MP6551

– 14V, 5A, H-BRIDGE MOTOR DRIVER

MP6551 Rev. 1.0

MonolithicPower.com

10

7/7/2021

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© 2021 MPS. All Rights Reserved.

OPERATION

The MP6551 is an H-bridge motor driver that

integrates four N-channel power MOSFETs. It

can achieve 5A of peak output current (IOUT)

across a 2.5V to 14V input voltage (VIN) range,

and is designed to drive brushed DC motors,

solenoids, and other loads.

Input Logic

Each

of

the

MP655

1’s half H-bridges is

controlled independently via the IN1, IN2, EN1,

and EN2 input pins. Table 1 shows the control

logic for each input pin.

Table 1: Input Pin Control Logic

INx

ENx

OUTx

X

0

Z

0

1

L

1

1

H

Sleep Mode

Pull the EN1 and EN2 pins low to enable sleep

mode. In sleep mode, all internal circuitry

(including the gate driver charge pump) is

disabled, and the outputs are turned off. If

either EN1 or EN2 is enabled again, then the

device resumes normal operation. There is a

short delay time (tWAKE) before the output(s) are

enabled again.

Slew Rate (SR) Control

The MP6551 has a slew rate (SR) control pin.

Use a resistor to connect the SR pin to GND to

adjust the slew rate (output rise/fall time). This

feature can reduce electromagnetic interference

(EMI) caused by output transitions.

The

rise/fall

time

is

proportional

to

the

resistance used. Short SR to GND to generate

a fast rise/fall time (about 100ns). A

3MΩ

resistor generates a rise/fall time of about 3µs.

Fault Indication

The MP6551

’s fault indication (nFAULT) pin is

an open-drain output that requires an external

pull-up resistor. The nFAULT pin indicates if a

fault has occurred. If an over-current (OC) or

over-temperature (OT) fault occurs, nFAULT is

pulled low. Once the fault condition is removed,

nFAULT is pulled high via the pull-up resistor.

Current Measurement Outputs

The internal current-sensing circuitry senses

the current flowing into each output. The CM1

and CM2 pins source or sink a current

proportional to the current flowing into each of

the half H-bridges

’ low-side MOSFETs (LS-

FETs). The current flowing through the LS-FET

is sensed in both the forward and reverse

directions.

To convert this current into a voltage (e.g. to

input to an analog-to-digital converter [ADC]), a

termination resistor (RREF) is required to create

a reference voltage (VREF). If no current is

flowing, then the resultant output is equal to

VREF. If the current is flowing, then the voltage is

above or below VREF. (VOUT_SENSE) can be

calculated with Equation (1):

VOUT_SENSE = VREF + (RREF x ILOAD) / 10,000 (1)

To terminate the outputs while using an ADC

with inputs that are ratiometric to its supply

voltage, connect two equal-value resistors to

the ADC supply and GND. The resulting ADC

code is half-scale at zero current.

Figure 2 shows the current measurement circuit.

OUTx

GND

x1

x10,000

x1

CMx

VREF

RREF

VOUT_SENSE

IOUT_SENSE

ILOAD

IOUT_SENSE = ILOAD / 10,000

VOUT_SENSE = VREF + (IOUT_SENSE x RREF)

VOUT_SENSE = VREF + (ILOAD x RREF) / 10,000

Matched

Figure 2: Current Measurement Circuit

If only the total current needs to be measured

(e.g. the current of a full H-bridge driver), then

the CM1 and CM2 pins can be connected to

measure the sum of the two half H-bridge

currents.

Over-Current Protection (OCP)

Over-current protection (OCP) protects the

device from damage due to excessive current

at the outputs. If the current through a MOSFET

exceeds the current limit threshold, then the

foldback current limit function limits IOUT to a

safe level and nFAULT goes low.