Rainbow Electronics DS2890 User Manual

DS2890

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www.maxim-ic.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

§ 100 kW resistor element value

§ T0-92 package provides a 1-Wire® variable

resistor configuration

§ 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 142 kbits per
second

o

§ -40

§ 2.8V – 6.0V operating voltage range

C to +85oC operating temperature range

1-Wire Di

ital Potentiomete

PIN ASSIGNMENT

Top View

6-pin TSOC

6

GND

1-WIRE

VDD

123

side view

Visit www.dalsemi.com for Flip Chip pinout and
mechanical data.

1
2

3

TO-92 Package

Bottom View

RH

GND

1-WIRE

Flip Chip Package

RL

5

WIPER

4

RH

123

top view

ORDERING INFORMATION

PART NUMBER RESISTANCE

DS2890-000

DS2890P-000

DS2890X-000

DS2890-000/T&R

DS2890P-000/T&R

100 kW

100 kW

100 kW

100 kW

100 kW

* Contact the factory for availability of alternate resistance values

1-Wire is a registered trademark of Dallas Semiconductor.

*

PACKAGE DESCRIPTION

T0-92

6-pin TSOC

Flip Chip Pkg., Tape & Reel

Tape & Reel of DS2890

Tape & Reel of DS2890P

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PIN DESCRIPTION

SIGNAL
NAME TYPE FUNCTION

1-WIRE I/O 1-Wire bus interface. Open drain, requires external pull-up resistor. Range:

2.8V – 6.0V. See HARDWARE CONFIGURATION for pull-up resistor
recommendations.

DS2890

RH

I/O 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.

RL

I/O Low end terminal of potentiometer resistor element. Range: 0V – 11.0V.

Range independent of 1-Wire or V

supply levels as well as the voltage

DD

levels applied to the other potentiometer terminals.

WIPER

I/O 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.

V

DD

GND

PWR Auxiliary power supply input. Range: 2.8V – 6.0V

PWR Ground

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 0–11 volt 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: a) 1-Wire only mode in which device power is supplied parasitically
from the 1-Wire and b) VDD mode where power is supplied from an external supply With a VDD supply
the device can support both a potentiometer and variable resistor configuration. When operating in a 1­Wire only power mode the device supports only a variable resistor configuration.

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DS2890

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 V

supply is applied within operating limits.

DD

Otherwise, a power-on reset will occur and the wiper position and operating state will return to power-on
default conditions.

FIGURE 1. DS2890 BLOCK DIAGRAM

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.

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FIGURE 2. 1-Wire Command Hierarchical Structure

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”).

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DS2890

FIGURE 3. 1-WIRE POTENTIOMETER FEATURE REGISTER

Feature Register Bit Encoding

b7 b6 b5 b4 b3 b2 b1 b0

PR NWP NP WSV PC

Feature Register Bit Definitions

Feature Description Bit(s) Definition

If 0: logarithmic potentiometer element(s)

PC: potentiometer characteristic b0

If 1: linear potentiometer element(s)

If 0: wiper setting(s) are non-volatile

WSV: wiper setting volatility b1

If 1: wiper setting(s) are volatile

NP: number of potentiometers b3..b2 2 bit binary value representing number of potentiometers:

If 00b: 1 potentiometer

If 01b: 2 potentiometers

If 10b: 3 potentiometers

If 11b: 4 potentiometers

NWP: number of wiper positions b5..b4

PR: potentiometer resistance b7..b6 2 bit binary value representing potentiometer resistance:

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”.

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

If 00b: 5 kW

If 01b: 10 kW

If 10b: 50 kW

If 11b: 100 kW

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.

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FIGURE 4. POTENTIOMETER CONTROL REGISTER

Control Register Bit Encoding

b7 b6 b5 b4 b3 b2 b1 b0

DS2890

XCPC X X

Control Register Bit Definitions*

Description Bit(s) Definition

WN: wiper number to control b1..b0

WN

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

WN : inverted wiper number to

b3..b2

1’s complement of potentiometer wiper to control:

control

If 11b: potentiometer 1 wiper

If 10b: potentiometer 2 wiper

If 01b: potentiometer 3 wiper

If 00b: potentiometer 4 wiper

WN

If 0: the charge pump is OFF

CPC: charge pump control b6

If 1: the charge pump is ON

These bits are reserved for future use by Dallas

X: don’t care. b4,b5,b7

Semiconductor. These bits should be written to a value of

0.

