2.2 Power Supply Connections (Si8751 Only)

The Si8751 requires a 0.1 µF bypass capacitor between VDD and GND. The capacitor should be placed as close as possible to the

package. To enhance the robustness of a design, the user may also include a 1 µf capacitor for bulk decoupling as well as a resistor

(50–300 Ω) in series with the input if the system is excessively noisy.

2.3 TT Pin Description (Si8751 Only)

The Si8751 provides a pin to control how much current is consumed by the supply when the input pin is logic high. The more current

consumed by the input supply, the faster the output can turn on the external FET. This allows the application designer to optimize the

tradeoff between power consumption and switching time.

Typically, this pin is connected to the supply ground through a resistor. The greater the value of the resistor, the less current is

consumed by the input supply. Values can range from 0 Ω (shorted to ground) to open (TT not connected).

In addition to a resistor, a capacitor, typically 0.1 µf, can be placed in parallel to the resistor. This allows the device to draw more

current to switch the external FET on quickly yet draw less supply current in the steady state. Total power over time is reduced while

maintaining fast switching of the FET.

TT

IN

MCAP1

GATE

SOURCE

IN

VDD

GND

MCAP2

Figure 2.5. Si8751 TT Example

Max Drive

Current

Static Drive

Current

~1/C

t

Figure 2.6. Drive Current vs. Time Using TT with Capacitor

2.4 LED Emulator Input (Si8752 Only)

Figure 2.8. Diode Emulator Model and I-V Curve

The Si8752 uses input current to achieve the development of power across the isolation barrier. Therefore, the more current provided to

the input, the more power is developed on the isolated side of the device. This translates into a faster turn on time of the external FET.

This benefit is limited to an input current of about 15 mA. Beyond that, increasing the input current has little effect on the switching time

of the external FET.

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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