Figure 14. Back EMF Phase Detection Timing Relantionships

TRANSITIONS

Transitioning from blind table drive to a back EMF mode drive is handled in the following manner. Re-

member, data written to the CPR takes effect only when SP_CLK receives a positive transition. The fol-

lowing steps must be taken:

● The programmer must ensure that the last state before state 0 has been output to the CPR and

clocked in using SP_CLK.

● An all 1’s value is written to the CPR to enable the state counter.

● The next SP_CLK will then produce a state 0 from the sequencer.

Voice Coil Driver (Vcm) Section

VCM SECTION SPECIFICATIONS

Parameter

Test Conditions

Min.

Typ.

Max.

Units

Large Signal Voltage gain

Output Swing from 1 to

10V

70

dB

Gain Bandwidth Product, A-Amp

4.5

MHz

3dB BW, total loop

25

kHz

Phase Margin, A Amp

45

°

Slew Rate, A Amp

1.4

2

V/

µs

Gain, B Amp

-1.17

*A gain

3dB Bandwidth, B

2.3

MHz

Total A+B saturation Resistance

I = 600mA

2

3

Ω

D/A reg @ 0

30

mV (1)

Vpwr/2 Input Impedance

25°C

38

50

65

k

Ω

Loopback Output Threshold (2)

25°C

50

mA/

Ω

Output saturated either

polarity

30

50

70

mV

(1) Total current offset of VCM loop must not exceed 3% of full scale current.

(2) Optional.

L6256

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