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:

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:

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:

where C is the capacitance across M1/M2 and fSW is

the M1/M2 switching frequency. This power is dissipated

without good reason.

Figure 5. Operation with External Current Regulation

DRIVER

VDD

SNS

MAX14870

MAX14872

GND

COM

M1

M2

EN

FAULT

DRIVER

CURRENT

REGULATION

µ

C

IRQ

PWM

GPO

ADC

9V

3.3V

3.3V

M

A

MAX14870/MAX14872

Compact 4.5V to 36V

Full-Bridge DC Motor Drivers

www.maximintegrated.com

Maxim Integrated │ 13