ML4425

PRODUCT SPECIFICATION

8

REV. 1.0.2 7/2/01

Voltage Controlled Oscillator (VCO)

The VCO provides a TTL compatible clock output on the

VCO/TACH pin proportional to the VCO input voltage at the

SPEED FB pin. The proportion of frequency to voltage

a current proportional the VCO input voltage at SPEED FB.

the threshold voltages of 2.3V and 4.3V. The resulting trian-

should be set so that the VCO output frequency corresponds

to the maximum commutation frequency or maximum motor

speed when the VCO input is equal to or slightly less than

The closest standard value that is equal to or less than the

C

VCO

6.5V

3.101

×

10

6

–

Hz

Farad

•

V

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

×

0.05

Hz

RPM

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

N

×

SPEED

MAX

×

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

=

(2)

Table 1. Commutation State Functions

State

Outputs

Input

Sampling

LA

LB

LC

HA

HB

HC

R

OFF

ON

OFF

ON

OFF

ON

N/A

A

OFF

OFF

ON

ON

OFF

OFF

FB B

B

OFF

OFF

ON

OFF

ON

OFF

FB A

C

ON

OFF

OFF

OFF

ON

OFF

FB C

D

ON

OFF

OFF

OFF

OFF

ON

FB B

E

OFF

ON

OFF

OFF

OFF

ON

FB A

F

OFF

ON

OFF

ON

OFF

OFF

FB C

Figure 4. Output Commutation Sequence Timing Diagram

Cycle 1 – Full Commutation, Cycle 2 – Commutation with 50% PWM Duty Cycle

HIGH

SIDE

DRIVE

OUTPUTS

HA

HB

HC

LOW

SIDE

DRIVE

OUTPUTS

LA

A

B

C

D

EFA

B

C

D

E

F

LB

LC