LV8121V SANYO [Sanyo Semicon Device], LV8121V Datasheet - Page 12

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

8. Hall Input Signal
9. FG Output
10. HB Pin
11. Constraint Protection Circuit
The input amplitude of 100mVp-p or more (differential) is desirable in the Hall inputs. The closer the input
wave-form is to a square wave, the required input amplitude is lower. Inversely, the closer the input wave-form is to a
triangular wave, the higher input amplitude is required. Also, note that the input DC voltage must be set within the
common mode input voltage range.
For the Hall IC application, one side (either the + or – side) of the Hall inputs must be fixed at a voltage within the
common mode input voltage range that applies when the Hall-effect sensors are used, and the input voltage range for
the other side becomes 0V to VREG.
If noise on the Hall signals is a problem, that noise must be excluded by inserting capacitor between the Hall inputs as
close as possible to these pins.
When the Hall inputs for all three phases are in the same state, all the outputs (the both upper side and lower side
N-channel power FET) are turned off.
The FG pin is the pulse output that has the same frequency as Hall input IN1 (one Hall-effect sensor FG output).
The HB pin is the 5V constant voltage output that combines the switch function. This pin is connected to the base of
external NPN transistor that supplies the bias of the Hall-effect sensors. If the HB output is turned off, this external
NPN transistor is too turned off, and the bias of the Hall-effect sensors is cut (Hall bias switch).
The HB output is turned off and is made pull-down by a 100kΩ internal resistor when the S/S pin is the stop mode.
Therefore, the bias of the Hall-effect sensors can be cut when the S/S pin is the stop mode.
In case the LIM pin is not used (LIM = GND), if the CTL voltage falls below 0.7V, the HB output is turned off, and
the bias of the Hall-effect sensors is cut.
In case the minimum output duty is determined by the LIM pin, even if the CTL voltage falls below 0.7V, the HB
output is not turned off.
If the HB pin is not used, keep open.
The constraint protection circuit operates to turn the motor drive (the upper side N-channel power FET) on or off
repeatedly in the motor constrained state. Therefore, the IC and the motor are protected. The drive on/off time can be
set by adjusting the oscillation frequency of the CSD pin with external capacitor. When a capacitor C [μF] is
connected between the CSD pin and GND1, the drive on/off time is calculated as follows.
When a 0.047μF capacitor is connected, this protection function will iterate an on/off period in which drive is on for
about 0.39sec and off for about 5.8sec.
By the variance of the IC, “8.21” of the above formula has varied from 5.41 to 11.01.
If the switching from L to H of the Hall input IN1 (the rising edge on the FG output) is not caused during the drive on
time, this protection function turns the motor drive off, and returns the motor drive on after the drive off time.
If the drive on time to be set is too short, this protection function operates at a normal motor start-up, and the motor
may not speed up since this protection function iterates an on/off period. Also, if the motor speed is too low, this
protection function operates when one cycle of the Hall input IN1 is longer than the drive on time. The drive on time
must be set to a sufficient time so that this protection function does not operate except the motor constrained state.
The oscillation waveform of the CSD pin is used for some circuits in addition to the constraint protection circuit.
Therefore, it is desirable to oscillate the CSD pin even if the constraint protection function is unnecessary.
The CSD pin combines the function as the initial reset pin. The time that the CSD voltage is charged to about 1.25V is
determined as the initial reset. At the initial reset, all the outputs (the both upper side and lower side N-channel power
FET) are turned off.
If the constraint protection function is not used, the oscillation of the CSD pin must be stopped by connecting a 220kΩ
resistor and a 0.01μF capacitor in parallel between the CSD pin and GND1. However, when the oscillation of the CSD
pin is stopped, note that some functions do not operate in the following cases.
• If the motor does not rotate at the motor start-up because the motor is constrained, the upper side N-channel power
• In case the LIM pin is not used (LIM = GND), even if the CTL voltage falls below 0.7V, the HB output is not turned
FET may be switched by the current limiter. But, the synchronous rectification does not operate when the oscillation
of the CSD pin is stopped.
off when the oscillation of the CSD pin is stopped.
TCSD1 (drive on time) = 8.21 × C
TCSD2 (drive off time) = TCSD1 × 15
Continued on next page.
LV8121V
No.A2135-12/14