Designing effective power management is a challenging engineering task.
Performance and cost are always important issues.
But now new challenges are emerging.
An ever-increasing number of applications are calling for reliable operation in a wide
variety of shutdown modes and fault conditions.
One of the more recent challenges is the requirement for low standby current.
When the application calls for a portable step-down conversion, a buck converter configuration
is a good choice because of its high efficiency and low part count.
However, getting reliable operation under various design corners and fault conditions
can require additional parts, thus adding to cost and area overhead.
The TPS54232 is a buck converter that addresses all these issues.
It is one of several buck converters available from Texas Instruments' power management product
line.
We'll spend the next few minutes reviewing all of the operational features of TPS54232
to illustrate how it insures reliable operation under a wide variety of conditions.
The TPS54232 has an input voltage range from 3.5 to 28V, and delivers a continuous output
current up to 2 amps.
Its output voltage can be adjusted down to 0.8V. Its switching frequency is preset to
1MHz.
A stand-by current of just 1 micro-amp enables battery-powered operation.
It operates at an efficiency typically exceeding 75%.
And under light load conditions, it uses Eco-Mode to skip unnecessary pulsing for even higher
efficiency.
These characteristics make the TPS54232 ideal for a wide variety of applications such as
consumer equipment, industrial and car audio power supplies, and distributed DC power systems.
To get a thorough understanding of the TPS54232, we'll go through the operation of each functional
block in a typical application.
We start with the input voltage connected directly to the device, and a decoupling capacitor.
During modulation, this voltage is switched internally with an integrated high-side n-channel
FET.
With this typical asynchronous buck configuration, the FET provides switched current to the L-C
filter.
A catch diode conducts the inductor current when the FET is off.
The output voltage is regulated by using a voltage divider to set the sense voltage going
back to the error amplifier.
The divider resistors are chosen to scale the output voltage to an internal 0.8V reference.
The error amplifier is a transconductance amplifier with the output pin accessible so
a compensation network can be added.
The frequency of the pulse-width modulation is set by an internal oscillator with a nominal
value of 1MHz.
During normal operation, the FET is turned on at the start of a cycle.
As the current through the FET rises, it is sensed and compared to the output of the error
amplifier.
Once it crosses this threshold, it turns off the FET for the remainder of the cycle.
A slope compensation network ensures a linear slope on the current ramp even when higher
duty cycles cause the FET current to exponentially level off.
A short circuit on the output voltage can potentially cause excessive inductor current.
The TPS54232 avoids this by monitoring the VSENSE input and proportionally lowering the
switching frequency when the output voltage droops.
A capacitor connected to the slow-start pin is charged by an internal current source,
preventing the output voltage from overshooting during power-up.
The slow start is reset by discharging the capacitor during a shutdown.
A capacitor placed on the boot pin is charged by the internal boot charging circuit.
This ensures that the internal FET will only start switching when the voltage across the
boot capacitor has reached 2.1V.
The enable pin is typically driven with a voltage divider from the input voltage.
This is used to put the device into shutdown when the input voltage reaches an under-voltage
condition.
There is also a thermal shutdown.
The TPS54232 achieves higher efficiency during low-current loads by utilizing a pulse-skipping
Eco-Mode.
During a light load, the output of the error amplifier will drop.
When it drops to 0.5V, it is clamped and FET switching is disabled.
As you can see from this complete set of smart features, the TPS54232 is a reliable buck
converter that responds efficiently to a wide variety of fault conditions.
An important factor with any design is development time.
Development time is not just the time it takes to get the initial circuit running.
Rather, it is when the circuit has been thoroughly tested in all corners of the design and all
the details have been worked out.
Texas Instruments offers several powerful tools that enable extensive verification before
committing your buck converter design to production.
The first is the Switcher Pro Power Supply Design Software.
It gives you everything you need to create, manage and share custom power supply designs.
Another tool is the Evaluation module for the TPS54232.
This fully-assembled circuit board enables you to evaluate the buck convertor shown by
this schematic.
We have seen that the TPS54232 addresses the most important issues faced by power supply
designers.
Its integrated components keep the design simple.
This means less cost and area overhead.
A comprehensive set of features means that it will operate with a high-level of reliability
under a wide variety of conditions.
To get started with your next buck converter design, go to the Texas Instruments website
to download the Power Management Guide, datasheet, application notes, and other free software
tools.