Applications information, Standby mode, Positive lcd bias control – Rainbow Electronics MAX5475 User Manual
Page 8: Programmable filter, Truth table
MAX5471/MAX5472/MAX5474/MAX5475
32-Tap, Nonvolatile, Linear-Taper Digital
Potentiometers in SOT23
8
_______________________________________________________________________________________
Standby Mode
The MAX5471/MAX5472/MAX5474/MAX5475 are
always in standby mode, except during the transition of
a logic input or while the wiper position is being stored.
When in standby mode, the static supply current is
reduced to less than 1µA and the resistive terminals (H,
W, and L) are unaffected.
Applications Information
The MAX5471/MAX5472/MAX5474/MAX5475 are
intended for circuits requiring digitally controlled
adjustable resistance, such as LCD contrast control
(where voltage biasing adjusts the display contrast), or
programmable filters with adjustable gain and/or cutoff
frequency.
Positive LCD Bias Control
Figures 4 and 5 show an application where the voltage-
divider or variable resistor is used to make an
adjustable, positive LCD-bias voltage. The op amp pro-
vides buffering and gain to the resistor-divider network
made by the potentiometer (Figure 4) or to a fixed
resistor and a variable resistor (Figure 5).
Programmable Filter
Figure 6 shows the configuration of a 1st-order pro-
grammable filter. The gain of the filter is adjusted by
R2, and the cutoff frequency is adjusted by R3. Use the
following equations to calculate the gain (G) and the
3dB cutoff frequency (f
C
):
G
R
R
f
R
C
C
= +
=
Ч
Ч
1
1
2
1
2
3
π
CS
U/D
INC
W
L
L
↓
Decrement
L
H
↓
Increment
L
X
↑
No change
H
X
X
No change
↓
X
X
No change
↑
X
L
Position not stored
↑
X
H
Position stored
Truth Table
↓ = High-to-low transition.
↑ = Low-to-high transition.
X = Don’t care.
32-POSITION
DECODER
UP/DOWN
COUNTER
NONVOLATILE
MEMORY
V
DD
GND
INC
H
5
2
6
3
4
R
W
CS
1
S
32
S
31
S
30
S
3
S
2
S
1
MAX5471
MAX5472
U/D
R
31
R
30
R
2
R
1
Figure 2. MAX5471/MAX5472 Functional Diagram
32-POSITION
DECODER
UP/DOWN
COUNTER
NONVOLATILE
MEMORY
V
DD
GND
H
6
3
2
4
5
R
W
1
S
32
S
31
S
30
S
3
S
2
S
1
MAX5474
MAX5475
U/D
R
31
R
30
R
2
R
1
CS
INC
7
W
8
L
Figure 3. MAX5474/MAX5475 Functional Diagram