Data Sheet

TB67S279FTG, TB67S289FTG, TB67S249FTG Application Note
2018-03-07
15 / 33
Preliminary
8.6.4. FLIM (AGC frequency limit) function
FLIM pin sets the bottom frequency (frequency limit) for AGC to be active. Since AGC uses an
induced voltage in operating, some motors have unstable AGC operation when the motor rotation
is very slow. Also, the motor’s own resonance frequency influences on the AGC operation. Thereby,
the lower frequency limit for AGC activation is necessary to avoid above and can be set by FLIM
pin.
FLIM pin is a 4 stated logic input. Built-in digital filter of 0.625 μs (±20%) is adopted to FLIM pin.
Mode FLIM Function
1 Connected to VCC
Frequency limit: ON, AGC is invalid when fCLK is less than 675 Hz
2
Pulled up to VCC with100
kΩ-resistor
Frequency limit: ON, AGC is invalid when fCLK is less than 450 Hz
3
Pulled down to GND with100
kΩ-resistor
Frequency limit: ON, AGC is invalid when fCLK is less than 225 Hz
4 Connected to GND
Frequency limit: OFF
When connected to GND, the operation is not limited by the limiter circuit of the IC. The induced
voltage of the motor, which is used in AGC, is generated by the rotation of the motor. Therefore,
the frequency threshold for AGC activation is unique to the motor.
The frequency threshold for AGC activation shown in the above table is the case of full step
resolution. When using other step resolutions (micro step resolution), the thresholds are different.
In micro stepping, the thresholds are roughly equivalent to conversion of the full step resolution.
Please refer to the table below.
FLIM
Full step
resolution
Half (a) step
resolution
Half (b) step
resolution
Quarter step
resolution
1/8 step
resolution
1/16 step
resolution
1/32 step
resolution
Connected to VCC
675 Hz 1.35 kHz 1.35 kHz 2.7 kHz 5.4 kHz 10.8 kHz 21.6 kHz
Pulled up to VCC with100
kΩ-resistor
450 Hz 900 Hz 900 Hz 1.8 kHz 3.6 kHz 7.2 kHz 14.4 kHz
Pulled down to GND
with100 kΩ-resistor
225 Hz 450 Hz 450 Hz 900 Hz 1.8 kHz 3.6 kHz
7.2 kHz
Connected to GND
Frequency limit: OFF
8.6.5. LTH (AGC detection threshold) function
LTH pin sets AGC detection threshold.
Torque detection sensitivity can be set by changing the connected resistor value. When lowering
the resistor value, the detection sensitivity increases but the constant current value may become
unstable for some motors. Therefore, caution should be exercised.
The resistor can be lowered to about 10 k Ω. Connect a 100 kΩ-resistor in the normal usage.
LTH Function
Pulled down with100
kΩ-resistor
Standard configuration for AGC detection threshold
Pulled down with10
kΩ-resistor
Upper limit configuration for AGC detection threshold