Yes, you can download a demonstration board schematic and bill of materials for the A3959 on the Allegro Web site, at http://prostores2.carrierzone.com/servlet/AllegroMicroSystems/StoreFront, free of charge. Also, for a small fee, you can purchase the demonstration board.

Q2: What types of protection features does the A3959 offer?

The following protection features are provided:

Thermal shut down (TSD)
Undervoltage lockout (UVLO)
Crossover current protection
V_REG and charge pump monitors

Q3: What types of external components are required?

The following components are required for correct operation of the A3959:

R_S, the external sense resistor, is required for the PWM current control circuit. This should be a noninductive type of resistor. Recommended maximum R_S value can be calculated using R_S = 0.5 / I_TRIP(max). Using a reasonably smaller value for R_S will dissipate less power in R_S and provide headroom. There also needs to be a 0.1 µF mono/ceramic capacitor in parallel with the sense resistor.
A 0.22 µF mono/ceramic capacitor must be placed between the CP1 and CP2 pins.
The VREG pin should be decoupled with a 0.22 µF capacitor to ground.
A LOGIC SUPPLY (V_DD) decoupling capacitor is recommended: ceramic, rated at 0.1 µF.
A LOAD SUPPLY (V_BB) decoupling capacitor is recommended: electrolytic, rated at >47 µF. In addition, a 0.1 µF ceramic capacitor should be placed in parallel, if high frequency issues are a concern.
If the SLEEP pin is not used, a 1 kΩ pull-up resistor to V_DD is required.

Q4: Do I need pull-up/pull-down resistors on the input pins?

Not necessarily. The inputs can be tied directly to V_DD or ground, depending on the logic level you desire. If pull-up/pull-down resistors are required for your particular design, 1 k to 4.7 kΩ resistors are recommended.

Q5: What is the maximum allowable motor supply voltage?

50 V. This must not be exceeded under any circumstances.

Q6: The datasheet states an output current of ±3.0 A. Is this a peak current for the device, or a continuous current?

The output current rating is for continuous current. The A3959 can handle a peak current of 6 A for <3 µs. Note: When running at high currents, power dissipation should be carefully considered. Caution should be taken to never exceed a junction temperature of 150°C when running the device.

Q7: Is the A3959 a constant-current or a constant-voltage controlled device?

The A3959 provides constant-current control. Motor winding current is controlled by an internal PWM current-control circuit, which incorporates an internal OSC circuit to set the fixed off-time, which is typically 24 µs.

Q8: Are there any layout concerns I should be aware of?

Yes. The sense resistor, R_S, should be connected as close as possible to the device. The ground side of R_S should return on a separate trace to the ground pin(s) of the device. R_S should be noninductive, and the circuit board traces should be as large as physically possible. A 47 µF or larger electrolytic decoupling capacitor should be placed between the load supply pins and ground, and be placed as close as physically possible to the device.

Q9: What is the recommended minimum copper ground plane area for reducing power dissipation at high currents?

A ground plane area that is at least two times larger than the package outline is a good place to start. For further layout considerations, please refer to the following on the Allegro Web site: "Package Thermal Characteristics," at http://www.allegromicro.com/en/Products/Design/thrmlchr/thrmlchr.pdf.

Q10: Are there special techniques to reduce the package power dissipation when running at high currents?

Use of external Schottky diodes with low V_FORWARD, to clamp the outputs to V_BB and ground, will help to reduce the power dissipation in the A3959. Heat sinks are also a possibility, but not as efficient. For additional information, please refer to the following, on the Allegro Web site: "Power Drive Circuits," at http://www.allegromicro.com/en/Products/Design/an/AN295048.pdf.

Q11: Is there an application note on the use of external diodes?

There is no application note about using external diodes on the A3959. Each of the outputs should have one Schottky diode connected to V_BB (cathode to V_BB) and one Schottky diode connected to ground (anode to ground, not to the sense pins). If the PFD1 and PDF2 input pins are set to "slow decay only," then use only two Schottky diodes between the outputs and ground. The two Schottky diodes from the outputs to V_BB will not help improve thermal performance in slow decay mode.

Q12: Do you have a recommended Schottky diode?

We typically don't recommend a specific diode, due to the range of voltages and currents that can be used.

Q13: Can I run the maximum rated output current for each package option?

It is possible. However, there are several considerations, such as optimization of circuit board layout, use of heat sinks, etc. Please refer to application note numbers: AN29501.4, "Computing IC Temperature Rise," at http://www.allegromicro.com/en/Products/Design/an/an295014.pdf and 29501.5, "Improving Batwing Power Dissipation," at http://www.allegromicro.com/en/Products/Design/an/an295015.pdf.

Q14: Is the A3959 capable of being used in portable applications?

Absolutely. The A3959 has Sleep mode, which minimizes power consumption when not in use. During Sleep mode, the device draws a maximum of 20 µA.

Q15: Is there an application note for the A3959?

Unfortunately, not at this time. However, the datasheet and these FAQs address the majority of the questions regarding the A3959.

Q16: Is there a drop-in, or pin-for-pin, replacement for the A3959?

No. The A3959 is generally a more cost-effective solution than most typical motor driver ICs due to its 3 A capability.

High-Performance Power ICs and Hall-Effect Sensors

Related Links:

FAQs - A3959 DMOS Full-Bridge PWM Motor Driver