PG

ON/OFF

RESET

Power Supply

Motor Controller

On/Off Switch

Over

Current

Detection

OC

9

SN74HCS11

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SCLS790A – JANUARY 2020 – REVISED JUNE 2020

Product Folder Links: SN74HCS11

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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 SN74HCS11 includes three 3-input AND gates with Schmitt-trigger inputs. These 3-input AND gates work

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

or one input can be disabled by directly connecting them to VCC to turn the device into a 2-input AND gate.

The SN74HCS11 is used to control the RESET pin of a motor controller. This system requires three input signals

to all be HIGH before the controller is enabled, and should be disabled in the event that any one signal goes

LOW. The 3-input AND gate combines the 3 individual reset signals into a single active-low reset signal.

Many power good signals utilize open-drain outputs which can produce slow input transition rates when they

transition from LOW to Hi-Z mode. This makes the SN74HCS11 ideal for the application because 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 motor controller should be disabled if any of these conditions apply:

–

Power Supply is not ready (PG)

–

Excessive current is detected (OC)

–

The power switch is in the OFF position (ON/OFF)

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

SN74HCS11 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.

The SN74HCS11 can drive a load with a total capacitance less than or equal to 50 pF connected to a high-

impedance CMOS input while still meeting all of the datasheet specifications. Larger capacitive loads can be

applied, however it is not recommended to exceed 70 pF.