UM1494

Triac control

Doc ID 022519 Rev 1

13/23

4

Triac control

4.1

Maximum allowed load current

Maximum allowed current depends on the ability of the device to dissipate the energy into

ambient to keep the junction of the device at 125 °C (150 °C for high temperature Triac).

Refer also to AN533.

Dissipated power for full wave operation is given by:

Equation 1 Dissipated power estimation

Maximum junction temperature of the device is then:

Equation 2 Maximum junction temperature estimation

resistance. Thermal resistance consists of one part in the case of SMD package and is

defined in the datasheet depending on the PCB heatsink area.

Table 2 gives the maximum RMS current each ACS/Triac can control, at maximum ambient

temperature 60 °C, to keep junction temperature below max. allowed value.

Higher load current can be controlled using forced cooling. The AN533 is dedicated for a full

description of thermal management.

4.2

Gate current width and minimum load current

Gate current pulse is generated by the MCU. The length of the pulse is set by software and

can be changed separately for each load. Gate current pulse length is an important value to

be set according to minimum load current. Load current must reach latching current level to

switch datasheet. It is important to check for low power loads when RMS current is low as it

takes a longer time for the load current to reach latching current level. When gate current is

Table 2.

AC switch

Package

PCB heatsink

(°C/W)

RMS current

(A)

(W)

ACS108

SMBFlat

1

115

0.56

0.55

T1010H-6G

D2PAK

3

40

2.6

2.15

P

d

V

to

l

RM S

R

(

+

•

=

T

j

T

amb

P

d

R

th j

a

–

()

•

+

=