*Note:

Control Register power-on defaults: Charge Pump is OFF (CPC=0), Wiper Number to control is wiper #1

(WN=00b,

Valid DS2890 control values are highlighted:
Thus for the DS2890, valid control register values are:

Control Register Value Description

As shown in Figure 22 and discussed in the “POTENTIOMETER FUNCTION COMMANDS” section,
no change in device state will occur if an invalid control register value is sent.

WN =11b).

value

00001100b charge pump off, potentiometer #1 wiper selected
01001100b charge pump on, potentiometer #1 wiper selected

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DS2890

POWER and CONFIGURATION CONSIDERATIONS

1-Wire devices can typically derive operating power entirely from the 1-Wire bus by storing energy on an
internal capacitor during periods of time when the 1-Wire bus is in a high state. During bus low times the
device continues to operate from the energy stored on the internal capacitor; the capacitor is then
recharged when the bus returns to a high state. This technique of operating entirely from the 1-Wire bus
by powering from energy stored on an internal capacitor during bus low times in known as “parasite
powered” operation. Special consideration is required with the DS2890 in that it supports two power
configurations and two related digital resistor modes: Potentiometer Configuration and Variable Resistor
Configuration. The Potentiometer Configuration requires the presence of a VDD power source to supply
the power needs of the device charge pump which must be turned on to support a terminal-to-terminal
wiper output range. The Variable Resistor configuration is supported with or without a VDD source or
enabled charge pump although resistance range, as described below, is influenced by the charge pump
state.

POTENTIOMETER CONFIGURATION

To configure and operate the DS2890 as a potentiometer as shown in Figure 5 requires the TSOC or flip
chip package, a VDD power source, and the device charge pump turned on (Control Register, bit
CPC=1). The charge pump must be enabled to support RL to RH terminal voltage swings at the WIPER
output and as described previously, a VDD supply must be provided to support the power requirements
of the charge pump.

Figure 5. Potentiometer Configuration

RH

WIPER

RL

2.8V to 6.0V

Bus

Master

2.8V to 6.0V

VDD

1-WIRE

GND

VARIABLE RESISTOR CONFIGURATION

The Variable Resistor configuration as shown in Figure 6 is supported by all package types with or
without an external VDD supply. As described previously, without a VDD source the charge pump must
be disabled.

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DS2890

Figure 6. Variable Resistor Configurations

2.8V to 6.0V

2.8V to 6.0V

Bus

Master

or

No Connect

VDD

1-WIRE

GND

RH

WIPER

RL

2.8V to 6.0V

Bus

Master

1-WIRE

GND

(TO92 Package)

RH

WIPER RESISTANCECONSIDERATIONS

A simplified diagram of the DS2890 resistor array for the potentiometer configuration is shown in
FIGURE 8. In this figure the

resistance R

. The value of R

WIPER

terminal voltage. Wiper resistance is significantly reduced when an external VDD supply is used and the
device charge pump is enabled. A wiper resistance graph with the charge pump enabled is shown in
FIGURE 10.

r

resistance of the wiper transistors in Figure 1 are modeled as wiper

DS

varies with device configuration, operational state, and wiper

WIPER

FIGURE 8. Potentiometer Resistor Model

R

WIPER

RH

WIPER

RL

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DS2890

FIGURE 10. Typical Wiper Resistance vs Wiper Voltage at 25oC,

Charge Pump ON

1000

Wiper Resistance (ohms)

100

0.1 5.5 11

Voltage Across Wiper (V)

When packaged in a 3-pin TO-92 or configured as a variable resistor, the DS2890 takes on a
configuration as shown in FIGURE 11, a simplified model is shown in Figure 12. As shown, the RL and
Wiper terminals and are connected to GND and the resistance between the RH terminal and GND is
varied. As described previously, the DS2890 charge pump must be turned off (default state) for operation
with the TO-92 package or when VDD is not applied. Wiper resistance for a configuration with the
charge pump disabled is shown in FIGURE 13.

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