MAX14871_14 Datasheet, PDF (13/15 Pages) Maxim Integrated Products – 4.5V to 36V Full-Bridge DC Motor Driver

MAX14871
4.5V to 36V Full-Bridge DC Motor Driver
The power dissipated inside of the driver is calculated as:
P_DRIVER = IM_LOAD² x R_ON
where IM_LOAD is the motor current and RON is the on-
resistance 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_LOAD x 2 x V_DS
= IM_LOAD x 2 x (1/2 x V_DD x fSW x tR)
where IM_LOAD 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_LOAD x 2 x V_BF x tDEAD x fSW
Operation Without Internal Current Regulation
To operate the MAX14871 without internal or external
current regulation, connect SNS directly to GND. No
sense resistor is required for this configuration. See
Figure 4.
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
MAX14871 and use external regulation, connect SNS
directly to ground. See Figure 5.
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.
Note that conducted EMI on the VDD lines is also
worsened due to the high-capacitive current spikes.
3.3V
IRQ
GPO
PWM
µC
ADC
9V
M
3.3V
FAULT
DIR
PWM
EN
VDD
M1
VDD
DRIVER
TCOFF
MODE
VREF
CURRENT
REGULATION
SNS
A
M2
MAX14871
VDD
DRIVER
COM
RSENSE
GND
Figure 5. Operation with External Current Regulation
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