LV8814J Datasheet, PDF (17/36 Pages) ON Semiconductor – Motor Driver 3-Phase PWM Full-Wave BLDC

LV8811G, LV8813G, LV8814J
ROTATIONAL CONTROL PIN BY DC VOLTAGE (VTH)
This pin reads the input DC voltage and controls
rotational speed. The VTH voltage is compared with the
CPWM triangle wave with an internal comparator and
generates PWM pulse and controls rotational speed with
frequency and duty cycle of this pulse.
If the external control signal is the pulse type, it should
be flattening by the filter and be shifted to suitable level.
The external circuit example is shown in Figure 4.
VTH input level flatten by the filter is calculated in the
following equation.
V_VTH
=
V_REG
×
�^R15_R+A^R16
−
R₁₄
R_A
×
×
R₁₆
R_B
×
D1_P0W0M�
Where
R_A = R₁₄ + R₁₅ + R₁₆
R_B = R₁₄ + R₁₅
V_VTH = VTH input level
This calculation is justified by the condition that Rds of
MN1 << R₁₆. So, a large value of resistor should be
selected to R₁₆.
For example, when the input PWM duty cycle is set in
50%, can be determined by follows.
50[%]
V_VTH = 3[V] × (0.698 − 0.498 ×
)
100
V_VTH = 1.35[V]
Where
R₁₄=7.5[kΩ], R₁₅=30[kΩ], R₁₆=62[kΩ]
Figure 27. Equivalent circuit of VTH
NC PIN (NC)
This pin is not connection to the internal circuit.
The cut-off frequency fc by C₄ and R₁₈ is calculated in
the following equation.
1
f_c = _{2𝜋𝜋 × 𝐶𝐶4 × 𝑅𝑅18}
The actual value of C₄ or R₁₈ is better to select more than
50 times the above calculation value to be flatten
thoroughly. Furthermore, it is better to do it by the value
of C₃ because of the effect of input impedance at VTH
pin.
If the external control signal is the DC type, it inputs
into direct VTH pin. However, It is recommended that
the filter (C₄ and R₁₈) is kept because rid of the influence
of the noise.
The CPWM amplitude is decided by VREF. Thus, VTH
recommends that it is made from V_REG. The
combination with the rotational speed control by PWM
is impossible. When the pin is not used, it must be
OPEN. Refer ‘PWM duty CYCLE control by analog
voltage’ on page 26. (Figure 27)
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