Technical Note

11/16

BD6220, BD6221, BD6222, BD6225, BD6226, BD6227

www.rohm.com

2009.08 - Rev.C

○

c

2009 ROHM Co., Ltd. All rights reserved.

i) j) VREF control mode

The built-in VREF-switching on duty conversion circuit provides switching duty corresponding to the voltage of the

VREF pin and the VCC voltage. The function offers the same level of control as the high voltage output setting

function in previous models. The on duty is shown by the following equation.

DUTY ≈ VREF [V] / VCC [V]

For example, if VCC voltage is 12V and VREF pin voltage is 9V, the switching on duty is about 75 percent. However,

please note that the switching on duty might be limited by the range of VREF pin voltage (Refer to the operating

conditions, shown on page 2). The PWM carrier frequency in this mode is 25kHz (nominal), and the switching

operation is the same as it is the PWM control modes. When operating in this mode, do not input the PWM signal to

the FIN and RIN pins. In addition, establish a current path for the recovery current from the motor, by connecting a

bypass capacitor (10µF or more is recommended) between VCC and ground.

Fig.42 VREF control operation (timing chart)

2) Cross-conduction protection circuit

In the full bridge output stage, when the upper and lower transistors are turned on at the same time, and this condition

exists during the period of transition from high to low, or low to high, a rush current flows from the power supply to

ground, resulting in a loss. This circuit protects against the rush current by providing a dead time (about 400ns,

nominal) at the transition.

3) Output protection circuits

a) Under voltage lock out (UVLO) circuit

To secure the lowest power supply voltage necessary to operate the controller, and to prevent under voltage

malfunctions, a UVLO circuit has been built into this driver. When the power supply voltage falls to 5.0V (nominal) or

below, the controller forces all driver outputs to high impedance. When the voltage rises to 5.5V (nominal) or above,

the UVLO circuit ends the lockout operation and returns the chip to normal operation.

b) Over voltage protection (OVP) circuit

When the power supply voltage exceeds 30V (nominal), the controller forces all driver outputs to high impedance.

The OVP circuit is released and its operation ends when the voltage drops back to 25V (nominal) or below. This

protection circuit does not work in the stand-by mode. Also, note that this circuit is supplementary, and thus if it is

asserted, the absolute maximum rating will have been exceeded. Therefore, do not continue to use the IC after this

circuit is activated, and do not operate the IC in an environment where activation of the circuit is assumed.

VCC

VREF

FIN

RIN

OUT1

OUT2

0