lb11695m Sanyo Semiconductor Corporation, lb11695m Datasheet - Page 14

• Manufacturer Part Number: lb11695m
• Description: 3-phase Brushless Pre-driver, Direct Pwm Drive
• Manufacturer: Sanyo Semiconductor Corporation

LB11695M Functional Description
1. Output Drive Circuit
2. Current Limiter Circuit
3. Power Saving Circuit
4. Handling Different Power Supply Types
5. Notes on the PWM Frequency
The LB11695M adopts direct PWM drive to minimize power loss in the outputs. The output transistors are always
saturated when on, and the motor drive power is adjusted by changing the on duty of the output. The output PWM
switching is performed on the UH, VH, and WH outputs. Since the UL to WL and UH to WH outputs have the same
output form, applications can select either low side PWM or high side PWM drive by changing the way the external
output transistors are connected. Since the reverse recovery time of the diodes connected to the non-PWM side of the
outputs is a problem, these devices must be selected with care. (This is because through currents will flow at the
instant the PWM side transistors turn on if diodes with a short reverse recovery time are not used.)
The outputs UL through WL and UH through WH are held in the high-impedance state when the IC is stopped or the
supply voltage is too low (below the allowable operating voltage level). Consequently, it is necessary to take
necessary measures (e.g., adding a pull-down resistor) to prevent the external circuit from malfunctioning due to leak
current.
The current limiter circuit limits the output current peak value to a level determined by the equation I = V RF /Rf
(V RF = 0.25V typical, Rf: current detection resistor). This circuit
suppresses the output current by reducing the output on duty.
The current limiter circuit includes an internal filter circuit to
prevent incorrect current limiter circuit operation due to detecting
the output diode reverse recovery current due to PWM operation.
Although there should be no problems with the internal filter circuit
in normal applications, applications should add an external filter circuit (such as an RC low-pass filter) if incorrect
operation occurs (if the diode reverse recovery current flows for longer than 1µs).
This IC goes to a low-power mode (power saving state) when set to the
stop state with the S/S pin. In the power saving state, the bias currents in
most of the circuits are cut off. However, the 5V regulator output
(V REG ) is still provided in the power saving state. If it is also necessary
to cut the Hall device bias current, this function can be provided by an
application that, for example, connects the Hall devices to 5V through
PNP transistors.
When this IC is operated from an externally supplied 5V power supply (4.5 to 5.5V), short the V CC pin to the V REG
pin and connect them to the external power supply. When this IC is operated from an externally supplied 12V power
supply (8 to 13.5V), connect the V CC pin to the power supply. (The V REG pin will generate a 5V to function as the
power supply to the control circuit.)
When this IC is operated from on an externally supplied 15V power supply (13.5 to 19V), connect the V15 pin to the
power supply and short between the 12REG and VCC pins. (The 12REG pin will generate a 12V to function as the
V CC power supply.)
The PWM frequency is determined by the capacitor C (F) connected to the PWM pin.
If a 1000pF capacitor is used, the circuit will oscillate at about 22kHz. If the PWM frequency is too low, switching
noise will be audible from the motor, and if it is too high, the output power loss will increase. Thus a frequency in the
range 15 to 50kHz must be used. The capacitor's ground side lead must be placed as close as possible to the IC’s
ground pin to minimize the influence of output noise and other noise sources.
fPWM ≈ 1/(45000 × C)
LB11695M
To the RF pin
To the VREG pin
To the S/S pin
Current detection
resistor
Hall device
No.7948-14/17