AS8846 datasheet(29/35 Pages) AMSCO

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Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 29 of 35

Examples:

AV_RANGE_over = 1/4:

ACMV_over = 17.5, 17.75, 18, … , 20, … , 22.25 , 22.5

AV_RANGE_over = 4/4:

ACMV_over = 70, 71, 72, …, 80, … , 89, 90

The adjustment (trimming) of the measurement resistor Rmeas is realized by the same programming parameter AV_TRIMM (+

12.5%) like in a).

The maximal output voltage of the over current amplification channel VA_overc (this is the nominal input voltage of the ADC on the

µP) must be 4.0 V.

The threshold value of the over current detection can be programmed by the programming parameters OVERC_level (in

conjunction with AV_RANGE_over and AV_TRIMM) in the following way.

The voltage over the external measurement resistor where the over current situation is detected (Vmeas_over) is given by:

Vmeas_over = OVERC_level / (AV_TRIMM * AV_RANGE_over)

with OVERC_level = 0.5 V, 1.0 V, 1.5 V, … 4.0 V

See also section Summary of all programmable registers (parameters, functions) for the programming of the parameters

above.

PARAMETER

SYMBOL

MIN

MAX

UNIT

NOTE (Programming, nominal amplification)

- 6

+ 6

Vmeas = 50 mV, R8 = 0

à 80

- 10

+ 10

Vmeas = 25 mV, R8 = 1

à 160

- 20

+ 20

Vmeas = 16.67mV, R8 = 2

à 240

Tolerance of voltage

amplification, normal

current measurement

channel 1)

∆ACMV_normal

- 20

+ 20

Vmeas = 12.5 mV, R8 = 3

à 360

- 6

+ 6

Vmeas = 200 mV, R10 = 0

à 20

- 6

+ 6

Vmeas = 100 mV, R10 = 1

à 40

- 6

+ 6

Vmeas = 60.6 mV, R10 = 2

à 60

Tolerance of voltage

amplification, over

current measurement

channel 1)

∆ACMV_over

- 6

+ 6

Vmeas = 50 mV,

R10 = 3

à 80

Tolerance of linearity

ACMV_normal

∆lincurrent

- 3

+ 3

((

∆VA_current / ∆Vmeas_nom ) - ACMV_normal ) / ACMV_normal

Tolerance of linearity

ACMV_overc

∆linoverc

- 3

+ 3

((

∆VA_overc / ∆Vmeas_nom ) - ACMV_overc ) / ACMV_overc

Tolerance of over

current thresholds

∆overclevel

- 10

+ 10

R10 = 0, R9

≤ 3, Tamb > 25 oC

Tolerance of over

current thresholds

∆overclevel

- 20

+ 10

R10 = 0, R9

≤ 3, Tamb = -40 oC

Tolerance of over

current thresholds

∆overclevel

- 20

+ 20

R10 = 0, R9 > 3, Tamb = (-40 to 125) oC

Cut off frequency

fcut-off

400

800

kHz

Note (1):

The offset voltage of the current measurement unit at calibration temperature Vmeas_offset is < 1.5 mV

(typical: 0.5 mV), the maximal offset temperature drift is + 20

µV / K.

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