AN2986 datasheet(5/18 Pages) STMICROELECTRONICS

5 / 18 page

AN2986

Gate resistor choice

Doc ID 15727 Rev 1

5/18

Gate resistor choice

1.1

Variation of gate current with temperature

The value of the gate resistor (refer to RG in Figure 1, where a negative power supply is

used) is determined to ensure proper turn-on of the ACS™/TRIAC in the temperature range

specified by the application. The minimum gate current required for turn-on of the

ACS/TRIAC increases as the junction temperature decreases. This variation of minimum

gate current is described in the datasheet “Z01 - 1 A Triacs”, see example in Figure 2. The

worst case appears when junction temperature Tj is at minimum ambient temperature.

Minimum ambient temperature is set to 0 °C for most home appliance applications.

The gate current (IGT) level is specified for 25 °C. At temperature 0 °C this level is usually

increased to a range 1.3 - 1.5 times higher for most TRIACs and AC switches.

Figure 1.

Circuit for direct driving of ACS/TRIAC from MCU

Figure 1 also gives the references for the electrical parameters (VT, IT, VG) which are used in

this application note. Please note that voltage VG is referenced to the G terminal, not the A1

or COM terminal in order to get positive values when the current is sunk from the gate.

AM00456

VAC MAINS

Load

COM/A1

OUT/A2

ACS/TRIAC

MCU

VDD

VSS

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