MAX14870 Datasheet, PDF (13/15 Pages) Maxim Integrated Products – Full-Bridge DC Motor Drivers

MAX14870/MAX14872
Compact 4.5V to 36V
Full-Bridge DC Motor Drivers
where IM is the motor current and RON is the on-resis-
tance of the high and low-side FETs.
PSW is the power generated by the driver during the rise/
fall times in switching and includes both arms of the bridge.
Calculate PSW using the following equation:
PSW = IM x 2 x V_DS
= IM x 2 x (1/2 x V_DD x fSW x tR)
where IM is the motor current, tR is the 200ns (typ) rise
or fall time of the driver output, and fSW is the switching
frequency.
The internal diodes dissipate power during switching, as
well. Calculate the power dissipated in the diodes as:
PD = IM x 2 x V_BF x tDEAD x fSW
Operation Without Current Regulation
To operate the MAX14870/MAX14872 without internal or
external current regulation, connect SNS directly to GND.
No sense resistor is required for this configuration.
Operation with External Current Regulation
The motor current can be controlled by external PWM
regulation using sense resistor feedback in a control loop.
To disable the internal current regulation circuitry of the
MAX14870/MAX14872 and use external regulation, con-
nect SNS directly to ground.
Note that, if fast decay control is used, the COM voltage
pulses negatively when the H-bridge direction is inverted.
Use of external capacitors
Maxim does not recommend using external capacitors
across the motor terminals. Added capacitance between
H-bridge outputs increases the power dissipated in the
H-bridge by:
PD = VDD² x C x fSW
where C is the capacitance across M1/M2 and fSW is
the M1/M2 switching frequency. This power is dissipated
without good reason.
3.3V
IRQ
GPO
PWM
µC
ADC
3.3V
FAULT
DIR⁺
PWM⁺
EN
9V
M
VDD
M1
VUVLO
VDD
DRIVER
M2
MAX14870
MAX14872
VDD
DRIVER
CURRENT
REGULATION
SNS
A
COM
RSENSE
GND
+ _{These pin names are for the MAX14870. On the MAX14872, these are the FWD and REV inputs.}
Figure 5. Operation with External Current Regulation
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