isl24201 Intersil Corporation, isl24201 Datasheet - Page 7

• Manufacturer Part Number: isl24201
• Description: Programmable Vcom Calibrator With Eeprom
• Manufacturer: Intersil Corporation

The maximum voltage on the SET pin is A
the minimum voltage difference between the V
calculate the minimum V
Output Voltage
The output voltage, V
Equation 6:
While Equation 6 can be used to calculate the output voltage, it
does not help select the values of R
specific range of V
Output Voltage Span Calculation
The span of the output voltage is typically centered around the
nominal V
A
value of zero, while the low V
value of 255. Figure 7 shows the definition of several terms used
later in the text.
There are three variables that control the V
operating point; the span of the V
current sink and the source impedance of the resistive divider.
Figure 8 shows a range of operating points for these three variables
and a quick way to estimate a specific operating point. The X-axis is
the span of the V
Voltage), and the Y-axis is the maximum sink current set by R
The individual plots of each R
the maximum OUT sink current given that value of source
impedance of the voltage divider. R
resistance of the voltage divider R
of the parallel combination of R
The span of the V
R
V
V
V
VDD
COM
OUT
TH
OUT
=
(
SPAN
voltage. The high V
=
MIN
------------------- -
R
R
A
1
1
VDD
+
COM
)
G N D
R
A
≥
R
=
2
VDD
A
------------- -
2
⎛
⎜
⎝
FIGURE 7. VOLTAGE LEVELS FOR V
I
VDD
20
------------------- -
R
voltage value, which is typically near half of the
SET
COM
1
R
COM
+
2
(
COM
+
R
N O M IN AL V
R
2
MinimumSaturationVoltage
TH
voltage (High V
OUT
⎞
⎟
⎠
H IG H V
LO W V
voltage is shown by Equation 8.
⎛
⎜
⎝
)
voltages.
1
OUT
, of the OUT pin can be calculated from
COM
–
RegisterValue
-------------------------------------------------- -
TH
voltage, as shown in Equation 5.
COM
voltage occurs with the register
CO M
CO M
1
show the V
7
CO M
and R
1
voltage occurs with the register
V O LTA G E
COM
TH
V O LTAG E
256
and R
COM
1
VO LTAG E
is the Thevenin equivalent
, R
2
voltage, the maximum
, as shown in Equation 7.
2
VDD
Voltage - Low V
2
COM
, which is the resistance
and R
+
COM
/20 and is added to
1
OUT
⎛
⎜
⎝
span plotted against
------------------- -
20R
COM
SET
calibrator’s
R
and SET pins to
1
SET
SPAN
to obtain a
⎞
⎟
⎠
COM
⎞
⎟
⎠
ISL24201
SET
(EQ. 6)
(EQ. 8)
(EQ. 5)
(EQ. 7)
.
To make a final selection of the resistor values for R
supply voltage A
calculations for R
R
The R
voltage being centered at half the A
As an example, A
selected to be 100µA and the required span is 2V. Using Figure 8
as a guide, the V
minimum is equal to 6.5V. Rearranging equation and calculation
the value of R
Calculating the value of R
Calculating the value of R
R
R
R
R
1
SET
1
2
2
FIGURE 8. GRAPH of V
=
=
=
=
1
40R
----------------------------------------- -
=
40 7500
---------------------------------- -
40 7500
---------------------------------- -
0.6
0.5
0.4
0.3
0.2
0.1
40R
----------------------------------------- -
A
A
and R
VDD
------------------------------------ -
20I
0
VDD
(
(
15
15 2
0
SET
SET
OUT
A
+
+
–
–
(
2
VDD
(
SPAN
SET
2
AND R
SPAN
SPAN
SPAN
) 2 ( )
) 2 ( )
(
calculations are based on the span of the V
MAX
VDD
COM
:
VDD
1
1
and R
=
=
)
TH
)
)
and the value of R
maximum is equal to 8.5V and the V
39.29kΩ
46.15kΩ
= 15V, the maximum value for I
=
------------------------------------- -
20 0.000100
COM
2
1
2
2
are shown in Equations 9 and 10:
(
is shown in Equation 12.
V
is shown in Equation 13.
COM
SPAN vs MAXIMUM OUTCURRENT
15
3
SPAN (V)
VDD
)
=
SET
voltage.
7500Ω
4
are specified. The
5
December 9, 2010
1
and R
SET
FN7586.1
is
(EQ. 11)
(EQ. 12)
(EQ. 13)
(EQ. 10)
COM
COM
6
2
(EQ. 9)
, The