SLFS040

– DECEMBER 1993

POST OFFICE BOX 655303

DALLAS, TEXAS 75265

11

PRINCIPLES OF OPERATION

VCM current-loop stability is accomplished using the filter at CMPI and CMPO. This filter has the following

transfer function:

(Rcmp

(Ccmp2 + Cmp1)

s + 1)

Ccmp2

s

(Rcmp

Ccmp1

s + 1)

where:

s is a Laplace operator

VCM retract

The TLS2205 integrated retract circuit eliminates the need for external power supply isolation devices. The

retract mode is triggered by the voltage monitor fault logic signal. The retract power path is coupled from the

spindle-motor back-EMF to the RETOUT MOS high-side driver via CRET. After the retract control block has

been triggered by a loss of power, the following events occur:

1.

outputs are disabled.

2.

The retract control circuit locks the VCMB low-side driver on and disables the VCMB high-side driver.

3.

The retract control circuit disables the VCMA low- and high-side drivers.

4.

RETOUT is enabled, and RETSET is used to control the voltage applied to RETOUT.

The spindle back-EMF-mode voltage supplies the energy necessary to retract the VCM (see Figure 3). The

devices. The value of this capacitor can be calculated based on ~ 2 A of retract-mode discharge current and

the time to retract

t the VCM. The RETOUT control equation is:

where:

Example:

Assume: Rrset1 = 62 k

Rrset2 = 100 k

t = 6 ms max

2 A

(5 ms)

0.7 V

(1 + 62 k /100 k )

= 0.009 F

0.01 F

t = 0.01 F

[0.7 V

(1 + 62 k /100 k )]

2 A

= 5.7 ms