Datenblatt-Suchmaschine für elektronische Bauteile |
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LB11870 Datenblatt(PDF) 11 Page - ON Semiconductor |
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LB11870 Datenblatt(HTML) 11 Page - ON Semiconductor |
11 / 14 page LB11870 No.7256-11/14 Continued from preceding page. Pin No. Symbol Pin Description Equivalent Circuit 36 VREG Stabilized power supply output (5V output). Insert a capacitor of about 0.1 μF between this pin and ground for stabilization. 40 VCC1 Power supply. Insert a capacitor of at least 10µF between this pin and ground to prevent noise from entering the IC. 2, 4, 5 7, 18 20, 30 31, 41 42, 43 45, 47 48 NC Since these pins are not connected to the IC internally, they can be used for wiring connections. FRAME Connect this pin to ground. Overview of the LB11870 1. Speed Control Circuit This IC adopts a PLL speed control technique and provides stable motor operation with high precision and low jitter. This PLL circuit compares the phase error at the edges of the CLK signal (falling edges) and FG signal (falling edges on the FGIN+ and FGS signals), and the IC uses the detected error to control motor speed. During this control operation, the FG servo frequency will be the same as the CLK frequency. fFG (servo) = fCLK 2. Output Drive Circuit To minimize power loss in the output circuits, this IC adopts a direct PWM drive technique. The output transistors are always saturated when on, and the IC adjusts the motor drive output by changing the output on duty. The low side output transistor is used for the output PWM switching. Both the high and low side output diodes are integrated in the IC. However, if reverse torque control mode is selected for use during deceleration, or if a large output current is used and problems occur (such as incorrect operation or waveform disruption due to low side kickback), a Schottky diode should be inserted between OUT and ground. Also, if it is necessary to reduce IC heating during steady-state (constant speed) operation, it may be effective to insert a Schottky diode between VCC and OUT. (This is effective because the load associated with the regenerative current during PWM switching is born not by the on-chip diode but by the external diode.) 3. Current Limiter Circuit The current limiter circuit limits the peak level of the current to a level determined by I = VRF/Rf (where VRF = 0.5V (typical) and Rf is the value of the current detection resistor). The current limiter operates by reducing the output on duty to suppress the current. The current limiter circuit detects the reverse recovery current of the diode due to PWM operation. To assure that the current limiting function does not malfunction, its operation has a delay of about 2 μs. If the motor coils have a low resistance or a low inductance, current fluctuations at startup (when there is no reactive power in the motor) will be rapid. The delay in this circuit means that at such times the current limiter circuit may operate at a point well above the set current. Designers must take this increase in the current due to the delay into account when setting the current limiter value. 36 VCC |
Ähnliche Teilenummer - LB11870 |
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Ähnliche Beschreibung - LB11870 |
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