1999 June 10

19

Philips Semiconductors

Preliminary specification

5 V spindle & VCM driver combo

TDA5345HT

When the 6-bit DAC is used for the spindle, the LSB current is set externally, by means of a 33 k

Ω resistor (to have a

very good absolute accuracy). The Spindle Current limit is then set by 31 steps of 20 mA. Please note that only the

Table 8

Spindle Start-up current limit according to the spindle 6-bit DAC code :

When the 6-bit DAC is used for the VCM section, the LSB current is set by an internal resitor to have a good matching

with the 2 internal resistors used to set the VCM loop Gain. The VCM current offset is set by steps of :

(4)

Table 9

VCM driver

The VCM is a linear, AB class type with both low-side and high-side drivers configured as a H-bridge. The zero-current

to be measured through the sense amplifier. The gain of the sense amplifier is internally set to typically 3. The output

VcmSenseOut is given by the following equation:

(5)

Figure 14 presents the VCM sense amplifier.

INPUT CODE

SPINDLE START-UP CURRENT

000000

0 mA

000001

20 mA

011111

620 mA

INPUT CODE

VCM OFFSET CURRENT

011111

+50 mA

000000

0

µA

1111111

-1.613 mA

100001

-50 mA

100000

-50 mA

I

VCMOffset LSB

()

1.613 10

3

–

⋅

R

Sense

------------------------------- A

( )

=

VcmSenseOut

3

VcmSenseInP

VcmSenseInM

–

(

) VcmRef

+

×

=

VcmSenseInP

VcmSenseInM

+

-

Fig.11 VCM sense amplifier

R

R

3R

3R

VcmRef

R = 10 k

Ω

23

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