LB11923V Datasheet, PDF (19/20 Pages) Sanyo Semicon Device – Three-Phase Brushless Motor Driver

LB11923V
17. Integrating Amplifier
The integrating amplifier integrates the speed error pulses and the phase error pulses and converts them to a speed
command voltage. At the same time it also sets the control loop gain and frequency characteristics using external
components.
The integrating amplifier output (pin 15) is normally connected to the TOC pin (pin 16) using external wiring. In
cases where it is necessary to switch the integration constant in an application that uses a wide speed range by
isolating the integrating amplifier output and the PWM control circuit, this type of constant switching application can
be implemented by adding external operational amplifier, analog switch, and other components.
In either case, the basic idea is that the operational amplifier output is connected to the TOC pin. (Note that voltages
in excess of V_CC – 0.5 V must not be applied to the TOC pin.)
18. FIL Pin External Components
The capacitor inserted between the FIL pin and ground is used to suppress ripple on the FIL pin voltage. Therefore,
application designers must select a capacitance value that provides fully adequate smoothing of the FIL pin voltage
even at the lowest external clock input frequency used. Also, the FIL pin voltage convergence time (the time until the
reference signal stabilizes) when the input clock frequency is switched is shortened by connecting a resistor and a
capacitor in series between the FIL pin and ground. Therefore, designers must select values for the resistor and
capacitor that give the required convergence time.
19. R and C Pin External Components
The maximum range over which the reference signal frequency f_VCO can be varied when 5 V is used as the V_CC
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 (f_VCO1) and the
minimum value (V_CCL) of the V_CC 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 = (V_CCL – 2.2 V) / 280 µA
C1 = (280 µA / 0.9 V) × (1/f_VCO1) × 0.7
(2) The minimum value (f_VCO2) 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 f_VCO1 to f_VCO2.
f_VCO2 = 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 MHz.
2. The R pin voltage and the FIL pin voltage must be in the range 0.3 V to (V_CCL – 2.2 V). (V_CCL is the lowest
value of the V_CC supply voltage given the unit-to-unit variations. V_CCL is always greater than or equal to 4.4
V.) 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 6.8 kΩ to 15 kΩ. Also, assure that the R pin
current remains under 280 µA.
4. Set the value of the C pin external capacitor to a value in the range 150 pF to 1000 pF.
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 V_CC voltage must be made
as much higher than 5 V as possible by, for example, using this IC’s VREG pin (7 V shunt regulator), to
acquire the widest possible range for the reference signal frequency.
No. 7498-19/20