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Maxim > Design Support > Technical Documents > Application Notes > A/D and D/A Conversion/Sampling Circuits > APP 233
Maxim > Design Support > Technical Documents > Application Notes > Digital Potentiometers > APP 233
Maxim > Design Support > Technical Documents > Application Notes > Optoelectronics > APP 233
Keywords: digital resistor, digital pot, digital potentiometer, digipot, DS1847, DS1848, potentiometers
APPLICATION NOTE 233
Regenerating the DS1847/DS1848 Resistor
Calibration Constants
Mar 10, 2003
Abstract: The purpose of this application note is to show how the DS1847/48 digital resistor calibration
constants can be regenerated. This application note assumes that the reader is familiar with the
Programming the Lookup Table section of the DS1847 or DS1848 data sheets. This application note will
describe the measurements required, as well as show the calculations needed to regenerate the
calibration constants. Last of all, this application note will show an example spreadsheet calculator (a link
to it can be found at the end of this application note) that can be used to perform the calculations once
several measurements are input.
Introduction
The DS1847/48 resistor calibration constants are calculated and programmed into EEPROM at the
factory during two test steps that are performed at different temperatures (25°C and 95°C). These
calibration constants are unique and vary from device to device as well as lot to lot. Unfortunately, at the
time the DS1847/48 was designed, the use of calibration constants was not considered and therefore
additional write protected or read-only memory for the constants was not included. So when the decision
was made to include them, the only location for them to be stored (at least for the DS1847) was in the
Lookup Tables (LUTs). The obvious problem here is that when the user fills the LUTs, the factory
programmed calibration constants are overwritten. Fortunately for the DS1848, a copy of the calibration
constants (although not write protected) is also stored in the user EEPROM (Table 0). If using the
DS1848, it may be worthwhile to check if the calibration constants are still intact in the user EEPROM
before reading further.
The purpose of this application note is to show how the DS1847/48 calibration constants can be
regenerated. This application note assumes that the reader is familiar with the Programming the Lookup
Table section of the DS1847 or DS1848 data sheets. This application note will describe the
measurements required, as well as show the calculations needed to regenerate the calibration constants.
Last of all, this application note will show an example spreadsheet calculator (a link to it can be found at
the end of this application note) that can be used to perform the calculations once several measurements
are input.
Convention
The conventions used to represent the calibration constants in this document are as follows:
Upper case calibration constants (U, V, W, X, Y, and Z) are the integer values read from the part
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