LB1823 datasheet(9/11 Pages) SANYO

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8. FG amplifier

The FG amplifier gain is determined by R7 and R8, with the DC gain, G, being R8/R7. C9 and C10 determine the

FG amplifier frequency characteristics. (R7 and C9 form a high-pass filter and R8 and C10 form a low-pass filter.)

Since a Schmitt comparator is connected following the FG amplifier, the components R1, R2, C4 and C5 must be

chosen so that the amplitude is at least 250 mVp-p. (It is desirable that the FG output be set up to provide a level of

between 1 and 3 Vp-p during steady state motor rotation.)

9. Notes on external capacitors

• C8

C8 is required for stabilization of the FGIN+ pin constant voltage power supply and to generate the IC internal

logic reset pulse. The reset pulse is generated when the FGIN– pin reaches about 1.3 V from 0 V. If the reset does

not operate, the LD pin will go on briefly during IC start.

• C2

C2 is required for power supply stabilization. Since this IC adopts a PWM technique that switches large output

currents, it can generate noise extremely easily. Thus the power supply must be stabilized adequately so that this

noise does not cause the IC to operate incorrectly. C2 should be located as close as possible to pins 17 and 24.

10. Notes on external resistors

• R13, R14 and R15

These resistors set the external output (source side) transistor drive currents. The drive currents (ID) can be derived

from the following formula.

ID ≥ IOUT/hFE min

ID = (VCC – 0.7 – VO sat)/R

IOUT: Maximum output current

hFE min: Output transistor minimum current amplification factor

VO sat: The LB1823 output saturation voltage

• R16

R16 sets the shunt regulator bias current. R16 must be selected so that a current of over 1 mA flows in the VM

voltage range for which guaranteed correct operation is desired.

R16

≤ (V

M min – VREG)/1 mA

• R17, R18 and R19

R17, R18 and R19 prevent leakage from the lower side output transistors and make the switching time faster.

• R20

R20 prevents leakage from the integrator. A value of around 24 k

Ω is recommended. If this resistor is not used, the

INT OUT pin will go high in stop mode due to leakage currents. Startup is delayed by the integrator external time

constant at start time, since the motor is accelerated when the INTOUT pin is low.

11. External transistors

• Regulator transistor

Select a transistor with a current capacity of at least 70 mA and a breakdown voltage greater than the largest VM

voltage. Heat generation will be a problem. Use a heat sink or other cooling technique if required.

Pd = (VM max – VREG) × I

I: ICC + Hall bias current + output current (source) + α

When the internal shunt regulator is not used, the power supply must be connected directly to the VCC pin

(4.5 to 7 V). The regulator transistor is not required in this case.

2SC2314 (TO126), 2SD330 (TO220)

2SC3985 (TO220ML) or similar transistor

• Output interface transistors

These transistors are used to assure that high voltages are not applied to the IC. (The total system cost is lower by

restricting the IC breakdown voltage.) Select transistors with a current capacity of at least 30 mA and a breakdown

voltage greater than the largest VM voltage. (R13, R14 and R15 determine the currents.)

2SC4641 (NP), 2SC4640 (SPA)

2SC4520 (PCP), 2SC4211 (MCP) or similar transistors

No. 4263-9/11

LB1823

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