Si9993CS

Vishay Siliconix

FaxBack 408-970-5600, request 70653

S-60752–Rev. A, 05-Apr-99

www.siliconix.com

13

Power-Up Sequence

The POR timer receives the two supply undervoltage

detection outputs and combines them to form one output

called PowerFailure. If PowerFailure is low, the POR output

will remain low. After the power supplies are deemed safe,

PowerFailure goes high and the timer is turned on which holds

the POR output low for an additional 500 ms. If PowerFailure

goes back low while the timer is active, the POR output must

remain low and the timer must reset and wait for PowerFailure

to go back high before starting again.

The POR output must drop low within 1

µs from when a power

failure is detected. Once the POR output drops low, the timer

must also reset. If the PowerFailure output drops low for less

than 600 ns, then the power failure is ignored and the POR

output remains high and the timer is not reset. The POR

output cannot glitch at anytime. If a power failure is detected,

then the POR output must stay low for a minimum of 350 ms.

A minimum of 1 V of hysteresis exists at the POR comparator

which monitors the timer ramp voltage.

Recommended Parameter Setting Hardware Values and

Register Contents

Spindle

In order to perform some applications testing, some of the

registers should be preloaded and certain hardware values

installed. These are for a first approximation on an average

spindle motor and should be adjusted for the particular motor

and parameters that will be used.

All registers will default to 0 at power-up. The following

register value exceptions should be loaded for an average

motor load.

For start-up:

REG3 D7

→D0 = 00000011; 8° Phase Advance, 13-µS PWM

Off-Time

REG4 D7

→D0 = 00000000; 1.4-µS On-Time Blanking, 7/8

Off-Time, Slew Rate Off, Q-COM Off

REG5 D2

→D0 = 000; 400-ns F/I Sample Time, F/I Speed-Up

On

After reaching speed:

REG3 D7

→D0 = 00000001; 8° Phase Advance, 3.4-µS PWM

Off-Time

REG4 D7

→D0 = 00000111; 1.4-µS On-Time Blanking, 7/8

Off-Time, Slew Rate On, Q-COM On

REG5 D2

→D0 = 110; 40-ns F/I Sample Time, F/I Speed-Up

On

Hardware values:

Resistor from SRADJ to Ground = 20 k

Ω for approximately

1-

µS Slew Rate

VCM

The Si9993CS contains a transconductance amplifier to drive

the voice coil motor (VCM). For proper operation, this

amplifier must be compensated specifically for the VCM being

driven. As a first approximation, the torque constant and

inertia of the VCM may be ignored although they will have

some influence on the final results, especially if large.

The VCM transfer function of this simplified case may be

expressed in the s (Laplace) plane as:

Where

s is the Laplace operator

the interest of stability. In order to do this, a compensation

amplifier is cascaded with the VCM and its driver. The transfer

function of this amplifier is:

Where

A = compensation amplifier and driver voltage gain at high frequency

transconductance in siemens becomes:

Use these values as the series combination from COMP1 to

COMP2. The absolute values should be adjusted for the

desired open loop gain and closed loop bandwidth desired.

This has a single pole at the origin and is therefore stable

when the loop is closed.

g

v

1

L

v

-----

s

R

v

L

v

------

+

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

=

(1)

H

c

A

s

1

R

L

C

L

+

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

+





s

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

×

=

(2)

g

to

A

sL

v

×

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

=

(3)