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Maxim > Design Support > Technical Documents > Application Notes > Digital Potentiometers > APP 3408
Keywords: internal calibration, ADC, A/D, gain, offset, temperature compensated, digital resistor, analog
monitors, EEPROM, SFF-8472
APPLICATION NOTE 3408
DS1856 Internal Calibration and Right Shifting
(Scalable Dynamic Ranging)
Dec 21, 2004
Abstract: This application note explains the internal calibration procedure for the DS1856, and how using
this function can be beneficial to the application. The application note also provides procedures for
determining and implementing the internal calibration and right-shifting features of the DS1856.
Introduction
The DS1856 uses internal calibration and right shifting (Scalable Dynamic Ranging) to enhance the built-
in 12-bit ADC. This gives the DS1856 the precision and accuracy of a 16-bit ADC without added size
and cost. Plus, the device's programmable gain and offset functions can reduce, or even eliminate the
need for external signal-conditioning circuitry. Once calibrated, these functions convert the analog input
signal to a digital value without requiring any action from the user.
The DS1856 functions similar to the DS1859, but has a memory map compatible with the DS1852
memory structure. The DS1856's internal calibration procedure is also quite similar to that for the
DS1859. (For examples of the DS1859 internal calibration, refer to Application Note 2858.) However, the
DS1856 has different Table assignments, as well as a slightly different equation for calculating the offset
register values.
This application note explains the internal calibration procedure for the DS1856, and how using this
function can benefit the application. This note also provides procedures for determining and
implementing the internal calibration and right-shifting features of the DS1856.
A Note about Password Access
The settings for the Scale and Offset values for the three MON inputs are located in Table 03 of the
DS1856. To read or write to these values, level-2 password access (PW2) is required. This access is
granted if the password for PW2 level entry is entered into the password entry bytes (PWE located in
addresses 7Bh-7Eh) using one, 4-byte WRITE command.
DS1856 Analog Monitor Inputs
Like the DS1859, the DS1856 has three analog inputs. These inputs, MON1, MON2, and MON3, can be
used to monitor such signals as Tx Power, Rx Power, and Tx Bias. The block diagram in Figure 1
shows the structure of the MON inputs.
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