MP6631 – 24V, 3A PEAK, THREE-PHASE BLDC MOTOR DRIVER

MP6631 Rev. 1.1

MonolithicPower.com

13

2/21/2023

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Figure 6 shows the curve configuration when

SPD_ZERO = 0.

37.5% 50% 62.5% 75% 87.5% 100%

Input PWM duty

SPD_MIN

D37.5

D50

D62.5

D75

D87.5

SPD_MAX

Speed

Figure 6: Curve Configuration when

SPD_ZERO = 0

Speed Open-/Closed-Loop Control

In closed-loop mode (OPEN_L = 0, CLOSE_H

= 1), the MP6631 internally detects the Hall

signal speed and feedback to the control loop,

then adjusts the output PWM duty in a closed

loop. By doing this, the motor speed follows the

reference exactly.

In open-loop mode (OPEN = 1), the OUTA,

OUTB, and OUTC output duty cycles directly

depend on the PWM input duty.

In mixed mode (OPEN_L = 0, CLOSE_H = 0),

the MP6631 operates in closed-loop mode

when the PWM input duty is below 87.5%, and

operates in open-loop mode when input duty

exceeds 87.5%.

Soft-Start Time

To reduce the input inrush current during start-

up, the MP6631 provides the reference speed

’s

configurable soft-start time (tSS) by setting

register bits TDYN[1:0]. This time can be

configured from 1.3s to 10.4s.

Closed-Loop Integrator Gain

In closed-loop mode, the closed-loop integrator

gain depends on registers KI[7:0] and KP[7:0].

Higher KI and KP values lead to quick loop

response. KI and KP should be adjusted

according to the dynamic response and steady

state operation.

Single- or Triple-Hall Input Mode

The MP6631 supports either a single or triple

Hall-effect sensor. If a single Hall-effect sensor

is employed, the Hall selecting bit must set the

single Hall sensor, and Hall C is used as the

control.

Direction Control

The direction is controlled by the

DIR pin’s

polarity. When DIR is pulled low, the MP6631

operates in forward rotation in the following

sequence: A → B → C → A

…

When DIR is pulled high, the MP6631 operates

in reverse rotation in the following sequence: A

→ C → B → A...

Alignment

After VCC start-up, all MOSFETs remain off

until the fan speed drops below the threshold

speed or for a set time, determined by the

register setting.

In single Hall sensor applications, the MP6631

aligns the rotor in certain positions depending

on the Hall outputs. After the alignment time set

by register TOPS completes, the MP6631

enters pre-startup. This function is only enabled

in single Hall sensor applications.

Pre-Startup Timer

During

pre-startup,

the

MP6631

gradually

increases the output duty cycle with the timer

set by the TPRE[1:0] bits. This provides

sufficient torque for robust start-up and avoids

current overshoot during start-up.

• TPRE[1:0] = 0: Timer period is 2.5ms

• TPRE[1:0] = 1: Timer period is 5ms

• TPRE[1:0] = 2: Timer period is 10ms

• TPRE[1:0] = 3: Timer period is 20ms

A higher timer period leads to lower soft pre-

startup current, but increases pre-startup time.

Cycle-by-Cycle

Over-Current

Protection

(OCP)

During normal switching, if the current flowing

through the MOSFET exceeds the threshold set

by register bits OCP[1:0] after a set blanking

time, then the high-side MOSFETs (HS-FETs)

turn off and the low-side MOSFETs (LS-FETs)