3951
FULL-BRIDGE
PWM MOTOR DRIVER
V
BB
between the duty cycle on the phase input and the aver-
age voltage applied to the motor is more linear than in the
case of ENABLE PWM control (which produces a discon-
tinuous current at low current levels). See also, “DC Motor
Applications” below.
MISCELLANEOUS INFORMATION
An internally generated dead time prevents crossover
currents that can occur when switching phase or braking.
DRIVE CURRENT
RECIRCULATION
R
S
Thermal protection circuitry turns off all drivers should
the junction temperature reach 165°C (typical). This is
intended only to protect the device from failures due to
excessive junction temperatures and should not imply that
output short circuits are permitted. The hysteresis of the
thermal shutdown circuit is approximately 15°C.
Dwg. EP-006-10
Figure 3 — Load-Current Paths
ENABLE Pulse-Width Modulation
Toggling the ENABLE input turns on and off the
selected source and sink drivers; the load inductance
causes the current to flow from ground to the load supply
via the ground clamp and flyback diodes (four-quadrant
operation or fast decay). See figure 3. When the device is
enabled, the internal current-control circuitry will be active
and can be used to limit the load current in the normal
internal PWM slow-decay or two-quadrant mode of opera-
tion.
If the internal current-control circuitry is not used; the
VREF terminal should be connected to VCC, the SENSE
terminal should be connected to ground, and the RC
terminal should be left floating (no connection).
An internal under-voltage lockout circuit prevents
simultaneous conduction of the outputs when the device is
powered up or powered down.
ENABLE
APPLICATIONS NOTES
Current Sensing
I
The actual peak load current (IOUTP) will be greater
than the calculated value of ITRIP due to delays in the turn
off of the drivers. The amount of overshoot can be ap-
proximated as
TRIP
LOAD
CURRENT
(VBB – ((ITRIP • RLOAD) + VBEMF)) • tpd(pwm)
IOUTP
≈
LLOAD
Dwg. WP-015-4
Figure 4 — ENABLE PWM Load-Current Waveform
PHASE Pulse-Width Modulation
where VBB is the load/motor supply voltage, VBEMF is the
back-EMF voltage of the load, RLOAD and LLOAD are the
resistance and inductance of the load respectively, and
tpd(pwm) is the propagation delay as specified in the electrical
characteristics table.
Toggling the PHASE terminal determines/controls
which sink/source pair is enabled, producing a load current
that varies with the duty cycle and remains continuous at
all times. This can have added benefits in bidirectional
brush dc servo motor applications as the transfer function
The reference terminal has an equivalent input resis-
tance of 50 kΩ ±30%. This should be taken into account
when determining the impedance of the external circuit
that sets the reference voltage value.
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7
SANKEN [ SANKEN ELECTRIC ]
