DS2890.PDF

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Preliminary
DS2890
1-Wire Digital Potentiometer
www.dalsemi.com
FEATURES
Single element 256-position linear taper
potentiometer
Supports potentiometer terminal working
voltages up to 11V
Potentiometer terminal voltage independent
of supply voltage
Potentiometer wiper position controlled and
read over minimal 1-Wire bus interface
100kΩ resistor element value
Provides 1-Wire and VDD power modes
Supports Conditional Search based on
power-on default wiper position
Multiple DS2890’s can be identified on a
common 1-Wire bus and operated
independently
Unique factory lasered 64-bit registration
number assures error free device selection
and absolute part identity
Built-in multi-drop controller ensures
compatibility with other 1-Wire Network
products
Supports Overdrive mode which boosts
communication speed up to 142k bits per
second
-40
o
C to +85
o
C operating temperature range
2.8V - 6.0V operating voltage range
PIN ASSIGNMENT
6-pin TSOC
(top view)
TO-92
(bottom view)
ORDERING INFORMATION
PART NUMBER
DS2890-000
DS2890P-000
DS2890X-000
DS2890T-000
DS2890V-000
RESISTANCE
*
100kΩ
100kΩ
100kΩ
100kΩ
100kΩ
PACKAGE DESCRIPTION
T0-92
6-pin TSOC
Chip Scale Pkg., Tape & Reel
Tape & Reel of DS2890
Tape & Reel of DS2890P
* Contact the factory for availability of alternate resistance values
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DS2890
PIN DESCRIPTION
SIGNAL
NAME
1-WIRE
TYPE
I/O
FUNCTION
1-Wire bus interface. Open drain, requires external pull-up resistor. Range:
2.8V - 6.0V. See HARDWARE CONFIGURATION for pull-up resistor
recommendations.
High end terminal of potentiometer resistor element. Range: 0V - 11.0V.
Range independent of 1-Wire or VDD supply levels as well as the voltage
levels applied to the other potentiometer terminals.
Low end terminal of potentiometer resistor element. Range: 0V - 11.0V.
Range independent of 1-Wire or VDD supply levels as well as the voltage
levels applied to the other potentiometer terminals.
Potentiometer wiper terminal. Range 0V - 11.0V. Range independent of 1-
Wire or VDD supply levels as well as the voltage levels applied to the other
potentiometer terminals.
Auxiliary power supply input. Range: 2.8V - 6.0V
Ground
RH
I/O
RL
I/O
WIPER
I/O
VDD
GND
PWR
PWR
DESCRIPTION
The DS2890 is a linear taper digitally controlled potentiometer with 256 wiper positions. Device
operation, including wiper position, is controlled over the single contact 1-Wire bus for the ultimate in
electrical interface simplicity. With a wide 0V-11V working voltage range for the potentiometer
terminals, the DS2890 is ideal for a broad range of industrial and control applications. Potentiometer
terminal voltage is independent of device supply voltage as well as the voltage applied to the other
potentiometer terminals. Communication with the DS2890 follows the standard Dallas Semiconductor 1-
Wire protocol and can be accomplished with minimal hardware such as a single port pin of a
microcontroller. Multiple DS2890 devices can reside on a common 1-Wire bus and be operated
independently of each other. Each DS2890 has its own unalterable 64-bit ROM registration number that
is factory lasered into the chip. The registration number guarantees unique identification for absolute
traceability and is used to address the device in a multi-drop 1-Wire Network environment. The DS2890
will respond to a 1-Wire Conditional Search command if the potentiometer wiper is set at the power-on
default position. This feature enables the bus master to easily determine whether a potentiometer has
gone through a power-on reset and needs to be re-configured with a required wiper position setting. The
DS2890 supports two power modes: 1-Wire only mode in which device power is supplied parasitically
from the 1-Wire bus or VDD mode where power is supplied from an external supply; when operating
from VDD mode wiper resistance is reduced.
OPERATION
The DS2890 is a single element digital potentiometer; a block diagram of the device is shown in Figure 1.
The device has a total of 256 linearly spaced tap points including the RL and RH terminals; a total of 255
resistive segments exist between the RL and RH terminals. These tap points are accessible to the WIPER
terminal whose position is controlled via the 1-Wire bus interface. Wiper position and device state are
maintained as long as the 1-Wire bus is active or the VDD supply is applied within operating limits.
Otherwise, a power-on reset will occur and the wiper position and operating state will return to power-on
default conditions.
