8A, Low Quiescent Current, High Efficiency Synchronous Buck Regulator
Hello and welcome to the ISL8018 8A high efficiency buck regulator training.
Intersil Integrated Switching Regulators
Let’s start by taking a look at the key value propositions of Intersil’s integrated FET switching regulators.
- High level of integration: These ICs integrate PWM control, drivers and the power FETs/switches in one small package, hence enabling high power density. Furthermore, some of Intersil’s integrated FET regulators integrate various value-added features such as power-good, enable, start-up tracking, and frequency synchronization (to external clock). These features can eliminate the need for discrete ICs,such as monitors and sequencers, and provide a complete point of load (POL) power management solution at a lower cost. Intersil’s portfolio also includes dual and triple output regulators that help address the power requirements of multi-POL systems or applications.
- Different switching frequency options: The large portfolio provides various frequency options to optimize designs. Low switching frequency solutions provide higher efficiency, whereas higher frequency solutions provide the advantage of a small overall design footprint. Many devices have adjustable switching frequencies for greater flexibility.
- Various output current choices: Intersil’s switching regulators family has an extensive offering for various load current requirements with solutions optimized for load requirements as low as 150mA to as high as 10A.
ISL8018: High Efficiency 8A Internal FET Buck Regulator
The ISL8018 is Intersil’s latest 5V switching regulator; it supports a continuous load of up to 8A. It accepts an input voltage of 2.7V to 5.5V and can provide an output voltage of 0.6V to VIN, thanks to the ability to run in 100% duty cycle mode. It has outstanding efficiency of up to 97% and can maintain high efficiency even at low loads thanks to the pulse frequency mode (PFM) for light load operation. In addition to more common features like synchronization to external clock and power-good/enable, the ISL8018 integrates some differentiating features that provide significant value added.
First, it provides bidirectional SYNC to eliminate the need for a system clock to synchronize multiple ICs to the same frequency, in order to reduce or eliminate beat frequency. Furthermore, it has programmable phase-shift and a programmable current limit; this provides the benefit of over current protection (OCP) even while operating at lighter loads compared to the rated 8A capability of the IC, which is key to proliferating the IC for various POLs in a particular system and/or various different systems with varying load requirements. The ISL8018 also has a negative current limit to improve reliability.
The ISL8018 also provides output voltage margining, which integrates the ability to margin the output voltage by ±10% to help check for overall system robustness. The adjustable switching frequency from 500kHz to 4MHz allows a trade-off between high efficiency and extremely small filter size. Finally, adjustable soft-start and start-up in pre-biased load provides the customer/application with complete control for a monotonic start-up.
ISL8018 Block Diagram
This is the block diagram of the ISL8018. When FS is connected to VIN, the loop is internally compensated to meet the needs of most applications and the switching frequency is set to 1MHz. The output voltage can be margined by + or – 10% using VSET. This feature is valuable for compensating the IR dropped due to far away system load by increasing the voltage up 10%. VSET can be lowered by 10% to reduce system power dissipation. In addition to these features, the output current can be adjusted to 3A, 5A or 8A using ISET pin.
In an application with two or more ISL8018s, use the SYNCOUT pin to allow the channels to run at the same frequency and out-of-phase. By adjusting the SYNCIN capacitor of the slave IC (in this case C7), adjustable phase-shift delay is achieved.
How Programmable Phase-Shift Work
Here is the timing sequence of the phase delay. The SYNCOUT feature of the master IC turns on a 250uA current source at the beginning of its clock cycle and charges up C7. As the voltage rises to 0.7V, the SYNCIN of the slave IC starts its ON pulse. By changing the value of C7, timing can be delayed. If there are more ICs, then the SYNCOUT of the 2nd IC can drive the 3rd and so on.
One big benefit of operating in an out-of-phase system is input current ripple is minimized. If we compare three converters operating in-phase, the peak input current would be 24A or 12ARMS at 50% duty cycle. On the other hand, an out-of-phase system would have an 8A peak or 4.3A at 50% duty cycle. Thus, significantly reducing the input capacitor requirements and EMI spectrum.
Helpful Design Resources
Several tools are available to aid in designing with the ISL8018. Along with the datasheet and app notes, two boards are available as well as iSim.
ISL8018EVAL3Z Evaluation Board
The ISL8018EVAL3Z is an evaluation board that can be checked in the lab for efficiency and all other features highlighted previously. It is designed for full feature testing, and as such includes additional components that need not be in a final design.
ISL8018DEMO1Z Demo Board
On the other hand, the ISL8018DEMO1Z is a compact 8A demo board that demonstrates a small form factor to fit most applications or quickly connected to another board in a system. The solution size is 0.64” x 0.28”.
How to Access ISL8018 on iSim Online
To access the iSim model online, find the ISL8018 simulation model in the documents tab of the product landing page. You can also find the device in the parametric search table and click on the iSim logo in the far right column.
Designing the Circuit in iSim
Once the part is selected, enter the desired input voltage, output voltage and output current. Click on the Design button and a schematic with typical component values will be generated. Alternately, select custom design to specify the input and output capacitors and the inductor.
The iSim model allows a customer to incorporate the ISL8018 into a simulated design to test circuit functionality before prototyping, and to observe AC analysis, transient responses and start-up times in the system. Tabs along the side allow adjustments to the efficiency and compensation, as well as providing a bill of materials. The design can also be downloaded and used with the offline tool, iSim PE.
Single Output Switching Regulator Product Portfolio
Intersil has a large portfolio of over 80 single output switching regulators optimized for various load currents and input voltage requirements. This graph captures a selection of these devices. The X-axis indicates the input voltage range supported by the products and the Y-axis indicates the rated output current capabilities.
The 5V family of regulators, which includes the ISL8009A, ISL80030 and ISL8018, support maximum load currents from 1.5A to 8A.
The 12V/24V single output product portfolio includes products such as the ISL85001, ISL85003 and ISL8505 that support maximum load currents from 1A to 5A.
We also offer solutions that support voltage inputs of up to 40V and 60V. These include the ISL8540 and the ISL85403 for 40V, and the ISL8560 for 60V.
Multi-Output Switching Regulator Product Portfolio
There are numerous multi-output switching regulators as well. The strategy behind developing a family of multi-output regulators is to complement our portfolio of single output solutions for applications/systems that have more than one point of load.
The availability of dual and triple output solutions enables the customer to optimize their design for lower overall system cost, as well as smaller overall system form factor, compared to using multiple single output solutions.
Intersil’s multi-output family consists of various products that support a wide range of load currents from 800mA to 6A, and a wide VIN range with solutions supporting <5V, 12V/24V and 28V input supplies.
As can be noted from several of these devices, some applications may require an additional low dropout regulator (LDO). Intersil has a large portfolio of LDOs as well.
In summary, the ISL8018 is an 8A highly integrated synchronous buck regulator that provides high efficiency and a wide range for the switching frequency. Its bidirectional synchronization with programmable phase-shift reduces ripple current and noise in the system, while the selectable output current limit and output voltage margining can be adjusted depending on the needs of the application.