This is the A3977 based steping motor driver board I've designed. The goal was to make board that is small enough to fit three axis system on 160x80 mm euro card.

It was designed to be as flexible as possible. All chip logic inputs can be adjusted with jumpers. Board also has some additional features like protection for reverse polarity and overvoltage situations. I also left some space around the chip to make it possible to attach a heat sink.

I also attempted to design the board with good EMC properties. For example see those high current output traces that are placed on both sides to minimize current loops that would cause parasitic inductance.

Thanks for MrBean from the CNCzone for the nice render :)

I don't currently have any spare boards to sell. You can use my Eagle files (see the bottom of the page) to produce or order your own boards.

A3977 chip standard features:

• Step/dir interface
• Peak current output 2.5 A or 1.77 A RMS
• Stepping configurations: 1/8, 1/4, 1/2 (half step) and 1/1 (full step)
• Mixed mode decay (PFD). Helps to minimize motor noise and heating.
• Synchronous rectification to reduce chip power dissipation when not using output diodes.
• Over heating and under voltage shutdown.

For details see Allegro 3977 product page.

Additional features provided by this board:

• Reverse polarity protection diode (optional)
• Over voltage protection. Also protects against motor's back EMF situations when braking stepper rapidly. (optional)
• "Feature connector" pin+pad in control terminal. Can be used to control any logic input of the chip.
• Rectification diodes for output to reduce chip heating (optional)
• Most jumpers are hard wired in default position to eliminate unnecessary jumpers. Thin hard wiring trace can be disconnected if jumper will be used.
• On board regulator for logic voltage.
• Adjustment trimmer for motor current and PFD.
• Board size 80x53 mm.
• Silkscreen and solder mask.

Here is the list of components. Some parts are optional, see the description below.


Part     Value         Package
C1       220n          C050-050X075
C2       220n          C050-050X075
C3       220-470u      E5-10,5
C4       220-330u      E2,5-7
C5       0.22u         C050-030X075
C6       0.22u         C050-030X075
C7       0.22u         C050-030X075
C8       0.001u        C025-025X050
C9       0.001u        C025-025X050
C10      0.1u          C050-025X075
C11      0.1u          C050-025X075
C12      0.1u          C050-025X075
C13      0.1u          C050-025X075
C14      0.1u          C050-025X075
C15      0.1u          C050-025X075
C16      47u           E2,5-6
C17      47u           E2,5-6
**D1     BYV27         DIODE
**D2     BYV27         DIODE
**D3     BYV27         DIODE
**D4     BYV27         DIODE
**D5     BYV27         DIODE
**D6     BYV27         DIODE
**D7     BYV27         DIODE
**D8     BYV27         DIODE
*D9      Vz=34V        DO34Z7
*D10     PBYR1645      TO220
****EN                 JP1
IC1      A3977SED      PLCC44
IC2      7805          TO220
***JP1                 JP2Q
JP3                    1X06
***JP7                 JP2Q
****JREF               JP1
MS1                    JP1
MS2                    JP1
PFD      1k            PT-10
*Q2      TIP120-TIP122 TO220
R1       30k           0207/2V
R2       30k           0207/2V
R3       0.20 (2W)     0411V
R4       0.20 (2W)     0411V
*R5      10k           0207/2V
R8       680-820       R1206
R13      10k           0207/2V
R14      10k           R1206
R15      10k           R1206
R16      10k           R1206
R17      10k           R1206
R18      10k           R1206
REF      1k            PT-10
****RST                JP1
****SLP                JP1
****SR                 JP1
X2                     AK500/2
X3       AK550/2       AK550/2
X4       AK550/2       AK550/2


Parts marked with stars are optional:

*	Overvoltage and reverse polarity protection
**	Decreases power dissipation of the chip. SR jumper must be open to get the advantage of the diodes.
***	May be used in some future expansion.
****	Hard wired jumpers. See description in next chapter.

Capacitors below 1 µF are ceramic type.

All 10k Ohm SMD resistors are controlling logic only. You can use any resistor between 5-30 kOhm.

C16 and C17 have very limited space. Try to find largest capacitor that fits in board. Capacitor volrage rating must be at least 35V.

D10 can be almost any diode that will not break when applying reverse polarity supply voltage.

X3 and X4 are smaller type screw terminals! Lead spacing about 3.5 mm.

If you are going to solder D1-D8 don't forget to solder two jump wires near diodes!

Please see the picture about hard wired jumpers.

Jumpers SLP (sleep), RST (reset) and EN (enable) are hard wired by default the way the chip becomes active. You probly don't want to modify these.

Jumper SR (synchronous rectification) is hard wired ON by default. This means you can leave it untouched if you are not going to solder diodes D1-D8. If you decide to solder diodes then cut the hard wiring and solder R17 (and jumper SR if you wish to change setting on fly).

Jumper JREF can be used to control motor current with external circuit. By default current is controlled only by trimmer REF.

Jumpers MS1 and MS2 set microstepping resolution:

	MS2	MS1
Full step	open	open
1/2	open	short
1/4	short	open
1/8	short	short

Note that MS1 and MS2 does NOT have hard wired settings. You must solder the jumpers and resistor.

See the picture for pinouts.

JP3 descriptions:

HOME OUT	Outputs one logig level (0..5V) pulse on every full step. Most people won't need this.
DIR	Direction input. A logig level input for direction of next step.
STEP	Step input. When short (minimum 1μS pulse) logic level pulse is applied to STEP input motor will rotate one microstep in direction defined by DIR.
FC	Not connected by default.
+5V	A regulated 5V output.
GND	Ground terminal.

In most cases user needs only GND, STEP and DIR pins.

Power connector

POWER +	A positive input voltage. Max 35 Vdc.
POWER -	Power ground.

First of all, board works as expected. Steppers run very smooth with 1/8 microstepping and mixed mode decay reduces stepper iron losses and heating.

I tried to run a Nema 23 sized 0.5 Nm 3 amp motor with prototype board. Without load stepper could reach little over 220 000 microsteps per second or 8250 rpm! I didn't know that stepping motor would be able to run such speeds. Of course this kind of speed is not very practical due to stepper's low torque at high speeds.

A3977 chip gets hot when current is set over 1.5 amps. Some heat sink surely would't hurt. Hovewer one should remember that about 60 celsius feels hot to finger but it's relatively cool to IC.

Here are the Eagle layout files for the board. You may freerly use these on your non-profit projects.

teros_a3977.tar.gz - Schematics and layout, 60 KiB