ST has released a family of low voltage motor control drivers.
This family consists of three products:
STSPIN220 : a low voltage stepper motor driver
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STSPIN230 : a low voltage triple half-bridge motor driver for BLDC motors
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STSPIN240 : a low voltage databrush DC motor
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Based on the same silicon, these products share common characteristics; first, they come in a small QFN 3x3 package. The RDson of high side + low side is typically 0.4 Ohm, meaning at 25⁰ C. But when you design a motor control application, it’s better to take the maximum at 125⁰ C, otherwise the calculation of the max current will be too optimistic. Indeed, even if the datasheet states a current of 1.3 A RMS, you have to keep in mind that this value is the current the die can withstand, not the max current the application can drain. Due to power dissipation, the current will be lower. The power dissipation depends on the package, the layout of the board (area and thickness of copper), and the heat generated by the other components on the board. To get an estimation of the current the application can withstand, we can assume an RDson of 0.8 Ohm (at 125o C, we double the resistance given at 25o C) and a power dissipation of 50 o C/W. The power to dissipate is resistance * current^2, so in our case, 0.8 * 1.3^2 = 1.35W. With the assumed power dissipation, that means an increase of 67o C. Even in a consumer application, this increase in temperature will probably result in overtemperature shut down. Besides, in a stepper or BLDC motors, two bridges must drain the same RMS current, and there is no way to dissipate all this energy.
The STSPIN2x family of products integrates an overtemperature protection. If the die temperature reaches 160o C, the chip automatically shuts down. In practice, if the temperature reaches 125o C, due to the RDson increasing exponentially, overtemperature will occur. Overtemperature conditions come about due to extra current, so STSPIN2x also integrates an overcurrent protection and a short-circuit protection.
In order to estimate the highest current the application can drain, it is necessary to know the highest environment temperature and the power dissipation of the board. Having this information allows us to calculate the power margin, and by knowing the resistance of the bridge and how many bridges are used, you can calculate the max current.
Only one voltage supply is necessary from 1.8 to 10V. As these devices target low power and portable devices like printers, it is necessary to have very low power shut down. The STSPIN products have a standby pin that makes it possible to put the device in shut down and consume only 10nA.
When designing medium or high power motor control, a charge pump is necessary to drive the high side. In a low power design, the high side can be a PMOS unlike an NMOS in high power solution and hence the gate can be referenced to ground to be turned on. This simplifies the design, as the charge pump is a common source of failures.
DC motors are often used in the toy industry, as they are cheap and easy to drive. The STSPIN240 is a dual H-bridge that can drive two DC motors. Two PWM current controllers, one for each bridge, are integrated. An RC circuit on the toff pin allows for the programming of decay timing. The decay is always a slow decay by recirculation of the current in the low side.
The driving of a stepper motor can be considered as the driving of two DC motors with a 90 degree phase difference. The STSPIN220 is a low voltage stepper motor driver able to drive up to 256 microsteps. When you design such tiny microsteps, it is mainly for marketing purposes. From an engineering stand point, it is not very logical. Indeed, if a bridge is switched too often, switching power losses can be significant and even higher than conducting losses. It is recommended to avoid switching faster than 50kHz. In theory, that would be translated to a maximum speed of 200 full step/s, and in real life it would occur at a lower speed. That means a 256 microstep configuration can be used only at very low speeds. And even at low speed, the noise would be larger than the microstep. Indeed, if the bridge is ON for 10 microseconds in a 5V application in 2mH inductance for a motor, the voltage would increase by 100mV. This must be compared to the difference of voltage equal to 68mV between two microsteps in the middle of the full step, in other words at sin(pi/4). The STSPIN220 is the best in class in its category, but a designer must be aware that the smallest microstep is not necessarily the right fit in his application. Fortunately, the STSPIN220 can be configured to run in full, ½, ¼, 1/8, 1/16, 1/32, 1/64, 1/128 or 1/256 step. When running at high speed, the STSPIN220 can be easily forced to full step by putting two pins called MODE1 and MODE2 to ground. The previous condition is restored as soon as the MODE1 and MODE2 inputs switch to a different combination.
To drive the motor, one pin is used for the direction and one pin is used to move to the next microstep. Each H-bridge has a PWM current controller. The frequency is programmed thanks to an RC circuit on the T0FF pin. The TOFF time is then split in 5/8 for a slow decay and 3/8 for a fast decay. This configuration greatly simplifies the driving of the motor.
Finally, the BLDC version is the STSPIN230. This kind of motor is used when the speed of motor has to be pretty fast and hence is used in drones, for example. The STSPIN230 has three half bridges, each one controlled by two pins. As there is no PWM current control, an interlocking protection is added to this device to avoid a short-circuit between ground and Vcc.
To conclude, whatever type of motor you need to drive in a low power application, the STSPIN2x family provides state-of-the-art solution, with Arduino for factor evalboards to meet maker and professional requirements.