DS1800 Datasheet, PDF (2/14 Pages) Dallas Semiconductor – Dual Inverting Log Gain/Attenuator

DS1800
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 /V_I relationship of -20log(R_F/R_I), 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 dB;
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 easy 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 push-
button 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(R_F/R_I) 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 R_F and R_I as a function of position.
The DS1800 has a total of 129 positions including a mute position. Five areas of resolution are provided
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 - Analog 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.
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