Xinwen Xinshi丨The last umbrella of protection in the power era, Renesas ISL81X01 series buck-boost controller

In critical application areas such as telecommunications systems, Internet systems, or medical process control systems, any instantaneous failure of the system power supply may lead to unimaginable serious consequences. In order to cope with such emergencies, we generally use backup power systems to ensure that critical equipment can maintain normal operation during power outages.

Battery technology, as the core of the backup power system, has made great progress in recent years. Today, lithium batteries and supercapacitors, as the two main energy storage devices, are gradually becoming popular in modern society. Compared with traditional battery technology, the new energy storage devices are small and flexible, and the charging configuration is simple, which has brought a new development to the application of backup power systems.

Backup power systems are gradually extending from traditional key application areas such as medical systems and industrial systems to non-traditional application areas such as automobiles, outdoor power supplies, and smart street lights. In today's society, we can easily find backup power systems in every aspect of maintaining social operation.

For common DC backup power systems, charging and discharging are the most critical links, that is, electronic devices perform charging and discharging operations from DC power supplies, so that battery power can be quickly transmitted to the system after the main power supply is lost. However, during the charging and discharging conversion process, the problem of intermittent power output has become the crux of the backup power system.

The boost and buck of the charging circuit in the DC backup power system depends on the power supply and battery voltage, while the discharge circuit itself generally uses a buck converter to power the load by converting the battery voltage to the voltage required by the system. For important circuit equipment, short-term power supply interruptions often cause great safety hazards. How to achieve zero-delay connection between system charging and discharging and ensure uninterrupted power, that is, the so-called DC-UPS (battery uninterruptible power supply) function has become the top priority of the DC backup power system.

To solve this problem, we can use the zero-delay conversion feature of charging and discharging in bidirectional circuits to achieve uninterrupted operation of the system and make the system more reliable.

What kind of changes can the bidirectional buck-boost controller solution bring to our DC backup power system? For the circuit itself, the existence of the bidirectional buck-boost controller can combine the complex charging and discharging architecture into one, greatly enhancing the overall reliability of the circuit itself while simplifying the design.

Using a bidirectional buck-boost controller solution, the same set of electronic devices can change the direction of its current for charging and discharging operations, and its proprietary control strategy can ensure minimal interference during transient changes in line voltage or load. At the same time, the system can also discharge the battery more deeply when necessary, which greatly improves the battery capacity utilization.

Next, let’s talk in detail about the core of realizing bidirectional circuits, the Renesas ISL81X01 series buck-boost controller.

The Renesas ISL81X01 product series is a new bidirectional four-switch synchronous boost and buck controller series launched by Renesas Electronics. There are currently 3 products, including ISL81601, ISL81401, and ISL81401A. The Renesas ISDL81X01 product series is also the industry's only two-wire controller series that can detect peak circuits at both ends and provide bidirectional cycle-by-cycle circuit limiting in buck or boost mode. This series of products has a proprietary modulation scheme with small ripple and smooth conversion, voltage and current feedback loop control, and supports buck-boost mode and instant setting change function, which can complete the load point (POL) and voltage rail conversion with a peak efficiency of 99%.

The ISL81601 uses an 8V drive voltage, has a wide input range of 4.5V to 60V, and can generate an output of 0.8V to 60V. The ISL81401 uses a 5.3V drive voltage, has an input range of 4.5V to 40V, and can generate an output of 0.8V to 40V. At the same time, Renesas also provides a unidirectional version of the ISL81401 - the ISL81401A. The ISL81X01 product series has a wide switching frequency setting range of 100kHz to 600kHz and a MOSFET driver with adaptive shoot-through protection function.

Simplify backup systems with Renesas solutions

Renesas Electronics' ISL81601/ISL81401 product series uses a dedicated architecture with two current monitoring pins to monitor the input and output currents for constant current (CC) and constant voltage (CV) control and other system management functions. This architectural design can provide extremely strong protection capabilities and effectively prevent any faults on either side of the system during actual applications. At the same time, the ISL81601/ISL81401 product series uses four independent control loops to control the input voltage, output voltage, input current, and output current. This design is very suitable for DC backup power systems with different charging and discharging rates.

The bidirectional peak current sensing function of the ISL81601 /ISL81401 product family eliminates the complex external circuitry required to charge and discharge the load-powered battery. Its proprietary control strategy provides smooth mode switching between buck, boost, and buck-boost, while reducing low-frequency ripple at Vout, ensuring minimal interference during transient changes in line voltage or load. The control strategy also ensures controllable ripple voltage under all conditions. The addition of multi-layer overcurrent protection and precision control strategy allows the controller to provide constant current output when Vout is as low as 0.8V, thereby achieving reliable operation.

Designers can easily scale system power by paralleling an unlimited number of controllers. The control strategy of the ISL81601 and ISL81401 four-switch controllers ensures that only two switches are operating at high frequency at the same time, minimizing power dissipation and achieving higher efficiency.

ISL81X01 Series Control Algorithm Diagram

At the same time, in terms of circuit safety, Renesas Electronics' ISL81X01 product series has comprehensive multiple protection functions such as undervoltage, overcurrent, and overheating. The peak current sensing and cycle-by-cycle current limiting functions at both ends can ensure that the circuit can perform instant current limiting under fast transient conditions at the input and output ends, thereby ensuring the high reliability of system operation. In addition, when the system is running at a constant current, the output voltage can be reduced to a very low state to avoid possible loss of control under overload and short circuit conditions.

* The article is reproduced from China Electronics Network

To learn more about Renesas Electronics products, click on the mini program below to start learning!