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LB11852FV-W-AH

P1-P3P4-P6P7-P9P10-P12P13-P13
LB11852FV
www.onsemi.com
10
2. Supplementary description of operations
By inputting the duty pulses, a feedback loop is formed inside the LB11852 IC to establish the FG period (rotational
speed of the motor) that corresponds to the control voltage of the pulses.
The operation inside the IC is as flows. pulse signals are created from the edges of the FG signals as shown in the
figure below, and using these signals as a reference, waveforms with a pulse width determined by the CR time constant
are generated using a one-shot multivibrator. These pulse waveforms are then integrated to control the duty ratio of the
pre-driver output as the control voltage.
By changing the pulse width as determined by the CR time constant, the VCTL versus rotational speed slope can be
adjusted as shown in the speed control diagram in the previous section.
However, since pulses that are determined by the CR time constant are used, the CR variations are output as-is as the
speed control error.
CTL
Signal
CTL
FG
LB11852
Closed
Feed-Back
Loop
CONTROL
SIGNAL
Speed
control block
Pre-driver
block
One-shot
multivibrator
output
RC pin
Edge pulse
FG
TRC (sec) = 1.15RC
Slope determined
by CR time
constant
LB11852FV
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11
4. Procedure for calculating the constant
RC pin
The slope shown in the speed control diagram is determined by the constant of the RC pin.
1) Obtain the FG signal frequency fFG (Hz) at the maximum rotational speed of the motor
(with two FG pulses per rotation).
fFG (Hz) = 2 rpm/60
(1)
2) Obtain the time constant of the components connected to the RC pin
(use the duty ratio (example : 100% = 1.0 or 60% = 0.6) as the CTL duty ratio for achieving the maximum rotational
speed).
R C = Duty ratio/ (3.3 1.1 fFG)
(2)
3) Obtain the resistance and the capacitance of the capacitor.
Based on the discharge capability of the RC pin, the capacitance of the capacitor which can be used is in the range of
0.01F to 0.015F.
Therefore, obtain the appropriate resistance from the result of (2) above using the formula in (3) or (4) below.
R = (R C)/0.01F
(3)
R = (R C)/0.015F
(4)
The temperature characteristics of the curve are determined by the temperature characteristics of the capacitor of the
RC pin. To minimize the variations in the rotational speed caused by temperature, a capacitor with excellent
temperature characteristics must be used.
(RPM)
Motor
at maximum speed
0%
100%
CTL Duty(%)
LB11852FV
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12
LIM pin
The minimum speed is determined by the voltage of the LIM pin.
1) Obtain the ratio of the minimum speed required to the maximum speed.
Ra = Minimum/maximum speed
(1)
In the example shown in the figure above : Ra = minimum/maximum speed = 3000/10000 = 0.3
2) Obtain the product of the duty ratio at which the maximum speed is achieved and the value in formula (1).
Ca = Maximum speed duty ratio Ra
(2)
In the example given : Ca = maximum speed duty ratio Ra = 0.8 0.3 = 0.24
3) Obtain the required LIM pin voltage.
LIM = 5 - (3 Ca)
(3)
In the example given : LIM = 5 - (3 Ca) = 5 - (3 0.24) 4.3V
4) Divide the resistance of 5VREG to generate the LIM voltage.
In the example given, the voltage is 4.3V so the resistance ratio is 1 : 6.
The resistance is 10k between 5VREG and LIM and 62k between LIM and GND.
(RPM)
Maximum speed
Minimum
speed setup
8000
10000
6000
4000
2000
0%
5V
100%
2V
CTL Duty(%)
CVO pin voltage (V)
VREF
LIM
5VREG
SOFT
P1-P3P4-P6P7-P9P10-P12P13-P13

LB11852FV-W-AH

Mfr. #:
Buy LB11852FV-W-AH
Manufacturer:
ON Semiconductor
Description:
Motor / Motion / Ignition Controllers & Drivers SINGLE PHASE PRE-DRIVER
Lifecycle:
New from this manufacturer.
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