.34
8.02
7.87
7.71
7.55
7.50
7.40
7.24
7.09
6.93
6.77
6.62
6.50
1
and R
March 15, 2011
(V)
is drawn
from the
(EQ. 12)
FN7590.0
(EQ. 10)
(EQ. 11)
(EQ. 13)
2
(EQ. 9)
: