LB1860 datasheet(3/8 Pages) ONSEMI

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Block Diagram and Application Circuit

Truth Table

(

): LB1860M, 1861M

–

Rt1

Rt2

OUT1

OUT2

Mode

—

Full speed

—

Full speed

(H)

(L)

—

(H)

(L)

(H)

(L)

(Full speed)

(L)

(H)

—

(H)

(L)

(H)

(L)

(Full speed)

—

Low speed

—————

HHHH

Lock protection

Designer’s Notes

(1) Variable-speed circuit (Rt and Ct pins) — Refer to the application circuit diagram

The time constant gained by external components C2 and R2 is used to set the length of an ‘off’ operation time period after

phase switching. This means that the variable-speed operations can be performed by changing the ‘on’ operation time of each

phase through the duty control.

The sawtooth waveform signals are generated by the C2-R2 time constant. The voltage of this signal (Ct pin voltage) increases

from 1.3 V to 4.0 V (Vct) at each phase switching. That is, during this period, the driver becomes inactive (toff), in which

output circuit is turned off.

If VCC ^ 4.0 V, the driver IC remains active (ton) until the next phase switching. During this period, output circuit is turned on.

If the active drive time of each phase is assumed to ‘to’, the following relation can be established:

to =toff +ton

↑↑

Fixed

Rotation speed

constant

proportional constant

toff = 0.69 c C2 c R2 ........................................ 1

Constant

current

circuit

Output timing control

Unit (resistance:

Ω, capacitance: F)

Figure 1

(

): MFP14S

0.47 to 10 µ

LB1860,1860M,1861,1861M

No. 3

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