Dallas Semiconductor DS1800S, DS1800E, DS1800 Datasheet

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FEATURES

 Ultra-low power consumption
 Operates from 3V or 5V supplies
 Two digitally controlled, 128-position

potentiometers including mute

 Logarithmic gain characteristics
 Zero-crossing detection eliminates noise

caused by discrete wiper changes

 Two control interfaces

- 3-wire serial CPU control

- Pushbutton control

 20-pin DIP (300-mil), 20-pin SOIV (300-

mil), and 20-pin (173-mil) TSSOP packaging
available

 Operating Temperature Range:

- Industrial: -40°C to +85°C

 Software and hardware mute
 Standard Resistance Available: 53KΩ

PIN ASSIGNMENT

PIN DESCIPTION

OUT0,OUT1 - Low-end of resistor
IN0, IN1 - High-end of resistor
W0,W1 - Wiper Terminal
VCC - 3V or 5V Power Supply Input

RST - Serial Port Reset Input

CLK - Serial Port Clock Input
D - Serial Port Data Input
C

OUT

- Cascade Data Output
P0G,P1G - Gain Input Pot Controls
P0A,P1A - Attenuation Input Pot Controls

ZCEN - Zero-Crossing Detect Input

MUTE - Hardware Mute Control Input
AGND - Analog Ground
GND - Ground

DS1800

Dual Inverting Log Gain/Attenuato

r

www.dalsemi.com

GND 1 20 V

CC

C

OUT

219P1G
CLK 3 18 P1A
D 4 17 P0G
RST 5 16 P0A
ZCEN 6 15 MUTE
MODE 7 14 AGND
W0 8 13 IN1
OUT0 9 12 OUT1
IN0 10 11 W1

20-Pin DIP (300-mil)

20-Pin SOIC (300-mil)

20-Pin TSSOP

See Mech. Drawings Section

DS1800

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DESCRIPTION

The DS1800 is a dual audio-taper potentiometer designed specifically for use in the feedback path of the
inverting configuration of an operational amplifier (see Figure 2). In this configuration, the DS1800
provides a V

O

/VI relationship of -20log(R

F/RI

), giving a gain/attenuation range covering +20 dB to -63
dB. Each potentiometer has a total of 129 positions including mute. The DS1800 provides five areas of
resolution, which include: 0.25 dB per step from +20 dB to +3 dB; 0.5 dB per step from +3 dB to -12 d B;
1 dB from -12 dB to -27 dB; 2 dB per step from -27 dB to -47 dB; and 4 dB per step from -47 dB to -63
dB. The mute position provides 100 dB of attenuation.

The DS1800 has two control interfaces (see Figure 1). The first is a 3-wire serial CPU interface
consisting of RST , CLK, and D. The second interface is a contact-closure interface, allowing eas y push-

button control without the need for external debounce or timing circuitry. The device also provides for
software muting (via CPU) or hardware muting (MUTE control input). The hardware mute is a toggle
type which returns the wiper positions to their prior states. Additional information on CPU and push­button control is described under the section entitled “OPERATION.”

The DS1800 is available in 20-pin DIPs, SOICs, and TSSOPs. One standard resistance grade of 53 kΩ=is
available for the device.

OPERATION

The DS1800 provides two 129-position 45 kΩ potentiometers. These potentiometers are specifically
designed to operate in the configuration shown in Figure 2. Under this configuration the V0/VI
relationship provides the gain/attenuation function of -20log(RF/RI) over a range of +20 dB to -63 dB.
This function is illustrated in Figure 3 as a graph of gain/attenuation versus position. Figure 4 provides
the relationship between RF and RI as a function of position.

The DS1800 has a total of 129 positions including a mute position. Five areas of resolution are p rovided
over the gain/attenuation range and are illustrated in Figure 3. From position 0 to position 68, a resolution
of 0.25 dB per step is attained covering a gain/attenuation range of +20 dB to +3 dB. From position 68 to
position 98, 0.5 dB per step of resolution is attained covering +3 dB to -12 dB of gain/attenuation.
Positions 98 to 113 have 1 dB per step resolution and cover a gain/attenuation range of -12 to -27 dB.
Positions 113 to 123 provide 2 dB per step and cover a gain/attenuation range of -27 dB to -47 dB.
Positions 123 to 127 provide 4 dB per step and cover a gain/attenuation range of -47 dB to 63 dB.
Position 128 is the mute position and typically provides 100 dB of attenuation.

PIN DESCRIPTIONS

The DS1800 has a total of 20 pins which provide various functions for the device. This section provides a
description of each pin’s operation.

