Reference voltage. In the Typical Application shown,
resistors R 1 and R 2 set the reference voltage as:
V REF = (V DD x R 2 )/(R 1 + R 2 )
The trimming of R 2 allows for the resistor tolerances
and REF input current. The sum of R 1 +R 2 should be less
than 50 kΩ to minimize the effect of I REF . Raising V REF
above 2 V by activating Q1 causes the sleep mode.
Minimum output current. The Series SLA7060M uses
fixed off-time PWM current control. Due to internal logic
and switching delays, the actual load current peak will be
slightly higher than the calculated I TRIP value (especially
for low-inductance loads). These delays, plus the mini-
mum recommended V REF , limit the minimum value the
current-control circuitry can regulate. An application with
this device should maintain continuous PWM control in
order to obtain optimum torque out of the motor. The
boundary of the load current (I O(min) ) between continuous
and discontinuous operation is:
I O(min) = [(V M + V SD )/R m ] x [(1/e t off /[R m x L m ] ) - 1]
where V M = load supply voltage
V F = body diode forward voltage
R m = motor winding resistance
t off = PWM off time
L m = motor winding inductance
To produce zero current in a motor, the REF input
should be pulled above 2 V, turning off all drivers.
