DS3904 Maxim Integrated Products, DS3904 Datasheet - Page 7

• Manufacturer Part Number: DS3904
• Description: DS3904, DS3905 Triple, 128-Position, Nonvolatile, Variable, Digital Resistor/switch
• Manufacturer: Maxim Integrated Products

The DS3904/DS3905 contain three, 128-position, NV,
low temperature coefficient, variable digital resistors.
They are controlled through a 2-wire serial interface,
and can serve as a low-cost replacement for designs
using conventional trimming resistors. Furthermore, the
DS3904 address pin (A0) allows two DS3904s to be
placed on the same 2-wire bus. The three address pins
on the DS3905 allow up to eight DS3905s to be placed
on the same 2-wire bus.
With their low cost and small size, the DS3904/DS3905
are well tailored to replace larger mechanical trimming
variable resistors. This allows the automation of calibra-
tion in many instances because the 2-wire interface can
easily be adjusted by test/production equipment.
The variable resistors of the DS3904/DS3905 are
addressed by communicating with the registers in
Table 1.
By taking advantage of the high-impedance mode, a
switch can be created to produce a digital output.
Setting a resistor register to 00h creates the low state.
Writing 80h into the same resistor register enables the
high-impedance state. When used with an external
pullup resistor, such as a 4.7k
is generated.
NAME
GND
SDA
SCL
V
H2
H1
H0
A0
A1
A2
CC
Variable Resistor Memory Organization
DS3904
—
—
1
2
3
4
5
6
7
8
PIN
Using the Resistor as a Switch
DS3905
10
2
3
4
5
6
7
8
9
1
Detailed Description
Triple 128-Position Nonvolatile Digital
2-Wire Serial Data. Open-drain
input/output for 2-wire data.
2-Wire Serial Clock. Input for
2-wire clock.
Supply Voltage Terminal
Ground Terminal
Resistor 2 High Terminals
Resistor 1 High Terminals
Resistor 0 High Terminals
Address-Select Pin
Ad d r ess- S el ect P i n ( D S 3905 Onl y)
Ad d r ess- S el ect P i n ( D S 3905 Onl y)
Pin Description
DESCRIPTION
pullup, a high state
_____________________________________________________________________
Variable Resistor/Switch
The SDA pin is normally pulled high with an external
resistor or device. Data on the SDA pin can only change
during SCL low time periods. Data changes during SCL
high periods indicate a start or stop condition depend-
ing on the conditions discussed below. See the timing
diagrams for further details (Figures 2 and 3).
A high-to-low transition of SDA with SCL high is a start
condition, which must precede any other command. See
the timing diagrams for further details (Figures 2 and 3).
A low-to-high transition of SDA with SCL high is a stop
condition. After a read or write sequence, the stop com-
mand places the DS3904/DS3905 into a low-power
mode. See the timing diagrams for further details
(Figures 2 and 3).
All address and data bytes are transmitted through a
serial protocol. The DS3904/DS3905 pull the SDA line
low during the ninth clock pulse to acknowledge that
they have received each byte.
The DS3904/DS3905 feature a low-power mode that is
automatically enabled after power-on, after a stop com-
mand, and after the completion of all internal operations.
Table 1. Variable Resistor Registers
*Writing a value greater than 7Fh to any of the resistor registers
sets the high-impedance mode control bit (RHIZ, the MSB of
the resistor register) resulting in the resistor going into high-
impedance mode. Position 0 is the minimum position. Position
127 is the maximum position.
ADDRESS
FAh
F8h
F9h
VARIABLE
RESISTOR
Resistor 0
Resistor 1
Resistor 2
Clock and Data Transitions
POSITION 7Fh
RESISTANCE
Device Operation
(nominal)
(nominal)
(nominal)
20k
20k
20k
Start Condition
Stop Condition
Standby Mode
Acknowledge
NUMBER OF
POSITIONS*
128 (00h to
7Fh) + Hi-Z
128 (00h to
7Fh) + Hi-Z
128 (00h to
7Fh) + Hi-Z
7