V

CC

- Power Supply Voltage Input. The DS1800 will support 3V or 5V power supply operation.

GND - Ground. The DS1800 has two ground pins. The GND supports the digital ground for the device.
AGND - Analo g Ground. The DS1800 has two ground pins. The AGND supports analog ground for the

device.

IN0, IN1 - Input terminals for the two respective potentiometers as shown in Figure 2. These terminals
should be connected to the analog signal, VI, to provide the gain/attenuation characteristics stated. These
terminals are referenced as INx in the Figure 2 drawing.

DS1800

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OUT0, OUT1 - Analog Outputs. These pins should be connected to the output terminal of the operational
amplifier as shown in Figure 2. These inputs are referenced as OUTx in the Figure 2 drawing.

W0, W1 - Wiper Terminals. The wiper terminals of each pot are connected to the inverting terminal of
the operational amplifier. The position of the wiper terminal is selected either through CPU control or
pushbutton control.

P0A, P1A - Attenuation Pushbutton Inputs. These pushbutton inputs are used to cont rol wiper position of
the part. Activity on these inputs will cause the position of the wiper to move towards the OUT0, and
OUT1 terminals, respectively.

P0G, P1G - Gain Pushbutton Inputs. These pushbutton inputs control wiper position and are used to
move the position of the wiper towards the IN0 and IN1 terminals, respectively.

RST - Seri al Port Reset. The RST input deactivates the 3-wire seri al interface. This input is active when

in the low state. All 3-wire communications must take place when this input is in a high state.
CLK - Serial Clock Input. The CLK input is the positive-edge clock signal input used for 3-wire timing

synchronization.

D - Serial Data Input. The D input is used to input serial data for wiper position changes.

C

OUT

- Serial Cascade Output. The C

OUT

is an output signal used to read the contents of the current

settings of the wiper positions. As data is clocked into the D input, data corresponding to the wipers are
shifted out of the C

OUT

pin.

MODE - Pushbutton Debounce Control. The MODE pin is used to choose between a fast and slow mode
of pushbutton debouncing. When in a high state, pushbutton debounce is slow. When in a low-state,
pushbutton debounce is faster. These timing differences are discussed in the section entitled “Pushbutton
Interface Control.” The state of this pin is determined only at device power-up.

POWER-UP CONDITIONS

The position of the wipers of the DS1800 on power-up are internally set to position 127, which is the last
position before mute. The user then has the responsibility of changing the wiper position to the desired
attenuation/ gain levels.

Additionally, the serial port is stable and active within 10 microseconds. The contact closure control
interface inputs are active after 50 ms.

INTERFACE CONTROL OPTIONS

Control of the DS1800 is provided via two types of interface ports. A 3-wire CPU control interface
allows the exact wiper positions of the potentiometers to be written using two 8-bit words. A cascade
output, C

OUT

, is provided when controlling multiple devices via one CPU or when reading the wiper

positions of each potentiometer.

The second interface is a contact closure interface that allows pushbuttons to control movement of the
wiper positions. Under pushbutton control no external debounce or timing circuitry is needed. A block
diagram of the DS1800 is shown in Figure 1.

DS1800

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3-WIRE SERIAL INTERFACE CONTROL

CPU control of the DS1800 is accomplished using the 3-wire serial port of the device. This interface
drives an internal control logic unit. Direct wiper positioning is accomplished by using this port which

consist of three input signals: RST , CLK, and D.

The RST control signal is used to enable 3-wire serial port write operations. The CLK terminal is an input
that provides synchronization for data I/O. Data is input bit by bit via the D input signal pin.

The 3-wire serial timing diagrams are provided in Figure 5. Serial port operation or activity begins with
the transition of the RST signal from a low state to a high state. Once acti vated, data is clocked into the

part on the low to high transition of the CLK signal input. Data input via the D terminal is trans ferred in
order of the desired potentiometer-0 wiper value, followed by the potentiometer-1 wiper position value.

Two 8-bit values are used to store wiper position for each potentiometer during powered conditions.
These 8-bit values are written to a 16-bit I/O shift register. A detailed diagram of the 16-bit I/O shift
register is shown in Figure 6.

Bits 0 through 7 are reserved for the positioning of wiper-0 while bits 8 through 15 are reserved for
control of wiper-1. Bits 0 through 6 are used for actual wiper positioning of potentiometer-0. Bit 7 is used
to mute potentiometer-0. If this bit is set to a 1, the potentiometer-0 wiper will be connected to the OUT0
end of the resistor array regardless of the settings of bits 0 through 6.

