ACS triggering mode

AN1172

4/23

1.2

New layout possibilities

It has already been said that ACS silicon structure is different from the triac, according to the

gate operation. A second difference is that ACS have been developed in an integration goal.

To allow different cells to be associated in one single package or controlled by one single

drive die, the common drive reference voltage must be connected to the back of the die.

Indeed, each die bottom is electrically linked to the other ones by the frame. This is achieved

by the ACS silicon structure, where an integrated level shifter allows both thyristors to be

controlled by means of a gate voltage referenced at the back of the die (COM pin). (See

References, 1.).

Thanks to ACSs arrays, the copper tracks count is reduced since the different COM pins are

connected together inside the package. This also allows smaller gate / MCU copper tracks

loop areas, and so increases the EMI immunity of the overall electronic board. Figure 2.

shows an example of connection between an ACS402-5SB4 and an ST62xx, both in DIL20

packages.

Figure 2.

Reduction of gate / MCU loop areas

A particular benefit of such a pin out appears with Surface Mount Devices (SMD). In this

case, the tab pin is the COM one. The copper surface used to perform a heat-sink can then

be used as a supply voltage bus. It allows new layout possibilities and, above all, a

miniaturization of the Printed Circuit Board (PCB). Indeed, unlike triacs, the heat-sink areas

are at the same voltage and so can be regrouped (see Figure 3.). The heatsink area

therefore depends on the maximum amount of dissipated power at the same time, by all the

switches put on it. So, the number of switches which will conduct at the same time and their

conduction time should be known.

Figure 3.

Printed circuit area reduction thanks to ACSs in SOT223 packages

ACS402

1

PA0

PA1

PA2

PA3

OUT1

OUT2

OUT3

OUT4

1

G1

G2

G3

G4

COM

Vdd

ST6

Rg

MCU

Ref.

G

OUT

COM

LOAD

COPPER HEATSINK

G

OUT

COM

LOAD

PCB required for ACSs

G

A2

A1

A2

A2

LOAD

MCU

Ref.

G

A2

A1

A2

LOAD

Copper heatsink

PCB required for Triacs

PCB required for Triacs

A2