Datasheet

DS3906
Triple NV Low Step Size Variable
Resistor Plus Memory
8 _____________________________________________________________________
ADDRESS TYPE NAME FUNCTION
FACTORY
DEFAULT
00h to 0Fh EEPROM
User memory
16 bytes of general-purpose user EEPROM. 00h
F8h EEPROM Resistor 0 3Fh
F9h EEPROM Resistor 1 3Fh
FAh EEPROM Resistor 2
Resistor 0-2 settings. See Table 2 and the Resistor
Registers/Settings section.
3Fh
FBh-FFh Reserved
Table 1. DS3906 Memory Map
ADDRESS VARIABLE RESISTOR
POSITION 3FH RESISTANCE
(kΩ)
NUMBER OF POSITIONS*
F8h Resistor 0 2.54
F9h Resistor 1 2.54
FAh Resistor 2 1.45
64 (00h to 3Fh) + High-Z
Table 2. DS3906 Resistor Registers
* Writing a value greater than 3Fh to any of the resistor registers makes the corresponding resistor go High-Z. Position 3Fh is the
maximum position.
makes the corresponding resistor go High-Z. Plots for
both resistor sizes are shown on the front page of this
data sheet. It can be seen that, when an external resis-
tor is connected in parallel with the DS3906’s resistors,
the effective resistance is linear and capable of achiev-
ing sub-ohm and ohm steps.
The resistor settings are stored in EEPROM memory. It
is important to point out that the DS3906 EEPROM is
organized in 2-byte pages. This is transparent when
reading from the device or when performing single byte
writes. However, this limits the maximum number of
bytes that can be written in one I
2
C transaction to two.
Furthermore, the multiple byte writes must begin on
even memory addresses (00h, 02h, …., F8h, etc).
Additional information is provided later in the I
2
C
Communication section . Example communication
transactions are provided in Figure 3.