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Keywords:
digital output driver, industrial process control, PLC, industrial automation, building automation, inductive loads
APPLICATION NOTE 6339
DIGITAL OUTPUT DRIVERS: UNDERSTANDING KEY FEATURES
AND CHALLENGES
By:
Yuriy Kurtsevoy, Sr. Strategic Applications Engineer
Abstract: This application note explains key features of the MAX14912/MAX14913 octal digital output driver and how they can be utilized in
Industrial and Building Automation Applications.
Introduction
Digital output drivers are widely used in industrial applications for process control (PLC systems) and building automation. They also can be used
anywhere a 24V DC system is used for control such as for motor control, robotics, and machinery automation.
At first look, the digital output driver is a simple device with only two output states: ON or OFF. On closer inspection, designers successfully
replaced mechanical switches and relays providing engineers with many benefits like robust operation, low-power consumption, simplicity, smaller
size, flexibility, and programmability to build automated, fault-tolerant control systems.
Maxim’s digital output drivers features up to 200kHz switching rates, fast and safe inductive load demagnetization, open load, low- and under-
voltage detection, overcurrent and over-temperature protection, watchdog timer, and SPI error detection. They can withstand up to 60V power
spikes, are immune to ±1kV surge pulses and up to 12kV ESD impact, and operate across a wide operating temperature range from -40°C to
+125°C.
In this application note, we discuss how to effectively utilize different features of the
MAX14912/MAX14913 output drivers. To do this, we look at the
decisions a system designer must take and look at the trade-offs and benefits the MAX14912/MAX14913 provides.
Determine System Operating Conditions
High Side (HS) or Push Pull (PP)?
Usually the push-pull operation is used for high-speed communication, where the signal waveform should have sharp edges. The drawback of this
mode is the output is always active, either high or low, and cannot be tristate or have high impedance, unless the Global EN pin is used.
High-side operation, instead, allows the engineer to put the output into a high-impedance state, but the signal waveform is largely dependent on the
load impedance. The outputs can also be connected in parallel allowing larger loads up to 9.6A in high-side mode.
Therefore, selecting the operating mode depends on the particular application.
Power Supply Requirement
The MAX14912/MAX14913 supports a wide range of power supplies from 12V to 36V, that allows them to be used in a wide range of applications,
even in systems with power supply requirements that are less regulated and more tolerant. This guarantees robustness and flexibility of the system
design.
An integrated 5V DC-DC converter eliminates additional power rails, minimizes the number of external components, and increases the system
efficiency. Other devices in the system can be powered from this 5V DC source, which can provide more than 100mA of current to the external
circuits.
System Integration
The digital output drivers are the interface between low-voltage MCUs/FPGAs and relatively high-voltage (12V to 36V) peripheral devices, such as
actuators, motors, lamps, relays, LEDs, etc. They provide high immunity to the voltage and current spikes, inductive or capacitive loads, and
magnetic interference and static discharges.
In addition, the MAX14912/MAX14913 provide extensive diagnostic capabilities including thermal shutdown, open-wire detection, low-supply and
undervoltage detection, and overvoltage and overcurrent protection. The 4 × 4 LED-driver crossbar matrix allows indication per channel for output
status and fault conditions.
Digital Interface
There are two interfaces supported by the MAX14912 and MAX14913; parallel and serial. The system designer has flexibility to use either parallel or
serial interface to control the operation, or to use both interfaces. To understand the interfaces, we first review a few of the global configuration pins.
Global Configuration Pins
EN – driving this pin high enables normal operation of the device; driving this pin low disables any output operation, i.e. makes all outputs high-
impedance.
SRIAL – driving this pin high enables serial (SPI) operation; driving this pin low enables parallel operation.
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