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DS2890
DS2890 BLOCK DIAGRAM
Figure 1
As shown in the figure the device has five major elements: the 1-Wire Function Controller, the
Potentiometer Controller, the 64-bit ROM, the resistor array, and Parasite Power circuitry. Each of these
elements is discussed in detail throughout the remainder of the data sheet. DS2890 control including
device selection, positioning/reading the potentiometer wiper, and device operating state is performed
over the 1-Wire bus. The hierarchical structure of the 1-Wire protocol as applicable to the DS2890 is
shown in Figure 2. As shown, the control sequence starts with the 1-Wire bus master issuing one of eight
ROM function commands. After a ROM function command is successfully completed potentiometer
functions may be executed. The protocol for ROM and potentiometer functions are described in the
“COMMAND FLOW” section. For the 3-pin TO-92 package configuration and operation see the “TO-
92 PACKAGE OPERATION” section.
1-WIRE COMMAND HIERARCHICAL STRUCTURE
Figure 2
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DS2890
DATA I/O BIT ORDER
All data is read and written least significant bit (LSB) first.
POTENTIOMETER FEATURE REGISTER
Although the feature set of the DS2890 is primarily fixed, a mechanism to identify feature characteristics
of future 1-Wire potentiometers has been developed and implemented in the DS2890. As shown in
Figure 3, the feature register is an encoded read-only byte that describes the characteristics of the DS2890
and future 1-Wire potentiometers. Feature values that correspond to the DS2890 are highlighted. The
feature register is read with the READ CONTROL REGISTER potentiometer function command (see
“POTENTIOMETER FUNCTION COMMANDS”).
1-WIRE POTENTIOMETER FEATURE REGISTER
Figure 3
Feature Register Bit Encoding
b7
b6
b5
b4
PR
NWP
Feature Register Bit Definitions
Feature Description
PC: potentiometer characteristic
WSV: wiper setting volatility
NP: number of potentiometers
b3
NP
b2
b1
WSV
b0
PC
Bit(s)
b0
b1
b3..b2
NWP: number of wiper positions
b5..b4
PR: potentiometer resistance
b7..b6
Definition
If 0: logarithmic linear potentiometer element(s)
If 1: linear potentiometer element(s)
If 0: wiper setting(s) are non-volatile
If 1: wiper setting(s) are volatile
2 bit binary value representing number of potentiometers:
If 00b:1 potentiometer
If 01b:2 potentiometers
If 10b: 3 potentiometers
If 11b: 4 potentiometers
2 bit binary value representing number of wiper positions
for each potentiometer:
If 00b:32 positions
If 01b:64 positions
If 10b: 128 positions
If 11b: 256 positions
2 bit binary value representing potentiometer resistance:
If 00b:5kΩ
If 01b:10kΩ
If 10b: 50kΩ
If 11b: 100kΩ
DS2890 feature values are highlighted:
value
The DS2890 will respond with a feature register value of F3h when a READ CONTROL
REGISTER command is executed, see section “POTENTIOMETER FUNCTION COMMANDS”.
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DS2890
POTENTIOMETER CONTROL REGISTER
The potentiometer control register is used to turn on/off the DS2890 charge pump (see section
“POTENTIOMETER WIPER RESISTANCE AND CHARGE PUMP CONSIDERATIONS” for a
discussion of the charge pump) and has control capabilities for future 1-Wire potentiometers that could
contain multiple resistor elements. The format of the control register is shown in Figure 4.
POTENTIOMETER CONTROL REGISTER
Figure 4
Control Register Bit Encoding
b7
b6
b5
b4
X
CPC
X
X
Control Register Bit Definitions*
Description
WN: wiper number to control
b3
WN
b2
b1
WN
b0
Bit(s)
b1..b0
WN : inverted wiper number to b3..b2
control
Definition
2 bit binary value representing the potentiometer wiper to
control:
If 00b:potentiometer 1 wiper
If 01b:potentiometer 2 wiper
If 10b: potentiometer 3 wiper
If 11b: potentiometer 4 wiper
1’s complement of potentiometer wiper to control:
CPC: charge pump control
X: don’t care.
If 11b:potentiometer 1 wiper
If 10b:potentiometer 2 wiper
If 01b:potentiometer 3 wiper
If 00b:potentiometer 4 wiper
If 0: the charge pump is OFF
b6
If 1: the charge pump is ON
These bits are reserved for future use by Dallas
b4,b5,b
Semiconductor. These bits should be written to a value of
7
0.
*Note: Control Register power-on defaults: Charge Pump is OFF (CPC=0), Wiper Number to
control is wiper #1 (WN=00b,
WN =11b).
Valid DS2890 control values are highlighted: value
Thus for the DS2890, valid control register values are:
Control Register Value Description
X0XX1100
charge pump off, potentiometer #1 wiper selected
X1XX1100
charge pump on, potentiometer #1 wiper selected
As shown in Figure 16 and discussed in the “POTENTIOMETER FUNCTION COMMANDS” section,
no change in device state will occur if an invalid control register value is sent.
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