SCLA055 September 2022 SN74AHCT08 , SN74AHCT08Q-Q1 , SN74HCS08 , SN74HCS08-Q1 , SN74LVC08A , SN74LVC08A-Q1

1

Functional Block Diagram

For the purpose of this report, a simplified DC fast charger block diagram is used to illustrate the logic and translation use cases, see Figure 1-1 and Figure 1-2. Each red block has an associated use-case document. Links are provided in Table 1-1 and Table 1-2. For a more complete block diagram, see the Interactive Online end Equipment Reference Diagram for DC Fast Charging Stations.

Figure 1-1 Simplified Block Diagram for DC Fast Chargers Power Section

Logic and Translation Use Cases for Power Section

Each use case is linked to a separate short document that provides additional details including a block diagram, design tips, and part recommendations. The nearest block and use-case identifiers are listed to match up exactly to the use cases shown in the provided simplified block diagram.

Table 1-1 Logic Use Cases

Nearest Block	Use-Case Identifier	Use Case
AC/DC Power Topologies	Separate Voltage Nodes	Separate Digital Voltage Nodes
DC/DC Power Topologies	Enable Gate Drivers	Add Enable to Gate Drivers
Power Board Wired Interface	Redrive Digital Signal	Redrive Digital Signals
Power Board Non-Isolated DC/DC Power Supply	Power Good	Combine Power Good Signals

Table 1-2 Translation Use Cases

Nearest Block	Use-Case Identifier	Use Case
Power Board Self Diagnostics and Monitoring	I2C	Translate Voltages for I2C
Power Board Self Diagnostics and Monitoring	SPI	Translate Voltages for SPI

Figure 1-2 Simplified Block Diagram for DC Fast Chargers Human-Machine Interface Section

Logic and Translation Use Cases for Human-Machine Interface Section

Table 1-3 Logic Use Cases

Nearest Block	Use-Case Identifier	Use Case
Output User Interface	Drive Indicator LED	Drive Indicator LEDs
Input User Interface	Input Expansion	Increase the Number of Inputs on a Microcontroller
Input User Interface	Output Expansion	Increase the Number of Outputs on a Microcontroller

Table 1-4 Translation Use Cases

Nearest Block	Use-Case Identifier	Use Case
Wireless Interface	UART	Translate Voltages for UART

Add Enable to Gate Drivers

It is common to see DC fast chargers include multiple gate drivers. The gate driver can have safety features included, they can be included in software, or an added logic circuit can be used to disable signals when required. By using AND gates, a single input can be used to control many gate drivers, forcing them all into the off state at the same time.

Figure 1-3 Example block diagram to use AND gates to enable gate driver signals

Design Considerations

Open-drain outputs require pull-up resistors
Keep traces relatively short to reduce capacitive loading and improve performance
Easily enable multiple gate drivers through one signal
[FAQ] How do I Calculate Power Consumption for my CMOS Logic Device?
[FAQ] How does a slow or floating input affect a CMOS device?
Need additional assistance? Ask our engineers a question on the TI E2E? Logic Support Forum

Recommended Parts

Part Number	AEC-Q100	V_CC Range	Channels	Features
SN74LVC08A		1.65 V — 3.6 V	4	High Drive Strength - 24 mA
SN74LVC08A-Q1	?	2 V — 3.6 V	4	High Drive Strength - 24 mA
SN74AHCT08		4.5 V — 5.5 V	4	TTL-compatible inputs
SN74AHCT08Q-Q1	?	4.5 V — 5.5 V	4	TTL-compatible inputs
SN74HCS08		2 V — 6 V	4	Schmitt-trigger inputs
SN74HCS08-Q1	?	2 V — 6 V	4	Schmitt-trigger inputs

For more devices, browse through the online parametric tool where you can sort by desired voltage, channel numbers, and other features.