MAX5461 MAXIM [Maxim Integrated Products], MAX5461 Datasheet - Page 6

• Manufacturer Part Number: MAX5461
• Manufacturer: MAXIM [Maxim Integrated Products]

32-Tap FleaPoT
Potentiometers
All parts in this family feature power-on reset (POR) cir-
cuitry that sets the wiper position to midscale at power-
up. By default, the chip is in the increment mode.
The MAX5460–MAX5468 are intended for circuits
requiring digitally controlled adjustable resistance,
such as LCD contrast control, where voltage biasing
adjusts the display contrast.
Figure 3 shows an application where the variable resis-
tor is used with a MAX1771 to make an adjustable posi-
tive LCD-bias circuit. The output of the MAX1771 is a
positive voltage that is digitally controlled through the
MAX5461/MAX5464/MAX5467. Similarly, Figure 4
shows the application of the variable resistor in a digi-
tally controlled negative LCD-bias circuit along with the
MAX774/MAX775/MAX776.
Figure 3. Adjustable Positive LCD Bias
6
0.1µF
V
_______________________________________________________________________________________
V
68µF
IN
REF
C3
C1
= 5V
= 1.5V
5
4
6
REF
SHDN
AGND
C2
0.1µF
Applications Information
MAX1771
GND
V+
2
7
Controlling a Switch-Mode
MAX5461
MAX5464
MAX5467
EXT
CS
FB
1
8
3
V
V
22µH
OUT(MAX)
OUT(MIN)
V
V
REF
REF
L1
LCD Bias Generator
MTD20N03HDL
N
1N5817-22
R
40mΩ
R1
SENSE
=
=
Power-On Reset
R2
R1
(
D1
R1 + R
+ 1
R
™
300µF
VAR
VAR(MAX)
R2
, 2-Wire Digital
C4
C5
R2
V
)
OUT
AT 0.5A
+ 1
= 12V
Alternatively, use an op amp to provide buffering and
gain to the output of the MAX5462/MAX5465/MAX5468.
Connect the mechanical potentiometer to the positive
input of a noninverting op amp (Figure 5) to select a
portion of the input signal by digitally controlling the
wiper terminal. Figure 6 shows a similar circuit for the
MAX5461/MAX5464/MAX5467.
Figure 7 shows how to use the variable resistor to digi-
tally adjust the gain of a noninverting op amp configura-
tion. Connect the MAX5461/MAX5464/MAX5467 in
series with a resistor to ground to form the adjustable
gain control of a noninverting amplifier. The MAX5460–
MAX5468 have a low 5ppm/°C ratiometric tempco that
allows for a very stable adjustable gain configuration
over temperature.
Figure 4. Adjustable Negative LCD Bias
150µF
V
IN
C1
V
V
R1 + R
OUT(MAX)
V
REF
REF
MAX5461
MAX5464
MAX5467
- V
VAR
FB
C2
0.1µF
=
≥ 5µA (FOR 2% GAIN-SETTING ACCURACY)
R2
R1
R2
R1
,
V
OUT(MIN)
C3
0.1µF
R
V
VAR
REF
1
3
2
4
OUT
SHDN
FB
REF
=
R1 + R
MAX774
MAX775
MAX776
R2
GND
VAR
8
Alternative Positive
*
MAX775/MAX776 = 120µF, 20V
MAX774 = 330µF, 10V
EXT
LCD Bias Control
CS
V+
Adjustable Gain
5
6
7
22µH
L1
P
Q1
Si9435
R3
0.07Ω
1N5822/
MBR340
C4
*
V
OUT