Smart door lock motor driver IC design scheme with dynamic over-current detection function

This article introduces a smart door lock motor drive integrated Circuit (IC) design with dynamic overcurrent detection function, which can support different power supply voltages and loads.

This article introduces a smart door lock motor drive integrated circuit (IC) design with dynamic overcurrent detection function, which can support different power supply voltages and loads.

Currently, most smart door locks use battery power. The battery life is usually about 6 months, up to a year. The length of battery life depends ON the wireless technology used (Wi-Fi, Bluetooth, ZigBee) and how often the door lock is opened and closed.

The motor in this design example is powered by four AA batteries.

Smart door lock manufacturers use different methods to detect the complete state of the bolt opening or closing: limit switches, accelerometers fixed on the shaft, Hall sensors and magnet sets on gears, etc. They all require corresponding external components and motor drive ICs.

One of the methods for detecting the position of the bolt is to measure the motor current. When the bolt is locked, the motor is turned off, and the motor current also rises to a defined threshold (see Figure 1). This method does not require additional components. However, the threshold must be determined according to the corresponding specific power supply voltage, which is usually the battery Voltage in a fully charged state.

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 1: Motor current waveform

An improvement of the design is to measure the root mean square (RMS) current of each motor and set different current thresholds to compensate for different battery voltages (see Figure 2). This article describes how to configure the internal logic resources of the high-voltage GreenPAK™ IC for this design scheme.

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 2: Motor current waveform with compensation

Configuration and operating principles

1. Operating principle

The design is divided into three parts, as shown in Figure 3:

Motor stall detection: If the motor current is too high 100ms after the motor is started, the motor drive control chip closes its internal mechanism and measures and corrects the motor current.

Current protection threshold setting: The Vref of the current CMP (the internal logic resource of the GreenPAK™ IC) depends on the motor operating current (set to be higher than the measured value).

Over-current waiting: If the working current of the motor is higher than the selected value during this period, the motor will be shut down.

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 3: Design run

2. HV GreenPAK internal resource allocation/design

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 4: HV GreenPAK design

The current CMP register file (RegFile) is used to measure the motor current. There are 16 values, and they switch from high to low (see Figure 5).

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 5: RegFile data

After 250 ms, the register file will switch up two values ​​(for example, it will reach the value of Byte8 before 250ms, and switch to the value of Byte10 after 250ms) to set a new current threshold, as shown in Figure 6. When the motor current increases to this new current threshold, the mechanism will shut down (see Figure 7).

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 6: Register file usage

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 7: Motor shutdown process

For different power supply voltages and loads, the motor current will be different. For higher motor currents, the “motor shutdown protection current level” will become higher.

Application circuit

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 8: Typical application circuit

• PIN#2 motor ON ―> the rising edge turns on the motor
• PIN#3 motor direction ―> motor rotation direction: HIGH ―> forward rotation, LOW ―> reverse rotation
• VDD range: 2.3 VC 5.5 V
• VDD2 range: 3.6 VC 6.0 V

Motor test

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Table 1: Motor parameters

When the power supply voltage is 6.0 V, the peak value of the motor starting current is about 2A, and it will decrease to the nominal value after 200ms. The specific value depends on the power supply voltage (see Figure 9-12).

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 9: Motor starting current waveform, power supply voltage 3.6 V

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 10: Motor no-load current, power supply voltage 3.6 V

Figure 11: Motor starting current waveform, power supply voltage 6.0 V

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 12: Motor no-load current, power supply voltage 6.0 V

Design running waveform

normal operation

• Power supply voltage: 6.0 V
• Root mean square (RMS) current of the motor: 170 mA
• Motor shutdown protection current: 620 mA

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 13: No-load motor, power supply voltage 6.0 V

• Power supply voltage: 3.6 V
• Root mean square (RMS) current of the motor: 127 mA
• Motor shutdown protection current: 460 mA

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 14: No-load motor, power supply voltage 3.6 V

• Power supply voltage: 3.0 V
• Root mean square (RMS) current of the motor: 310 mA
• Motor shutdown protection current: 670 mA

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 15: Load motor, power supply voltage 3.0 V

Motor stalls when starting

The motor stall detection time is 100 ms. If the motor current is high within 100 ms after starting, the motor drive will automatically shut down.

Smart door lock motor driver IC design scheme with dynamic over-current detection function
Figure 16: Motor stalled, power supply voltage 3.6 VC 6.0 V

Summarize

This article introduces a specific example of how to use Dialog’s high-voltage GreenPAK chip, explaining the custom design of integrated Circuits for specific motors and battery packs. This is a very flexible motor control and drive solution that uses configurable internal logic to support the designer’s preferences. The integration of the motor drive in the GreenPAK chip means that the entire circuit can be fitted into a small physical space.

When the motor current or power supply voltage changes, the designer can customize the circuit. GreenPAK chips can also be used to design constant current and constant voltage motor drive control schemes, and have embedded protection functions, such as overcurrent, undervoltage, and overtemperature protection.

The Links:   LM150X08-TLC1 CMC-GG1790DFCW-N-E-V1