LV8121V SANYO [Sanyo Semicon Device], LV8121V Datasheet - Page 11

• Manufacturer Part Number: LV8121V
• Description: For Fan Motor 3-phase Brushless Motor Driver
• Manufacturer: SANYO [Sanyo Semicon Device]

Continued from preceding page.
4. Current Limiter Circuit
5. Reference Oscillator
6. Start/Stop Switching Circuit
7. Forward / Reverse Switching Circuit
In case of limiting the bounce of the power supply voltage, the maximum voltage of
the V CC can be limited according to the following method. The maximum voltage of
the VG is limited by using Zener diode, NPN transistor and some resistors. Normally,
the relation between VG and V CC becomes “VG = V CC + 4.7V”. If V CC rises above
“VG max - 4.7V” when VG is limited to VG max, this relation does not keep.
Because the sufficient gate voltage cannot be applied to the upper side N-channel
power FET when this relation does not keep, this IC includes the protective function
that turns off the upper side N-channel power FET.
Accordingly, if V CC rises above “VG max - 4.7V” when VG is limited to VG max, the upper side N-channel power
FET is turned off, and the V CC bounce caused by dropping the CTL voltage can be limited to
“V CC = VG max - 4.7V”. When the above reference circuit is used, VG is limited to about 36.7V, and V CC is limited
to about 32.0V. But this function does not guarantee that any V CC bounce can be limited. If V CC is steeply bounced
by dropping the CTL voltage, this function may not limit the V CC bounce.
The current limiter circuit limits the output current peak to the value determined by “I = V RF /Rf” (V RF = 0.25V typ.,
Rf: current detection resistor). When the current limiter is operating, the upper side N-channel power FET is switched,
and the output current is suppressed by reducing the output duty.
Connect a 56pF capacitor between CT and GND1, and a 11kΩ resistor between RT and CT. Then, the reference
oscillation frequency becomes about 2.1MHz. The reference oscillation frequency functions as a reference clock for
the internal logic circuit. The charge pump circuit boosts the voltage using a frequency that is 1/32 of the reference
oscillation frequency.
When the S/S pin is set to the low level, start/stop switching circuit is the start mode. Inversely, when the S/S pin is set
to the high level or open, start/stop switching circuit is the stop mode. This IC goes into a power saving state that
reduces the supply current at the stop mode. In the power saving state, the bias current is removed from most of the
circuits in the IC.
The operating circuits in the power saving state are limited to the start/stop switching circuit and the 5V constant
voltage output. The other circuits do not operate. Both upper side and lower side N-channel power FET are turned off
in the power saving state.
If a minus voltage is applied to the S/S pin, this pin current must be limited within 2mA by inserting the resistor of
about 200Ω.
The motor rotation direction can be switched by using the F/R pin. However, the following notes must be observed if
the F/R pin is switched while the motor is rotating.
• This IC is designed to avoid the through current when the direction is switched. However, the bounce of the V CC
• If the motor current after the direction switching exceeds the current limiter value, the upper side N-channel power
If a minus voltage is applied to the F/R pin, this pin current must be limited within 2mA by inserting the resistor of
about 200Ω.
voltage (due to the motor current that flows instantly on the power supply side) may be caused during the direction
switching. If this bounce is a problem, the capacitance inserted between V CC and GND must be increased.
FET will be turned off, but the lower side N-channel power FET will be the short brake condition. On the short
brake condition, the current determined by the motor back EMF voltage and the coil resistance will flow. Because
the current limiter circuit of this IC cannot limit this current, applications must be designed so that this current does
not exceed the maximum rating (3.5A). When the motor speed is higher, the direction switching is dangerous.
LV8121V
160kΩ
33kΩ
5.1kΩ
5.6V
Zener
No.A2135-11/14
To VG