SI8751 Datasheet, PDF (5/27 Pages) Silicon Laboratories – Digital CMOS input option

2.1 Device Behavior
The following are truth tables for the Si875x family.
Table 2.1. Si8751 Truth Table
Si8751/52 Data Sheet
System Overview
VDD
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IN
H
L
X
Table 2.2. Si8752 Truth Table
Gate
H
L
L
Input Current
> I_f(TH)
< I_f(TH)
Gate
H
L
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 con-
sumed 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 maintain-
ing fast switching of the FET.
VDD
Max Drive
Current
MCAP1
TT
IN
GND
GATE
SOURCE
MCAP2
Figure 2.5. Si8751 TT Example
Static Drive
Current
~1/C
t
Figure 2.6. Drive Current vs. Time Using TT with Capacitor
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