The availability of mid-range power drivers for small motors in the industrial market space is very limited at present, and often times a discrete circuit is considered as the only option. With the addition of the SA306-IHZ and SA57-IHZ to the Apex Precision Power product family, customers can now chose a very efficient, low cost pulse width modulation (PWM) IC for operation with either a brushless or brush DC motor rated for supply voltages of less than 9V, all the way up to 60V. As monolithic, single package solutions, both the SA306-IHZ and the SA57-IHZ offer a very attractive option versus discrete designs. Starting with their power ratings, both ICs can provide 5A of continuous output current and 17A PEAK. An even higher 8A of continuous output current is possible by selecting the A-Grade versions of each device – the SA306A-IHZ or the SA57A-IHZ. In terms of board real estate, both ICs are available in a 64-pin PowerQuad package (PowerQFP) that measures less than two inches square. In sharp contrast, a discrete design would need to incorporate gate drivers, power FETs and ancillary components, which in total, would stretch out on a PCB and thus require an additional 50% to 70% of valuable board space. A discrete design also requires the expense and resources to procure and build the circuit itself. An additional challenge becomes that of reliability in terms of component testing and circuit board connections. An off-the-shelf solution like the SA306-IHZ or the SA57-IHZ reduces de-bugging, reduces the burden of inventory overhead, reduces the taxing of design resources, and in return, speeds up the product launch cycle.

Cycle-by-Cycle Current Limit
Taking a closer look at the very unique performance features for both the SA306-IHZ andthe SA57-IHZ, the most advanced feature is the “cycle-by-cycle” current limit. In many motor applications, the ability to control the current is a very common requirement. Typically, the motor’s current is directly controlled by the processor or DSP in order to achieve optimum performance. With the cycle-by-cycle current limit function of the SA306-IHZ and the SA57-IHZ, the feedback signals are sent to the processor in real time for each motor phase. The cycle-by-cycle current limit function is actually a hardware feature of both ICs which continuously monitors and regulates the current in all motor phases and compares current levels to a pre-determined “safe” limit. If the limit is exceeded, the IC will shut down all outputs for the remainder of the switching cycle and re-set the outputs at the start of the next cycle, hence the terminology “cycle-by-cycle” current limit. Just to clarify, current control calculations typically tax the bandwidth of the processor in motor control systems as it handles the interrupt service routine with the high bandwidth signal of the motor. But with the application of the SA306-IHZ and the SA57-IHZ, high speed current mode control can be handled by the processor rather than just settle for limiting the current to a safe value.

Motor Soft Start
A piggy-back benefit of having cycle-by-cycle current limit functionality with both devices is the ability to soft start the motor. In fact, without cycle-by-cycle current limiting, the motor’s continuous current rating must be de-rated with respect to the current rating of the amplifier to allow for start-up inrush current. Using a 1A continuous motor as an example, it may require up to 10A PEAK of inrush current to accelerate the motor up to speed. With the functionality of cycle-by-cycle current limit, de-rating is not necessary. Both the SA306-IHZ and the SA57-IHZ can work with motors rated up to 5A continuous or more. The motor will start up “gently” because the inrush current is limited.

Digital Interface
The SA306-IHZ and the SA57-IHZ are both designed to provide a clean interface signal to a digital microcontroller (MCU) or DSP. Each top side and bottom side output FET can be individually controlled via signals from the processor. Communication between the driver and the processor includes current sensing for each phase and is supplied as individual inputs to the ADC of the processor. Short circuit protection and high temperature sensing is handled as digital feedback signals. Communication with the motor is the responsibility of the processor. In the case of a brushless motor, the processor changes the PWM signals to the top transistors, as well as the ON-OFF signals to the bottom transistors. This is based on the three hall-effect feedback signals in the case of the brushless motor which indicates position of the rotor. For a brush motor, the PWM signals work between the SA57-IHZ’s dual power stages and the motor.

Brushless vs Brush
In making the choice to go “off-the-shelf” with either the SA306-IHZ or the SA57-IHZ, there is a specific difference in their topology for motor interface. The SA306-IHZ is a brushless (BLDC) DC motor driver; whereas, the SA57-IHZ is designed to drive brush DC motors. Selection of the motor type for a particular application is strictly a matter of user preference. Typically, a brushless motor is used in operating environments that need to remain relatively clean, and where maintenance and downtime must be kept to a minimum. A brush motor solution is more suited to lower cost, more rugged operating environments, where the dust generated by the motor’s brushes, as well as regularly scheduled maintenance to replace those brushes, will not create a hardship. The SA306-IHZ has a three-phase output consisting of two totem-pole transistors per output. This typology enables the device to drive a brushless DC motor. The SA306-IHZ is also capable of driving MULTIPLE brush DC motors! If bi-directional rotation is not required, then the SA306-IHZ can drive three independent brush motors at the same time. If the application does call for bi-directional rotation, then the IC can drive two brush motors one at a time. If only a single brush DC motor is to be driven, then the SA57-IHZ is the most economical solution. For the SA57-IHZ, getting a brush motor to spin is extremely easy. The IC utilizes just two power stages to drive the motor’s two brushes. The brushes in turn control the motor’s three coils.