Detailed Description
The MAX14870/MAX14872 DC brushed motor drivers
provide a low-power and flexible solution for driving and
controlling brushed motors with voltages between 4.5V
and 36V. Peak motor currents of up to 2.5A ensure large
motor torque that is controllable by an external PWM
signal and/or by autonomous internal current regulation.
The MAX14870 has PWM and direction-control inputs,
while the MAX14872 has forward and reverse inputs for
direction control. See the MAX14870 Function Table and
MAX14872 Function Table.
Charge-pump-less design requires minimal external
components and low supply current.
Integrated current regulation allows limiting peak start-
up motor currents. Shoot-through protection with a
140ns (typ) dead time ensures low operating current.
Internal free-wheeling diodes absorb inductive motor cur-
rents. The FAULT output signals thermal overload and
overcurrents.
Overcurrent Protection
The MAX14870/MAX14872 are protected against shorts
on M1/M2 to any voltage between V
DD
and GND, includ-
ing shorts to GND, V
DD
, and between M1 and M2 via
overcurrent limiting. When a current above 6A (typ)
flows through M1 or M2 for longer than 1µs, an overcur-
rent condition is detected and the H-bridge drivers are
automatically disabled and the FAULT output asserts.
If the overcurrent condition continues for longer than the
overcurrent autoretry timeout (2ms (typ)) the MAX14870/
MAX14872 enters autoretry mode. In autoretry mode,
the M1 and M2 outputs are re-enabled for 1µs (typ) and
FAULT goes high-impedance. The drivers are disabled
again and FAULT is re-asserted if the overcurrent condi-
tion persists.
PWM Control (MAX14870 Only)
The PWM input is used for motor speed/torque control.
Increasing or decreasing the duty cycle at PWM sets the
effective (average) voltage across the motor terminals
and allows first-order speed control.
When PWM is logic-high, the motor is driven in the direc-
tion defined by DIR. When PWM is logic-low, the bridge
is in brake mode. In brake mode, the motor current
continues flowing and recirculates through the low-side
transistors of the H-bridge driver, due to its inductive
impedance and back EMF.
FWD/REV Control (MAX14872 only)
The FWD input is used to drive the motor forward/turn a
relay on. The REV input reverses the M1 and M2 polarity,
to drive the motor in reverse/turn a relay off.
FWD/REV control can be optionally used to implement
either bipolar motor control (with both M1 and M2 switch-
ing) or unipolar control, where only M1 or M2 switches.
Slope Control
The MAX14871 drivers turn-on and turn-off with active
slope-control during the M1/M2 transition times. The
integrated slew rate-limiting reduces EMC (like conducted
and radiated EMI) associated with high di/dt rates.
Thermal Shutdown
The MAX14870/MAX14872 include integrated protection
against thermal overload. When the junction temperature
exceeds 160°C (typ), the H-bridge is three-stated, M1 and
M2 are disabled, and FAULT is asserted.
If the motor was spinning before thermal shutdown
occurred, the motor’s inductance will push current through
the internal M1 and M2 diodes, forcing the motor into fast
decay, with a voltage across its terminals of V
DD
.
M1 and M2 are automatically reenabled when the
junction temperature falls to 150°C (typ).
Current Sensing
Connect a sense resistor (R
SENSE
) between COM
and GND to monitor the motor current during operation.
Select R
SENSE
such that the voltage at COM created by
motor current flowing through the sense resistor is limited
to within 250mV relative to GND (-250mV ≤ V
COM
≤
+250mV).
Minimize series trace resistance from R
SENSE
to GND
to minimize voltage sense errors due to parasitic trace
interconnect resistance. Use a star ground connection
between the MAX14870/MAX14872 GND pins and the
GND-side of R
SENSE
. Connect the voltage sense close
to the R
SENSE
resistor and/or use differential voltage
sensing. See Figure 4.
MAX14870/MAX14872 Compact 4.5V to 36V
Full-Bridge DC Motor Drivers
www.maximintegrated.com
Maxim Integrated
│
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