EN

Device 1

Overheat

Fan

Driver

Device 2

Overheat

Device 3

Overheat

10

SN74HCS4075

SCLS795A – FEBRUARY 2020 – REVISED JUNE 2020

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Copyright © 2020, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The SN74HCS4075 includes three 3-input OR gates with Schmitt-trigger inputs. These 3-input OR gates work

independently, but can be combined to get up to a 7-input OR gate. It can be used with all three inputs active, or

one input can be disabled by directly connecting it to ground to turn the device into a 2-input OR gate.

The SN74HCS4075 is used to directly control the Enable pin of a fan driver. The fan driver requires only one

input signal to be HIGH before being enabled, and should be disabled in the event that all signals go LOW. The

3-input OR gate function combines the three individual overheat signals into a single active-high enable signal.

Temperature sensors can often be spread throughout a system rather than being in a centralized location. This

would mean longer length traces or wires to pass signals through leading to slower edge transitions. This makes

the SN74HCS4075 ideal for the application since it has Schmitt-trigger inputs that do not have input transition

rate requirements.

9.2 Typical Application

Figure 9. Typical application block diagram

9.2.1 Design Requirements

•

All signals in the system operate at 5 V

•

The fan driver should be enabled if any one or more of these conditions apply:

–

Device 1 overheats

–

Device 2 overheats

–

Device 3 overheats

9.2.1.1 Power Considerations

Ensure the desired supply voltage is within the range specified in the Recommended Operating Conditions. The

supply voltage sets the device's electrical characteristics as described in the Electrical Characteristics.

The supply must be capable of sourcing current equal to the total current to be sourced by all outputs of the

SN74HCS4075 plus the maximum supply current, ICC, listed in the Electrical Characteristics. The logic device

can only source or sink as much current as it is provided at the supply and ground pins, respectively. Be sure not

to exceed the maximum total current through GND or VCC listed in the Absolute Maximum Ratings.