LB1860 查看數據表（PDF） - ON Semiconductor
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LB1860 Datasheet PDF : 9 Pages
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LB1860, LB1860M, LB1861, LB1861M
Designer’s Notes
.(1) Variable-speed circuit (Rt and Ct pins) — Refer to the application circuit diagram
The time constant gained by external components C2 and R2 is used to set the length of an ‘off’ operation time period after
phase switching. This means that the variable-speed operations can be performed by changing the ‘on’ operation time of each
. phase through the duty control.
The sawtooth waveform signals are generated by the C2-R2 time constant. The voltage of this signal (Ct pin voltage) increases
.. from 1.3 V to 4.0 V (Vct) at each phase switching. That is, during this period, the driver becomes inactive (toff), in which
output circuit is turned off.
If VCC 4.0 V, the driver IC remains active (ton) until the next phase switching. During this period, output circuit is turned on.
If the active drive time of each phase is assumed to ‘to’, the following relation can be established:
to = toff + ton
Fixed
constant
Rotation speed
proportional constant
toff = 0.69 C2R2 ........................................1
. From this relation, it can be observed that the ‘to’ and ‘ton’ are in proportional relation with each other, and that the ‘ton/to’
equals the ‘on’ time duty. As a result, a certain rotation speed can be fixed despite the fact that rotation speed exclusively
. depends on each motor.
At the start, the ‘ton’ value becomes longer while the ‘toff’ value remains unchanged. This means that the ‘toff/to’ duty becomes
small enough compared to normal rotation mode. Therefore, the same start torque as that of the full speed rotation can be
obtained because the ‘on’ operation time duty increases. This enables the motor to start at a very low speed.
.(2) Supply voltage (VIN pin)
The LB1860 has the internal parallel regulator which supplies power to the Hall amplifier circuit and the control block.
Therefore, the driver ICs are not affected by power source fluctuations and kickbacks from the motor. They maintain the stable
operations even if noise signals such as surge are generated.
. Set the resistance R1 between VCC and VIN so that the ICC current of 6 mA to 50 mA can flow onto the VIN pin within the
supply voltage range of a fan motor.
. VIN is 6.7 V typ at ICC = 7 mA.
. The current flowing into VIN is calculated using the equation shown below.
.. ICC =
VCC – VIN
R1
............................ 2
Consideration given to surge voltage
The maximum allowable current at VIN pin is 200 mA. Therefore, the pin is designed to withstand abnormal positive voltage of:
Vsurge = VIN + R1 200 mA ............................................ 3
.(3) Hall input pin voltage (Pins IN–, IN+)
Set the voltage levels of the input pin for the Hall element output and the Hall element output voltage to within the range of
. 0 V to VIN – 1.5 V.
The gain between the hall input pin and the output pin is 100 dB or greater. The offset voltage of the hall input amp is 7 mV,
therefore, the hall element output must be set with the offset voltage (7 mV) considered.
(4) Output transistor (Pins OUT1, OUT2)
. Output current
IO = 1.5 A max
. Output saturation voltage
VO sat = 1.15 V/1.0 A typ
. Output limiting voltage
VOLM = 57 V typ (LB1860, 1860M)
VOLM = 32 V typ (LB1861,1861M)
. Since the LB1860 series have a protect zener diode between collector and base, the kickback voltage induced by the coil is cut
at VOLM = 57 V (32 V). When external capacitors are connected between OUT and GND, the capacitance should not exceed
10 μF.
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