5V to 26V, 5.5A Three-Phase Brushless DC Motor Driver Evaluation Board

November 15, 2018 by Paul Shepard

The EV6536-U-00A from Monolithic Power Systems is the evaluation board for the MP6536, a three-phase BLDC motor driver. It accepts pwm modulated inputs for operation.

The MP6536 features a low current shutdown mode, standby mode, input under voltage protection, current limit, thermal shutdown and fault flag signal output. All channels of the drivers interface with standard logic signals.

The MP6536 is available in a 40 lead QFN 5mm x 5mm package.

The output of the MP6536 is in phase with the input, and the dead time is optimized for symmetrical performance, regardless of load conditions.

When SHDN is low, all channels are off. When STBYB is pulled low, it causes the outputs of all the channels to go into high impedance.

However, when the voltage across BST1/2/3 and SW1/2/3 drops low significantly, the bottom MOSFET is turned on to refresh the external bootstrap capacitor. Connecting a capacitor (0.1μF or greater) between BST and SW (as the bootstrap capacitor) is recommended.

In order to prevent erratic operation, two undervoltage lockout (UVLO) circuits are used. One ensures that the supply for the bottom gate drive circuit is sufficiently high, and the other is for the top gate driver.

MPS65326 block diagram (one half-bridge channel only)

Fault Protection

To protect the power MOSFETs, an internal current limit of 5.5A is set for all MOSFETs. When this limit is reached, all MOSFETs of the over-current bridge channel will go into high impedance for a fixed duration (30µs approximately) before resuming normal operation.

Thermal monitoring is integrated into the MP6536. If the die temperature rises above 160ºC, all switches are turned off. The temperature must all below 125ºC before normal operation resumes.

To enhance the robustness of the device under a short-circuit condition, a capacitor can be connected to FAULTB. The time constant of the RC must be greater than 50ms for the FAULTB node to reach 2V.

Under a short-circuit condition, the FAULTB node re-sets to zero, and the part is placed in standby mode until the voltage at STBYB is above 2V.

Fault Output

The MP6536 includes an open drain, active-low fault indicator output (FAULTB). A fault is indicated if one of the following conditions is detected:

  1. The current limit is tripped.
  2. Thermal shutdown is tripped.

A fault on any channel causes FAULTB to pull low. Once the fault is removed, the MP6536 resumes normal operation.

Error Reporting

The MP6536 has two fault monitor pins (FLT3B and FLT2B), which are active low open-drain outputs. They provide protection-mode signaling to a PWM controller or another system control device.

MPS6536 circuit board

EV6536-U-00A summary of features:

  • 5V to 26V VDD
  • ±5.5A Peak Current Output
  • Up to 1MHz Switching Frequency
  • Current Sense Output
  • Optional 3.3V or 5V Logic Power Supply on Board
  • All Switches Current Limited
  • Internal Under Voltage Protection
  • Internal Thermal Protection
  • Short-circuit Protection
  • Fault Output Flag