LB11921T Datasheet, PDF (17/18 Pages) Sanyo Semicon Device – Monolithic Digital IC Three-Phase Brushless Motor Driver

LB11921T
18. R and C Pin External Components
The maximum range over which the reference signal frequency fVCO can be varied when 5V is used as the VCC
supply voltage is about a factor of three.
When it is desirable to make this range as wide as possible, since the values of the R pin external resistor (R) and the
C pin external capacitor (C) are determined by the maximum value of the reference signal frequency (fVCO1) and
the minimum value (VCCL) of the VCC power supply due to unit-to-unit variations, R and C can be determined
using the following procedure as a reference.
(1) Calculate R1 and C1 using the following formulas and determine values for R and C such that the conditions R ≤
R1 and C ≤ C1 will hold taking the sample-to-sample variations (including other issues such as temperature
characteristics) into account.
R1 = (VCCL-2.2 V)/370µA
C1 = (370µA /0.9V) × (1/fVCO1) × 0.7
(2) The minimum value (fVCO2) for the reference signal frequency that can be set for the R and C values determined
in step (1) can be calculated from the following formula if we let R2 and C2 be the smallest values for R and C
due to the sample-to-sample variations (including other issues such as temperature characteristics). Therefore, the
range over which the reference signal frequency can be set is fVCO1 to fVCO2.
fVCO2 = 0.38/(R2 × C2)
(3) The following are the conditions that must be met and the points that require care when determining the values of
the external components connected to the R and C pins.
1. The maximum value of the set reference signal frequency must not exceed 1.2MHz.
2. The R pin voltage and the FIL pin voltage must be in the range 0.3V to (VCCL-2.2V). (VCCL is the lowest
value of the VCC supply voltage given the unit-to-unit variations. VCCL is always greater than or equal to
4.4V.) However, the lower the R pin voltage, the more susceptible the system will be to ground line noise, and
the reference signal frequency may become unstable as a result. Therefore the lower end of the R pin voltage
range must not be used if there is much ground line noise in the system.
3. Set the value of the R pin external resistor to a value in the range 5.6kΩ to 10kΩ. Also, assure that the R pin
current remains under 370µA.
4. Set the value of the C pin external capacitor to a value in the range 220pF to 1000pF.
5. When it is desirable to make the range of the reference signal frequency as wide as possible, set the values of R
and C to the largest possible values. (However, those values must be lower than the calculated values R1 and
C1.) Use components with the smallest sample-to-sample variations possible. The VCC voltage must be made
as much higher than 5V as possible to acquire the widest possible range for the reference signal frequency.
19. NC pin
Since the NC pins are electrically open with respect to the IC itself, they can be used as intermediate connection
points for lines in the PCB pattern.
No.A0604-17/18