LB11690 View Datasheet(PDF) - SANYO -> Panasonic

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Description

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LB11690

Pre-Driver IC for Brushless Motor Drive in Electric Bicycles

SANYO -> Panasonic 

LB11690, 11690H

3. PWM Oscillator Circuit

The PWM frequency is determined by the capacitor C (rated in F) connected to the PWM pin.

fPWM ≈ 1/(93000 × C)

When a 270 pF capacitor is used, the frequency will be about 39 kHz. If the PWM frequency is too low, the motor

will generate audible noise at the switching frequency, and if it is too high, the power loss will increase. A frequency

in the range 20 to 50 kHz is desirable. Connect the ground side of this capacitor to a point as close as possible to the

IC ground pin to minimize the influence of output noise.

4. Control Methods

The output duty is determined by comparing the PWM oscillator waveform to the TOC pin voltage. When the TOC

pin voltage is about 1.2 V or lower, the duty will be 0%, and when that voltage is 3.0 V or higher, the duty will be

100%.

Normally, the integrating amplifier is used as a full feedback amplifier (with

the EI– pin and the TOC pin connected directly), and the control voltage is

input to the EI+ pin. (Here, the output duty increases as the EI+ voltage

TOC

Control voltage

increases.) When the EI+ pin is set to the reset operating state by the RES pin,

the EI pin voltage is lowered to a level close to the ground level by an IC

EI–

internal transistor. (This is to discharge the capacitor.) Therefore, do not

connect a low-impedance power supply directly to this pin, but rather input

EI+

the voltage through a resistor. Also, a pull-down resistor must be inserted

between the EI+ pin and ground so that the motor does not operate when the

control voltage is in the open state. If there is noise on the control voltage or if

it is desirable to suppress rapid fluctuations in the control voltage, a noise

rejection capacitor must be inserted between the EI+ pin and ground. The

To the FV pin

TOC

operating voltage range can be expanded by inputting the control voltage to

the EI+ pin through a resistor voltage divider as shown in the figure.

A speed control circuit using the FV pin can be implemented as shown in the

Control voltage EI–

figure to control the motor so that a constant speed is maintained to a certain

EI+

degree despite variations in the load. A resistor of 25 kΩ or larger must be

used between the FV and EI+ pin. The feedback capacitor must be selected so

that the TOC pin voltage is adequately stable at low speeds.

5. Charge Pump Circuit

The charge pump steps up the supply voltage to generate the high side FET gate voltage. The capacitor CP connected

between the CP1 and CP2 pins is used for step up, and charge is stored on the capacitor CB connected between the

VB and VCC pins. The capacitances of CP and CB must have the following relationship.

CB ≥ CP × 4

The CP capacitor is charged and discharged based on the PWM frequency. While increasing the capacitance of the

capacitor C increases current capacity of the VB power supply, if the capacitance is too large, the charge and

discharge operation may be inadequate. Note that the larger the capacitance of the capacitor VB, the more stable the

VB voltage will be. However, if that capacitance is too large, the time before the VB voltage is generated when

power is first applied will increase. While testing and evaluation is required to set the values of the capacitors CP and

CB, use the following table as a reference for the initial values.

When the VCC supply voltage is under 20 V, the VB power supply current capacity falls rapidly causing the VB

voltage to fall. Care is required in application design to assure that this does not become a problem.

VCC voltage

CP

CB

24 V

0.1 µF

1 µF

36 V

6800 pF

0.47 µF

No. 7543-13/19

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