Data Sheet

TB67S279FTG, TB67S289FTG, TB67S249FTG Application Note
2018-03-07
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Preliminary
8.6.2. CLIM (AGC bottom current limit) function
AGC judges the required torque value and decreases the current value from the constant current,
which is set by VREF.
In order to avoid stalls including motor-system stalls, this constant current value should have
enough margins.
Since actual required current value for motor driving is generally lower than this set current value,
the motor driving current is reduced to the minimum required value (torque value) when AGC is
enabled.
However, in the case that the load torque is very small, the set current itself becomes very small.
And when the required torque becomes high due to the load fluctuates, its current difference may
be very big.
In this case, following problems generate; it takes longer time to increase the current to the
required level, and delay of torque following (depending on motor characteristics) occurs stalling.
As a counter measure for above problems, CLIM (Current limit) function prevents the current
value from falling too much compared to the set constant current value.
CLIM0 and CLIM1 pins can set the lower current limit in 8 levels. CLIM0 is a 2 stated logic input,
and CLIM1 is a 4 stated logic input.
Usually, it is effective to start the evaluation from the ‘Iout × 80%’ condition and lower the current
limit to determine the margin limit that allows the system operation. This evaluation can be
performed by using CLIM0 and CLIM1 setting combinations.
Even when operating the IC with ‘Iout × 80%’ condition, the power consumption can be saved
greatly because it is proportional to the square of Iout.
Built-in digital filter of 0.625 μs (±20%) is adopted to CLIM0 and CLIM1 pins.
This function is disabled when AGC is not used.
CLIM0 CLIM1 Function
High
Connected to VCC
AGC bottom current limit: Iout × 80%
Pulled up to VCC with100
kΩ-resistor
AGC bottom current limit: Iout × 75%
Pulled down to GND with100
kΩ-resistor
AGC bottom current limit: Iout × 70%
Connected to GND
AGC bottom current limit: Iout × 65%
Low
Connected to VCC
AGC bottom current limit: Iout × 60%
Pulled up to VCC with100
kΩ-resistor
AGC bottom current limit: Iout × 55%
Pulled down to GND with100
kΩ-resistor
AGC bottom current limit: Iout × 50%
Connected to GND
AGC bottom current limit: Iout × 45%