參數(shù)資料
型號: LB1976
廠商: Sanyo Electric Co.,Ltd.
英文描述: DC Fan Motor Driver
中文描述: 直流風(fēng)扇馬達(dá)驅(qū)動器
文件頁數(shù): 9/12頁
文件大?。?/td> 91K
代理商: LB1976
IC Description
Direct PWM Drive
This IC (LB1976) employs the direct PWM drive principle. Motor rotation speed is controlled by varying the output
duty cycle according to an analog voltage input (V
CTL
). This eliminates the need to alter the motor power supply
voltage. Compared to previous ICs using the PAM principle (such as the Sanyo LB1690), this allows simplification of
the power supply circuitry. The V
CTL
input can be directly supplied by a microcontroller, motor speed can, therefore, be
controlled directly from the microcontroller.
For PWM, the source-side output transistors are switched on and off so that the ON duty tracks the V
CTL
input. The
output duty cycle can be controlled over the range of 0% to 100% by the V
CTL
input.
PWM Frequency
The PWM oscillator frequency f
PWM
[Hz] is set by the capacitance C [pF] connected between the OSC pin and GND.
The following equation applies:
f
PWM
1 / (1.97
×
C)
×
10
8
Because output transistor on/off switching is subject to a delay, setting the PWM frequency to a very high value will
cause the delay to become noticeable. The PWM frequency therefore should normally be kept below 40 kHz (typ.),
which is achieved with a capacitance C of 1300 pF or higher. For reference, the source-side output transistor switching
delay time is about 2 μs for ON and about 4 μs for OFF.
Output Diodes
Because the PWM switching operation is carried out by the source-side output transistors, Schottky barrier diodes must
be connected between the OUT pins and GND (OUT1 to OUT3). Use diodes with an average forward current rating in
the range of 1.0 to 2.0 A, in accordance with the motor type and current limiting requirements.
If no Schottky barrier diodes are connected externally, or if Schottky barrier diodes with high forward voltage (V
F
) are
used, the internal parasitic diode between OUT and GND becomes active. When this happens, the output logic circuit
may malfunction, resulting in feedthrough current in the output which can destroy the output transistors. To prevent this
possibility, Schottky barrier diodes must be used and dimensioned properly.
The larger the V
F
of the externally connected Schottky barrier diodes, or the hotter the IC is, the more likely are the
parasitic diodes between OUT and GND to become active and the more likely is malfunction to occur. The V
F
of the
Schottky barrier diodes must be determined so that output malfunction does not occur also when the IC becomes hot. If
malfunction occurs, choose a Schottky barrier diode with lower V
F
.
Protection Circuits
Low voltage protection circuit
When the V
CC
voltage falls below a stipulated level (V
LVSD
), the low voltage protection circuit cuts off the source-side
output transistors to prevent V
CC
related malfunction.
Thermal shutdown circuit (overheat protection circuit)
When the junction temperature rises above a stipulated value (TSD), the thermal shutdown circuit cuts off the source-
side output transistors to prevent IC damage due to overheating. Design the application heat characteristics so that the
protection circuit will not be triggered under normal circumstances.
Current limiter
The current limiter cuts off the source-side output transistors when the output current reaches a preset value (limiter
value). This interrupts the source current and thereby limits the output current peak value. By connecting the
resistance Rf between the RF pin and ground, the output current can be detected as a voltage. When the RF pin voltage
reaches 0.5 V (typ.), the current limiter is activated. It performs on/off control of the source-side output transistors,
thereby limiting the output current to the value determined by 0.5 /Rf.
No. 6088-9/12
LB1976
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參數(shù)描述
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