STDRIVE102BH datasheet(42/56 Pages) STMICROELECTRONICS

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Layout recommendations and guidelines

7.1

Power stage layout

It is very important to minimize the overall parasitic inductance of the paths connecting the power MOSFETs and

the gate drivers. Higher inductance can introduce ringing on the gate signals and increase induced turn-on

effects. In order to minimize inductance:

•

The traces between the STDRIVE102BH/H and the MOSFETs must be as short and straight as possible.

•

The traces should avoid multiple transitions between PCB layers.

•

When moving away from the STDRIVE102BH/H pads, increase the trace width (at least 0.5 mm).

•

Each couple of traces GHSx/OUTx and GLSx/SLSx must follow the same path and should be routed one

close to the other to minimize their loop area.

•

Place a ground plane with no discontinuities underneath the power stage, to provide the shortest return

path for the gate currents (see Section 7.2).

A wide copper area must connect the drains of the three high-side MOSFETs, the motor’s supply VM and the bulk

capacitors. The area can be replicated in the inner layers of the PCB; all of them can be connected using multiple

vias. This approach decreases the overall impedance and improves the thermal dissipation of the high-side

section of the power stage. Extend the VM copper area underneath the gate driver traces, then connect it to the

VM pin of the STDRIVE102BH/H; this ensures a return path for the currents provided by the charge pump.

Moreover, the VM pin is also used to sense the high-side drains for the VDS monitoring protection: wider copper

areas help to reduce the voltage drop along this path. A low ESR ceramic capacitor must be placed close to the

VM pin (see Section 7.3).

The high-side source and the low-side drain in each half-bridge should be connected with a dedicated copper

area, which then connects to each motor’s phase. Similarly, the low-side source and the shunt resistor in each

half-bridge should be connected with a dedicated copper area. Each copper area can be replicated on different

layers; all of them must be connected with an adequate number of vias. Vias concentration should be higher close

to the pads of the power components (MOSFETs and shunt resistors). This allows to have a low impedance path

for the load currents and helps to dissipate the heat.

Do not use the same trace to connect different branches, even if they share the same net: for example, SLSx

coming from the STDRIVE102BH/H needs a dedicated trace, which directly connects the source of the low-side

MOSFET. Then a wide copper area must connect the source of the low-side MOSFET and the shunt resistor.

Eventually, another dedicated pair of differential traces is routed from the two pads of the shunt resistor to the

readout circuitry.

Other signals not directly related to the power stage should be routed in a different area of the PCB, to avoid any

noise coupling due to high dV/dt and dI/dt transients.

7.2

Grounding

One inner layer of the PCB should be dedicated only for grounding. The layer should be divided in two planes:

one for the power part and another for the low-voltage signal part. The two planes are tied together in

correspondence with the STDRIVE102BH/H, which should be placed in the middle of the two. Power ground

plane must be connected to the exposed pad (GND) of the STDRIVE102BH/H, while the signal ground plane

should be connected to the AGND pin. The junction between AGND and the exposed pad (GND) must be done

as close as possible to the STDRIVE102BH/H in order to minimize grounds misalignment. Exposed pad must

have an adequate number of vias to transfer heat to the other layers, down to the bottom layer of the PCB, in

order to dissipate heat.

Therefore, the PCB can be divided in two main areas, delimited by each plane: the power area and the signal

area. Routing of the components related to the operational amplifiers and in general to the circuitries related to

VDD, including the resistors’ divider for TCC and IGATE pins, must be placed in the signal ground area. On the

other hand, the power ground area should be dedicated only to the power stage, the gate drivers’ traces, the

copper plane of the VM supply, the bulk capacitor and all the ceramic capacitors connected to each half-bridge.

STDRIVE102BH, STDRIVE102H

Layout recommendations and

guidelines

DS14545 - Rev 1

page 42/56

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