TSS400-S2

µPOWER PROGRAMMABLE HIGH-PRECISION

SENSOR SIGNAL PROCESSOR

SLMS002 – D4101, OCTOBER 1993

9

POST OFFICE BOX 655303

measurement range and conversion formulas (continued)

battery check

Since the TSS400-S2 is ideal for battery applications, an internal supply voltage check is available. This

operation is executed by the instructions ADJBATT and CHKBATT. ADJBATT measures the internal reference

voltage and puts the results in the FLAC register. By setting the supply voltage at a minimum acceptable level

and executing the ADJBATT instruction, a representative value is placed in the FLAC register. Saving this

number in a storage register or EEPROM location enables it to be recalled for use by the CHKBATT instruction

when the current supply voltage needs to be checked against the preset acceptable minimum. To perform these

operations, an internal stable reference is connected to the input of the ADC and a measurement is made. Due

to the ratiometric nature of the conversion, the measured value is an indication of the TSS400-S2 supply voltage.

The ADJBATT instruction performs this operation and stores the result in the FLAC register. The CHKBATT

instruction performs the same operation but compares the resulting measurement to the number in the FLAC

register and sets the positive ( POS ) and negative ( NEG ) status bits according to the result.

programmable current source

sensors. When turned on, the current source sends a constant current out of the addressed analog input ( An ).

The voltage generated by the external sensor is measured with the same An input. The voltage used for A / D

current source is off. Figure 3 shows a diagram of the programmable current source.

is given by the following equation:

I

V

Rext

The programmable current range that the current source can supply to the ADC input is:

0.15 mA to 2.4 mA

V

I

An

R

I

with R

sensor resistance

V

V

Rext

R

I