1999 June 10

18

Philips Semiconductors

Preliminary specification

5 V spindle & VCM driver combo

TDA5345HT

Spindle current loop

loop input is controlled by the internal FLL/PLL speed loop. The transconductance is defined by the following formula

(see Fig.3) :

(1)

The spindle current loop bandwidth is given by the following formula : (gm means transconductance : di/dv)

(2)

the BandWidth => the bandwidth is maximum at Start-Up.

To make sure that the OTA output is 0V when Run/Stop bit = ‘0’, a 30 mV (typ.) offset is introduced inside the OTA. By

this way, we make sure that SpinCompens external capacitor is kept discharged until the next start-up.

Spindle FLL/PLL speed loop :

An internal speed loop is provided, intended to work with 12 poles spindle motors. It is mainly composed of a Frequency

Locked Loop. A Phase Locked Loop can be associated when bit 9 in register #5 (PllOn/Off) is ‘1’. The typical FLL charge

pump current is 500

µA while the typical PLL charge pump current is given in table 7 :

Table 7

PLL charge pump typical current (PllCur[1,0] are bits 8 & 7 in register #5):

A 15-bit division factor (Speed[14, 0]) is used to set the required speed split in bits [11, 9] in register #5 and bits [11, 0]

in register #6:

The Speed[14, 0] division factor can be calculated by :

(3)

Where CLOCK is between 10 MHz and 33 MHz.

When the spindle is not running (Run/Stop = ‘0’) the FLL charge pump discharge current is active so that the external

filter is discharged before the next start-up. When the spindle is running (Run/Stop = ‘1’), the speed can be continuously

monitored on pin SpinMechClock (1 pulse per revolution / 50% duty cycle waveform).

SPINDLE / VCM 6-bit current DAC:

An internal 6-bit current DAC is used to limit the spindle start-up current (bit 6 in register #5 : Dac6ToVcm = ‘0’) or to

cancel the VCM loop offset ( Dac6ToVcm = ‘1’).

PLLCUR[1,0]

PLL CH. PUMP CURRENT

00

0.25

µA

01

0.5

µA

10

0.75

µA

11

1

µA

G

Spin

A

( )

V

( )

⁄

[]

∆I

Spin

∆V

SpinSpeedFilter

---------------------------------------------

530

R

SpinLoopGain

------------------------------------

530

1700

Ω

------------------

312mA V

⁄

=

=

==

BW

SpinCurLoop

gm

OTA

R

SpinLoopGain

530

------------------------------------

×

gm

NMOS

×

2

π

⋅

C

×

SpinCompens

--------------------------------------------------------------------------------------------

65.5 10

6

–

⋅

I

Spin

C

SpinCompens

------------------------------------

×

=

=

Speed 14 0

,

[]

5

3

---

CLOCK

SpindleSpeed rpm

()

-------------------------------------------------------------

×

=