A digital hybrid controller combines the performance of Intersil’s analog R4 control loop with the benefits and flexibility of a digital PMBus interface. They offer industry leading transient performance, require no external compensation components, and are completely configured with pinstrap resistors. An external pinstrap resistor configuration eliminates the need for internal non-volatile memory, allowing these parts to follow a traditional analog design flow that many power engineers are familiar with. The latest version of our PowerNavigator software development tool includes a complete design tool for these products that will assist the user with initial component selection to final schematic generation. In this presentation, we’ll run through the differentiating features of this exciting family or products, discuss target applications, and showcase the available design materials and collateral.
Shown here is a top level diagram of the ISL68200/01. At the heart of this family of controllers is Intersil’s R4 analog modulator, offering industry leading transient performance. Wrapped around this is a PMBus interface, with support for supply telemetry, including VIN, VOUT, load current, and temperature; VOUT on the fly setpoint adjustment; and fault reporting. In the lower left hand corner are the external configuration resistors. A simple resistor divider on each pin sets up all device parameters. These configuration resistors eliminate the need for non-volatile memory, removing the extra step of NVM configuration form the design flow.
The three key differentiating features of the ISL68200 and ISL68201 are:
- Ease of use
- High performance
- PMBus support
Because the controllers are completely configurable with external resistor settings, the need for NVM programming has been removed. This, coupled with the compensation free control loop, makes both the ISL68200 and ISL68201 extremely easy to use. The R4 modulator at the heart of these controllers offers industry leading transient performance, and has built-in light load efficiency modes of operation. These two features combine to make these controllers very high performance. And finally, built-in PMBus support allows the user to read back supply telemetry, including VIN, VOUT, IOUT, and temperature. PMBus can also be used to adjust the VOUT setpoint on the fly.
The ISL6800 and ISL68201 represent two controller versions – the ISL68200 has built in MOSFET drivers for pairing up with external MOSFETs. The ISL68201 has a PWM output for driving DrMOS or driver plus MOSFET integrated power stages, such as Intersil’s ISL99140 DrMOS power stage. Generally, the ISL68200 is a good fit for lower current, sub-25A applications. The ISL68201 is a better fit for high current applications, where the power density of a DrMOS power stage outshines that of a discrete FET design. These controllers support a wide 4.5V to 24V input range, and include an integrated 5V LDO for internal chip bias supply and MOSFET driver voltage. The controllers support a 0.5V to 5.5V output range, with a ±0.5% accurate reference, depending on the output voltage setting. The switching frequency is adjustable from 300kHz to 1.5MHz, allowing the user to optimize their design for efficiency, size or performance. The controllers support the full industrial temperature range of -40 to 85 °C. Built-in light load efficiency modes can be enabled to reduce power loss at light load currents, increasing overall supply efficiency. Intersil’s proprietary R4 modulator provides industry leading transient performance while also being very easy to use. Full pinstrap programmability and the included PMBus interface add design flexibility without complication. Both controllers come in a space saving 4mm x 4mm QFN package.
Shown here is a typical application diagram for the ISL68200 with integrated MOSFET drivers. In this application, inductor DCR current sense is used for both OC protection and PMBus READ_IOUT telemetry. An included NTC thermistor is used to sense the power stage temperature and correct for inductor DCR temperature coefficient, resulting in accurate current sense information across the full temperature range. This controller uses an internal DAC reference, eliminating the need for an external voltage divider. Rounding out the external components are a few supply decoupling caps and external pinstrap resistors.
The ISL68201 typical application diagram is very similar to the ISL68200, with the major change being the interface to the power stage. The ISL68201 uses a PWM interface, replacing the integrated drivers found on the ISL68200. The similarity between products makes switching between the controllers easy, depending on the end user application.
The ISL99140 40A DrMOS power stage comes in a 6mm x 6mm package, and follows the industry standard DrMOS 4.0 footprint. It supports peak efficiency >94%, and is fully compatible with the ISL68201’s PFM light load efficiency mode of operation.
The ISL68200/01 have an industry standard PMBus interface. PMBus provides an easy to use two-wire interface (I2C/SMBus based) that allows users to monitor supply telemetry, including real time input voltage, output voltage, load current, and temperature information. The output voltage setpoint can also be changed on the fly, and fault reporting, such as VOUT OV/UV, output overcurrent and power stage overtemperature, can all be monitored. Using PMBus supply parameters, such as switching frequency, light load efficiency modes and VOUT transition rate can be changed on the fly without the need to use a soldering iron. In applications where PMBus is not required, these pins can be left floating – PMBus communication is an optional feature.
At the heart of the ISL68200/01 is Intersil's proprietary R4 modulator. The R4 modulator, which stands for Rapid Robust Ripple Regulator, is based on a hysteretic current mode topology. It offers an inherently stable control loop with exceptionally high control loop bandwidth. Digital adjustable loop gain is included, allowing the user to optimize transient performance over a wide range of VIN, VOUT and output filter designs. One of the key features of the R4 control loop is the ability to adjust both duty cycle and switching frequency in response to load transients. On the next few slides, we’ll see how this benefit translates into less output capacitance and smaller design size than competitive products. The R4 control loop also sports seamless PFM to PWM transition, meaning it can enter and exit light efficiency modes of operation in a single switching cycle.
