DS1852

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ANALOG-TO-DIGITAL CONVERTER

are absolute and compared to an internal reference. While the 16-bit values are read, only the upper 12

are significant. The lower four bits are undefined.

The temperature and analog voltage inputs are calibrated by Dallas Semiconductor and read with the

following scale:

Temperature: High byte: -128

°C to +127°C signed; low byte: 1/256°C. The lower four bits

should be ignored.

mV LSB, with a maximum range of

6.5535V, when using the factory default value. The lower four bits should be ignored.

mV LSB, with a maximum range

of 2.500V, when using factory default values. The lower four bits should be ignored.

Each analog input has a 16-bit scaling calibration in Table 03h EEPROM. This allows the analog

conversion values to be calibrated for full scale at any input voltage from 0.2V to 6.5535V. The ADC

conversion value will clamp rather than roll over. Each external analog channel has a maximum input

The upper four bits of scaling select the coarse range; the lower 12 bits are for fine adjustments. The

algorithm to trim the scale is described below.

Table 03h at addresses C8h to CFh, respectively. The 16 bits are a combination of two trims. The lower

12 bits are binary weighted and give the high resolution trim for scaling the input to output relationship.

The upper four bits are a coarse-adjust of the lower 12 bits. In other words, the upper four bits scale the

LSB value of the binary weighted lower 12 bits.

As an illustration, assume a value of 1V is needed to read full scale. Force a voltage less than 1V

(975mV, for example) to keep clamping out of the way. The closer to max voltage the better, but not too

close.

1) Set the scale trim to 0FFFh (the upper four bits to all zeros and the lower 12 bits to all ones).

2) Use a SAR approach on the upper four bits, starting with 1000b, to find the smallest 4-bit trim

necessary to cause the voltage reading to be above the input (in this case, greater than or equal to

975mV). If they all clamp, that is okay. That means 0000b is the needed value for the upper four