Applications information – Rainbow Electronics MAX5489 User Manual
Page 10
MAX5487/MAX5488/MAX5489
Dual, 256-Tap, Nonvolatile, SPI-Interface,
Linear-Taper Digital Potentiometers
10
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This command may affect one potentiometer at a time,
or both simultaneously, depending on the state of A1
and A0. Alternatively, the “write NV register” command
can be used to store the current position of the wiper to
the NV register.
Copy NV Register to Wiper Register (Command 11)
This command (C1, C0 = 11) restores the wiper position
to the previously stored position in the NV register. This
command may affect one potentiometer at a time, or both
simultaneously, depending on the state of A1 and A0.
Nonvolatile Memory
The internal EEPROM consists of a nonvolatile register
that retains the last stored value prior to power-down.
The nonvolatile register is programmed to midscale at
the factory. The nonvolatile memory is guaranteed for
200,000 wiper write cycles and 50 years for wiper data
retention.
Power-Up
Upon power-up, the MAX5487/MAX5488/MAX5489
load the data stored in the nonvolatile wiper register
into the volatile memory register, updating the wiper
position with the data stored in the nonvolatile wiper
register. This initialization period takes 5µs.
Standby
The MAX5487/MAX5488/MAX5489 feature a low-power
standby mode. When the device is not being pro-
grammed, it enters into standby mode and supply cur-
rent drops to 0.5µA (typ).
Applications Information
The MAX5487/MAX5488/MAX5489 are ideal for circuits
requiring digitally controlled adjustable resistance,
such as LCD contrast control (where voltage biasing
adjusts the display contrast), or for programmable fil-
ters with adjustable gain and/or cutoff frequency.
Positive LCD Bias Control
Figures 4 and 5 show an application where the
MAX5487/MAX5488/MAX5489 provide an adjustable,
positive LCD-bias voltage. The op amp provides buffer-
ing and gain to the resistor-divider network made by
the potentiometer (Figure 4) or by a fixed resistor and a
variable resistor (Figure 5).
Programmable Filter
Figure 6 shows the MAX5487/MAX5488/MAX5489 in a
1st-order programmable-filter application. Adjust the gain
of the filter with R
2
, and set the cutoff frequency with R
3
.
Figure 3. Digital-Interface Format
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
SCLK
C1
C0
D7
D6
D5
D4
D3
D2
D1
D0
A1
A0
8
7
6
5
4
3
2
1
C1
C0
A1
A0
DIN
SCLK
CS
B) 8-BIT COMMAND WORD
A) 16-BIT COMMAND/DATA WORD
CS
DIN