Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 13 of 35

Programming of the motor current measurement unit and the over current detection unit

The chip has two measurement amplification channels with separately programmable amplification factors:

a)

normal motor current measurement, channel 1

b)

over current measurement with extended measurement range, channel 2

In general all programming possibilities in table 14 can be used to build up a measurement system in the defined limits. The

programming words are sent from the

µP via the Three-Wire Interface to the AS8446 during start up of the system. The typical

In the whole system the analog outputs A_current or A_overc are used by the ADC of the

µP to regulate and control the

system. There is only one exception: The over current detection and protection is realized directly by the over current

measurement channel in order to act very fast in case of an over current situation e.g. short circuit of the motor.

Figure 8 Programming examples of the current

Figure 9 Programming examples of the over current

measurement channels

detection

Figure 8 shows the programming of the normal current measurement channel (red lines, output voltage VCUR) and the over

current measurement channel with extended measurement range (blue lines, output voltage VCOVER). The three lines with the

parameters AV_TRIMM = 70, 80, 90 indicate the trimming range of the external measurement resistor (+ 12.5 % in steps of 1.25

Figure 9 shows an example of the programming of the over current threshold level (generation of the over current signal VPOV,

All programming possibilities are given in table 14 below.