AN2986 datasheet(9/18 Pages) STMICROELECTRONICS

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AN2986

Gate current variation

Doc ID 15727 Rev 1

9/18

Gate current variation

2.1

VGT variation

The voltage drop of the gate junction VGT varies with temperature and load current. The VGT

variation with temperature can be estimated as 2 mV/ °C.

VGT variation with load current is greater and so has a higher influence on gate current

variation. For example Figure 3 gives VGT variation (dark blue curve) during an entire mains

cycle for Z0103 with a 1 A 50 Hz RMS load current

The characterization of the peak value reached by the gate to A1 (or COM) voltage (refer to

"VGTpeak" in Figure 3) is provided when the AC switch current reaches its peak value (refer

to "ITpeak"). The measurements were taken under the following conditions:

●

VDD voltage level: 3.3 V

●

RG resistance: 200 Ω for Z0103 and 100 Ω for other devices

With these values and using the MCU (ST7FLITE19B), the gate current (for zero-load

current) is 7.5 mA with the Z0103. This value is called "IG0".

The VGT variation with load current is larger and significant for positive half-wave. Figure 4

shows that VGT becomes negative and its value drops to –84 mV with a 1.44 A IT current.

This VGT variation has a significant impact on the current consumption and cannot be

neglected. See Figure 4 and Figure 5 for graphs of VGT variation versus load current for

Z0103 and ACS108-6T.

Figure 3.

VGT variation with load current in quadrants 2 and 3 (0.2 A RMS) for Z0103

(Tj = 85 °C, IG0 = 7.5 mA)

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