2.5 Output Description

The output of the Si875x device develops a positive voltage on the GATE pin with respect to the SOURCE pin. This voltage is used to

turn on a typical field effect transistor (FET). Because power is transmitted across the isolation barrier, no isolated supply is required.

This can be used to drive a FET configured as a switch for a dc load. It can also be used to drive a pair of FETs configured as a switch

for an ac load. See 3. Applications.

2.6 Miller Clamp

2.6.1 Miller Clamp Description

The Si875x devices provide a clamping device to prevent unintended turn on of the external FET when a high dV/dt is present on the

FET’s drain. To use this feature, a capacitor is connected between the drain(s) of the FET(s) and one of the MCAPx inputs. A sudden,

positive slope on this pin will cause the clamp device within the Si875x to activate and provide a low impedance path between the gate

and source pins. This will prevent the FET from being unintentionally turned on.

The Si875x device provides two miller clamp input pins. This allows for both FET’s to be protected from unintended turn on when the

device is used in an AC switch configuration. In this case each drain is connected to an MCAPx input through a capacitor.

Connection to a MCAPx pin, and use of the Miller Clamp feature, is optional. The device will function as expected if these pins are left

unconnected.

2.6.2 Sizing Miller Clamp Capacitors

The recommended value of the capacitor used to connect the drain of the external FET to the Si875x device is typically 10 pf. If the

application has a very large dV/dt and the clamp is not adequately keeping the external FET off, then this capacitor value can be

increased up to 100 pf. The voltage rating of the capacitor should be greater than or equal to the peak voltage expected at the drain

of the FET. The relationship of the capacitor and the dV/dt is governed by the equation: C = IMC/(dV/dt); where: IMC is the Miller Clamp

input current (6mA max, as specified in Electrical Tables), and dV/dt is the expected slew rate.

Si8751/52 Data Sheet • System Overview

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

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206331A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • July 27, 2022

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