Rainbow Electronics MAX5419 - Manual (Page 11)

MAX5417/MAX5418/MAX5419
256-Tap, Nonvolatile, I 2 C-Interface,
Digital Potentiometers
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ADDRESS BYTE CONTROL BYTE DATA BYTE
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 STOP
SCL
CYCLE
NUMBER
START
A6 A5 A4 A3 A2 A1 A0 ACK TX NV V R3 R2 R1 R0 ACK D7 D6 D5 D4 D3 D2 D1 D0 ACK
VREG 0 1 0 1 A2 A1 A0 0 0 0 0 1 0 0 0 1 D7 D6 D5 D4 D3 D2 D1 D0
NVREG 0 1 0 1 A2 A1 A0 0 0 0 1 0 0 0 0 1 D7 D6 D5 D4 D3 D2 D1 D0
NVxVREG 0 1 0 1 A2 A1 A0 0 0 1 1 0 0 0 0 1 D7 D6 D5 D4 D3 D2 D1 D0
VxNVREG 0 1 0 1 A2 A1 A0 0 0 1 0 1 0 0 0 1 D7 D6 D5 D4 D3 D2 D1 D0
Table 2. Command Byte Summary
Nonvolatile Memory
The internal EEPROM consists of an 8-bit nonvolatile
register that retains the value written to it before the
device is powered down. The nonvolatile register is
programmed with the zero-scale value at the factory.
Power-Up
Upon power-up, the MAX5417/MAX5418/MAX5419
load the data stored in the nonvolatile memory register
into the volatile memory register, updating the wiper
position with the data stored in the nonvolatile memory
register. This initialization period takes 10µs.
Standby
The MAX5417/MAX5418/MAX5419 feature a low-power
standby. When the device is not being programmed, it
goes into standby mode and power consumption is
typically 500nA.
Applications Information
The MAX5417/MAX5418/MAX5419 are intended for cir-
cuits requiring digitally controlled adjustable resis-
tance, such as LCD contrast control (where voltage
biasing adjusts the display contrast), or for programma-
ble filters with adjustable gain and/or cutoff frequency.
Positive LCD Bias Control
Figures 9 and 10 show an application where the volt-
age-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 9) or to a fixed
resistor and a variable resistor (see Figure 10).
Programmable Filter
Figure 11 shows the configuration for 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
V OUT
30V
5V
W
H
L
MAX5417
MAX5418
MAX5419
V OUT
30V
5V
W
H
L
MAX5417
MAX5418
MAX5419
Figure 9. Positive LCD Bias Control Using a Voltage-Divider Figure 10. Positive LCD Bias Control Using a Variable Resistor