SN74HC595B

SN74LVC138A

0V

3.3V

3.3V

0V

SER

SRCLK

RCLK

GPIO Inputs

GPIO Inputs

A

B

C

HIGH

HIGH

HIGH

Y0

Y7

QA

QH

Copyright © 2016, Texas Instruments Incorporated

12

SN54LVC138A, SN74LVC138A

SCAS291W – MARCH 1993 – REVISED OCTOBER 2016

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Product Folder Links: SN54LVC138A SN74LVC138A

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Copyright © 1993–2016, 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 SN74LVC138A is useful as a scanning column selector for an LED Matrix display as it can be used for the

low-side drive of the LED string. The decoder functionality ensures that no more than one output is pulled to a

low-level logic voltage so that only a single column is enabled at any point in time.

9.2 Typical Application

Figure 3. LED Matrix Driver Application

9.2.1 Design Requirements

These devices use CMOS technology and have balanced output drive. Take care to avoid bus contention

because it can drive currents that would exceed maximum limits. The high drive also creates fast edges into light

loads, so routing and load conditions must be considered to prevent ringing.

9.2.2 Detailed Design Procedure

1. Recommended Input Conditions

–

For switch time specifications, see propagation delay times in Switching Characteristics—SN74LVC138A.

–

For input voltage level specifications for control inputs, see VIH and VIL in Recommended Operating

Conditions.

2. Recommended Output Conditions

–

Outputs must not be pulled above VCC or below GND.