MAX14870 Datasheet, PDF (12/15 Pages) Maxim Integrated Products – Full-Bridge DC Motor Drivers

MAX14870/MAX14872
Compact 4.5V to 36V
Full-Bridge DC Motor Drivers
M1
COM
GND
GN^EP D
GND
GND
GND
GND
COM
M2
To SNS
R_SENSE
Figure 4. Layout Example for Accurate Current Sensing
Current Regulation
The MAX14870/MAX14872 features internal current
regulation to limit the startup current. Regulation is set
when the motor current (IM) exceeds the current limit
defined by the sense resistor (RSENSE):
IM_MAX = 0.1V/RSENSE
When the motor current exceeds the maximum threshold,
the H-bridge drive is reversed for fast decay for a fixed
time (tOFF = 15μs). The H-bridge is turned back to normal
operation after tOFF.
Fast Decay Mode
When the motor current exceeds the set threshold, the
H-bridge polarity is reversed during the 15μs (typ) t_OFF
period. This results in faster motor current decay since
–VDD is applied across the motor’s terminals. The motor
current decrease is first order with an L/R time constant
and proportional to (VDD + VEMF).
Note that if tOFF is larger than the motor’s L/R electrical
time constant, the motor current can reverse direction,
causing the motor to not start.
During fast decay, the motor’s inductive current recircu-
lates through the external VDD supply, which charges up
the VDD bypass capacitor. Therefore, the voltage seen
across RSENSE is negative during the tOFF delay.
Applications Information
Layout Considerations
Connect duplicate pins (COM pins and VDD pins) togeth-
er with low-resistance traces. See the Current Sensing
section for further layout recommendations.
Power Considerations
The MAX14870/MAX14872 driver can generate more
power than the package for the device can safely dissi-
pate. Total power dissipation for the device is calculated
using the following equation:
PTOTAL = PDRIVER + PSW + PD
The power dissipated inside of the driver is calculated as:
P_DRIVER = IM² x R_ON
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