ML4425IP datasheet(8/16 Pages) MICRO-LINEAR

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ML4425

OUTPUTS

INPUT

STATE

SAMPLING

OFF

N/A

OFF

FB B

OFF

FB A

OFF

FB C

OFF

FB B

OFF

FB A

OFF

FB C

Table 1. Commutation State Functions

Figure 4. Output Commutation Sequence Timing Diagram

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

HIGH

SIDE

DRIVE

OUTPUTS

LOW

SIDE

DRIVE

OUTPUTS

ABC

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

(VCO constant, Kv) is set by an 80.6kW resistor on RVCO

and a capacitor on CVCO as shown in Figure 5. RVCO sets

up a current proportional the VCO input voltage at SPEED

FB. This current is used to charge and discharge CVCO

between the threshold voltages of 2.3V and 4.3V. The

resulting triangle wave on CVCO corresponds to the clock

on VCO. Kv 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 VREF. CVCO is calculated

using the following equation:

Hz Farad

RPM

NSPEED

VCO

MAX

6 5

3101 10

005

(2)

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

calculated CVCO should be used.

FUNCTIONAL DESCRIPTION (Continued)

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