Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 14 of 35

Programming of the motor current measurement and over current detection unit

The motor current measurement unit transforms the differential voltage over the measurement resistor at the high side

unit:

Register No

Register Name

Meaning

R7<4:0>

AV_TRIMM

Voltage amplification factor1 of the current measurement unit in

small steps (trimming of the external current measurement resistor)

for the normal and over current analog measurement output

R7 = 0

à AV_TRIMM = 70

R7 = 1

à AV_TRIMM = 71

R7 = 2

à AV_TRIMM = 72

:

R7 = 10

à AV_TRIMM = 80

(default value)

R7 = 11

à AV_TRIMM = 81

:

R7 = 19

à AV_TRIMM = 89

R7 = 20

à AV_TRIMM = 90

R7 > 20

à AV_TRIMM = 90

R8<1:0>

AV_RANGE

Voltage amplification factor2 of the normal analog measurement

output (A_current)

R8 = 0

à AV_RANGE = 1

(default value)

R8 = 1

à AV_RANGE = 2

R8 = 2

à AV_RANGE = 3

R8 = 3

à AV_RANGE = 4

R9<2:0>

OVERC_level

Threshold value of the internal over current detection

Def.: Vocmax = 4/5 * VDD

(typ. 4.0 V)

Vocstep = (4/5 * VDD) / 8

(typ. 0.5 V)

R9 = 0

à OVERC_level = Vocmax

(typ. 4.0 V)

R9 = 1

à OVERC_level = Vocmax – Vocstep

(typ. 3.5 V)

R9 = 2

à OVERC_level = Vocmax - 2*Vocstep

(typ. 3.0 V)

R9 = 3

à OVERC_level = Vocmax - 3*Vocstep

(typ. 2.5 V)

:

R9 = 7

à OVERC_level = Vocmax - 7*Vocstep

(typ. 0.5 V)

R10<1:0>

AV_RANGE_over

Voltage amplification factor2 of the over current analog

measurement output (A_overc)

R10 = 0

à AV_RANGE_over = 1 * 1/4

(default value)

R10 = 1

à AV_RANGE_over = 2 * 1/4

R10 = 2

à AV_RANGE_over = 3 * 1/4

R10 = 3

à AV_RANGE_over = 4 * 1/4

Remark 1: The maximum of the valid analog output voltage of the outputs A_current and A_overc must be 4.0 V.

Remark 2: The total voltage amplification of the current measurement unit is determined by

(default value: 80)

(default value: 20)