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BD621xxx Series
i) j) VREF control mode
The built-in VREF duty cycle conversion circuit provides a duty cycle 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 duty cycle is calculated by the following equation.
DUTY ≈ VREF [V] / VCC [V]
For example, if VCC voltage is 5V and VREF pin voltage is 3.75V, the duty cycle is about 75 percent. However,
please note that the duty cycle might be limited by the range of the 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 the PWM control modes. When operating in this mode, do not input a 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.
VCC
VREF
0
FIN
RIN
OUT1
OUT2
Fig.35 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 during high to low
or low to high transition, an inrush current flows from the power supply to ground, resulting to a loss. This circuit
eliminates the inrush current by providing a dead time (about 400ns, nominal) during the transition.
3) Output protection circuits
a) Under voltage lock out (UVLO) circuit
To ensure 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 2.3V (nominal) or
below, the controller forces all driver outputs to high impedance. When the voltage rises to 2.5V (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 7.3V (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 6.8V (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.
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TSZ02201-0P2P0B300070-1-2
25.Dec.2012 Rev.002
© 2012 ROHM Co., Ltd. All rights reserved.
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TSZ22111･15･001
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