Bits 8 through 15 are used for positioning the wiper of potentiometer-1. Bits 8 through 14 control wiper
position on the resistor array. Bit 15 is used for muting potentiometer-1. Bit 15, like bit 7, when set to 1
will mute potentiometer 1, regardless of the settings of bits 8 through 14.

Data is transmitted LSB first starting with bit 0. A complete transmission of 16 bits of data is required to
insure proper setting of each potentiometer’s wiper. An incomplete transmission may result in undesired
wiper settings.

Once the 16 bits of information has been transmitted and the RST signal input transitions to a low state,
the new wiper positions are loaded into the part.

PUSHBUTTON INTERFACE CONTROL

The DS1800 can be configured to operate from contact closure or pushbutton inputs. The pushbutton
inputs consist of signals P0A, P0G, P1A, P1G and MUTE. P0A and P0G allow attenuation and gain
control of the input signal to potentiometer-0, while P1A and P1G provide the same control for
potentiometer-1. The MUTE input provides a toggle control for muting the potentiometers via
pushbutton.

The P0A and P1A control inputs, based on the recommended circuit configuration, are used to attenuate
the incoming signal by moving the wiper position towards the OUTx terminals. The P0G and P1G control
inputs provide the opposite function; positioning the wiper(s) closer to the INx terminals, thus providing
gain.

Each of these control inputs is internally pulled up via a 50 kΩ=resistance. Additionally, these inputs
require no external components for debouncing or timing which are provided internal to the part.

DS1800

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Contact closure is defined as the transition from a high level to a low level on thes e input terminals. The
DS1800 interprets input pulse widths as the means of controlling wiper movement. A single pulse input
over the PxA or PxG input terminals will cause the wiper to move one position. A transition from high to
low on these inputs is considered the beginning of pulse activity or contact closure. The DS1800 has two
timing modes for controlling the speed at which pushbuttons will operate. These modes are termed fast
mode operation and slow mode operation.

In slow mode operation, a single pulse is defined as being greater than 1 ms but lasting no longer than 0.8
seconds. Correspondingly, in fast mode operation, a single pulse is defined as b eing greater than 50 µs
but lasting no longer than 0.8 second.

Repetitive pulsed inputs can be used to step through each resistive position of the device in a relatively
fast manner. The timing requirements for repetitive pulsed inputs is that pulses must be separated b y a
minimum time of 1 ms for slow mode operation and 50 µs for fast mode operation.

Pulse inputs lasting longer than 0.8 seconds will cause the wiper to move one position every 25 ms
seconds after the initial 0.8 second hold time. This is true regardless of the mode input. The total time
required to transcend the entire potentiometer using a continuous input pulse is given by the following
formula:

0.8(seconds) + 127 x 25 ms = 3.975(seconds)

SLOW MODE AND FAST MODE OPERATION

Pushbutton operation, as mentioned, can be operated at two distinct speeds or modes; fast and slow. The
mode or speed of pushbutton debounce is determined at device power-up b y the state of the MODE pin.
When MODE powers to a high state, pushbutton debounce timing will operate at the slow mode rate.
When powered and in the low state, debounce timing operates at the fast rate. Timing specifications for
pushbutton operation can be found in the AC Electrical Specification Table for pushbutton operation.
Timing diagrams for pushbutton operation can be found in Figure 7.

ZERO CROSSING DETECTION

The DS1800 provides a zero-crossing detection capability when usin g the 3-Wire serial interface. Zero­crossing detection provides a means for minimizing unwanted audible noise that may result from sizable
discrete wiper transitions when using the part in audio applications. The zero-crossing detect feature
allows independent wiper changes only when the two terminals of the potentiometer(s) have equal

potentials and within a 50 ms time window from the fall of the

RST signal. If at 50 ms the DS1800 has

not detected a zero-crossing, the wiper position of the potentiometer(s) will change regardless of the state
of the input signal. Zero-crossing detection is activated when the ZCEN input is in a low-state. When high,
the

ZCEN input deactivates both the 50 ms time requirement and zero-crossing detection.

Zero-crossing detection is also available when using the part in pushbutton operation. When a pushbutton
is activated, the part will change wiper position during the first detected zero-crossing or at the end of a
50 ms time window.

When operating in pushbutton operation with a continuous input pulse, the wiper position will change
once during the initial 0.8-second time period. This change is dictated by a detected zero-crossing or 50
ms time window. Subsequent changes when operating with a continuous input pulse occur on 25 ms time
intervals and are dependent on zero-crossings or 50 ms time-outs.