LV8771VH

No.A2056-7/13

Description of operation

Input Pin Function

The function to prevent including the turn from the input to the power supply is built into each logic pin.

Therefore, the current turns to the power supply even if power supply (VM) is turned off with the voltage impressed to

the input pin and there is not crowding.

(1) Chip enable function

This IC is switched between standby and operating mode by setting the ST pin. In standby mode, the IC is set to

power-save mode and all logic is reset. In addition, the internal regulator circuit and charge pump circuit do not

operate in standby mode.

ST

Mode

Internal regulator

Charge pump

Low or Open

Standby mode

Standby

Standby

High

Operating mode

Operating

Operating

(2) Output control logic

I01(02)

I11(12)

Output current (IO)

Low

Low

0

High

Low

IO = (( VREF / 5 ) / RF ) × 40%

Low

High

IO = (( VREF / 5 ) / RF ) × 70%

High

High

IO = ( VREF / 5 ) / RF

PH1(2)

Current direction

Low

OUTB → OUTA

High

OUTA → OUTB

(3) Setting constant-current control reference current

This IC is designed to automatically exercise PWM constant-current chopping control for the motor current by setting

the output current. Based on the voltage input to the VREF pin and the resistance connected between RF and GND,

the output current that is subject to the constant-current control is set using the calculation formula below:

IOUT = (VREF / 5) / RF resistance

* The above setting is the output current at I01(02) = High, I11(12) = Low.

(Example) When VREF = 1.5V, I01(02) = High, I11(12) = Low and RF1(2) resistance is 0.5Ω, the setting current is

shown below.

IOUT = (1.5V / 5) / 0.5Ω = 0.6A

(4) Chopping frequency control logic

FC

Chopping frequency

Low

31kHz

High

62kHz

(5) Blanking period

If, when exercising PWM constant-current chopping control over the motor current, the mode is switched from decay

to charge, the recovery current of the parasitic diode may flow to the current sensing resistance, causing noise to be

carried on the current sensing resistance pin, and this may result in erroneous detection. To prevent this erroneous

detection, a blanking period is provided to prevent the noise occurring during mode switching from being received.

During this period, the mode is not switched from charge to decay even if noise is carried on the current sensing

resistance pin.

The blanking time is fixed at approximately 1

μs.