L7250

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2) A second approach is considering to have the VCM in stop position; to enable it in current mode con-

figuration driving current in the right direction in order to be sure to mantain the stop position; to decre-

ment the 15bit DAC value to reach the zero current condition using the 10bit ADC to measure the

current value.

In the following diagram a detailed flow chart is presented.

Figure 10. VCM Current Loop Offset Calibration 2

Set VCM inTristate

Write Reg.03H

VCMState[2:0] = 001

START

Current Mode “ZeroIout”

Calibration Routine

Set 15BitDAC to have VCM Current

with no motion

Write Reg.09H & Reg.0Ah

Dac[14:0] = DACvalue

Set the GainSw to High or Low

Set VCM in En.Current Mode

Write Reg.03H

VCMState [2:0] = 011

Call

IoutDigitalVal

Routine

Polarity check

ADC_DATA[9] = 0

Flag_A=0

EXIT

Current Mode “ZeroIout”

Calibration Routine

Yes

No

Flag_A=0

DACvalue=1200 ( 0x4B0 )

Note 1

DACvalue-=1

DACvalue<-1200

EXIT with Error 1

Calibration not performed

Positive offset to big

Yes

No

START 10Bit ADC Conversion

of the Iout Channel

Write Reg.0CH

ADC_CH_ADDR[1:0] =00

ADC_START=1

EXIT

IoutDigitalVal

Routine

Wait End of

Conversion

Read 10Bit ADC

Read Reg.0BH

ADC_DATA[9:2]

Read Reg.0CH

ADC_DATA[1:0]

YES

NO

START

IoutDigitalVal

Routine

Update the 15BitDAC

Write Reg.09H & Reg.0Ah

Dac[14:0] =DACvalue

Iout

Yes

StoreDACvalue

As reference for

ZEROIout

No

Flag_A=1

EXIT with Error 2

Calibration not performed

Negative offset to big

Wait 20msec

Call

IoutDigitalVal Routine

Iout_Offset = ADC_DATA[9:0]

Note 2

Note 1 : once the VCM will be enabled in current mode with the DAC value at 1200 the current will keep the motor against the crash stop position

Note 2 : with the VCM in tristate, the result of the digital conversion of the Iout Channel has to be used as ZERO current offset value

ADC_DATA[9:0] -= Iout_offset

( Subtract the offset )