Here is a scope shot showcasing R4’s transient response. This scope shot, taken from an ISL68200 demo board, shows VOUT deviation with a 15A load step using an all ceramic output cap design. CH1, the yellow waveform, is the output voltage. CH2, the blue waveform, is the switch node and CH3 is the load step. The take away here is R4 can instantly respond to load transients, temporarily increasing both duty cycle and switching frequency to minimize VOUT deviation. In this example, VOUT deviation is kept to <2.5%, easily meeting the requirements of high-end FPGAs and ASICs which can require VOUT deviation of <3%.
The R4 modulator used in the ISL68200/01 includes optional light load efficiency modes of operation. When enabled, the ISL68200/01 will dynamically scale back the switching frequency as the load current decreases. At light load, this results in a power savings of ~0.72W from a reduction in MOSFET switching loss and inductor AC loss. As load current increases, the ISL68200/01 will automatically switch back to regular PFM mode with no input needed form the end user.
The small controller size of the ISL68200/01, coupled with the high performance of Intersil’s R4 modulator, allows for exceptionally small overall design size. In this example reference design, the full supply, including controller, power stage, inductor, input caps, output caps, and supporting resistors and capacitors, fits in a space saving 13mm x 13mm footprint, giving a total area of 169mm2. For size comparison, a US dime has a diameter of 18mm and total area of 255mm2! As boards become smaller and more dense with ASICs, FPGAs and processors, small overall design size is becoming a critical design requirement.
Shown here are the target applications for the ISL68200/01. These controllers are targeted at anyone who is using an FPGA, ASIC or network processor. Example vendors include Xilinx, Altera, Broadcom, Freescale, and Cavium. As far as end market applications, both controllers make excellent fits in wired infrastructure applications, including routers and switches; wireless infrastructure applications, including base stations; and data center storage applications.
This design example showcases how the ISL68200/01 fit in a Xilinx Kintex or Virtex class FPGA design. For the high current core rail, Intersil offers digital multiphase controllers that make an excellent fit. For the other FPGA auxiliary rails, DDR4 memory rails and system level 3.3V and 5V rails, the ISL68200/01 are excellent solutions.
In this design example, we are showcasing how the ISL68200/01 fit in a typical router or network switch application. Again, the high current core rail is handled by one of Intersil’s multiphase controllers. For auxiliary ASIC rails (I/O, SERDES, etc) and the QSFP optical link modules, the ISL68200/01 controllers are excellent fits. The use of PMBus telemetry in these applications provides not only easy to access debug information during system development, but also real time system level performance metrics.
In this final design example, we showcase how the ISL68200/01 would fit in a data center application. Typical data center applications would be based around an Intel processor – Intersil offers several VR multiphase controllers that meet these requirements. The ISL68200/01, however, can be used to generate the remaining point-of-load voltages from the 12V distributed rail. In this case, one controller is used to generate a 3.3V high current rail, which then feeds several Intersil 2A to 3A integrated FET regulators.
Available Design Tools
From a design tool standpoint, the ISL68200/01 have several options. The latest releases of PowerNavigator, Intersil GUI for all digital power controllers, has a built in design tool, that walks the user through component selection to schematic generation. The ISL68200/01 also have simulation models for Intersil's free simulation software, iSimPE. These simulation models allow the user to simulate time domain transient performance with their chosen output inductor and capacitor filter. Finally, both the ISL68200 and ISL68201 have dedicated demo board designs. These boards are fully compatible with PowerNavigator, and include a built-in load hitter, allowing the end user to thoroughly evaluate controller performance.
Shown here is the PowerNavigator GUI. PowerNavigator supports both online (hardware attached) and offline (no hardware) modes of operation. In offline mode, designs can be quickly mocked up using the built-in PowerMap and device library.
Once a design has been mocked up, double clicking on one of the ISL68200/01 PowerMap icons brings up the Rail Inspector design tool. The first page of the Rail Inspector design tool will ask for basic VIN, VOUT and IOUT requirements.
The second page of the tool will assist with component selection, asking the user for selected MOSFETs, output inductor and output capacitors. Inductor ripple current and peak current are automatically calculated, and the affects of switching frequency on inductor ripple current can quickly be determined.
Next, an efficiency curve is automatically generated based on the selected VIN, VOUT, switching frequency, and components. The peak and full load efficiency is automatically calculated, and the affects on efficiency of changing VIN, VOUT and Fsw can easily be determined, allowing the right trade offs to be made.
Next, Rail Inspector assists the user with pinstrap resistor selection. Using drop-down menus, initial device configuration options are setup, and the corresponding resistors for those settings are displayed. In online mode, with hardware connected, the pinstrap resistor values can be decoded from hardware, showing the default configuration settings for that particular design.
As a final design verification step, a Bode plot and output impedance plot of the design is shown. The Bode plot can be used to determine if the R4 gain parameter is set correctly (bandwidth below ½ the switching frequency, sufficient phase margin) and if the selected output caps will meet the desired transient conditions, Zout below the blue Ztarget line.
Once the design has been finalized, a full schematic is generated. The schematic will reflect the FET, output inductor, output caps, and pinstrap resistor settings selected earlier on in the tool. Using this design tool, you can go from initial VIN/VOUT, selection to a full schematic in under five minutes!
To wrap things up, these controllers are cost effective analog controllers with a digital PMBus interface, offering the performance advantages of Intersil’s R4 control loop with the flexibility of a digital PMBus interface. Both the ISL68200 and ISL68201 offer industry leading transient performance, allowing for dense overall solution sizes and lower total BOM count than competitive products. They can be fully configured with pinstrap resistors, removing the need for NVM. This simplified approach follows an analog design flow familiar to most end users. This, coupled with the built-in PowerNavigator design tool and iSim simulation models, makes these controllers exceptionally easy to use, even for inexperienced design engineers.