Added on September 27, 2014

Watch a demo of the connections required for current sharing applications of the ZL8801.

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Video Transcript

Hello, my name is Brandon Howell and I handle Technical Marketing with Renesas' Digital Power Group. I'm here to talk about the ZL8801 and how it can support current share. The ZL8801 is a dual phase controller with a fully digital control loop. I've got the eval board right here. This is showing a four-phase design. On the board behind me I show all the important connections that are required for a current share application. I have the ZL8801, our power stages in this case the ISL99140 DrMOS power stage. I have all the outputs connected together and then I have a DDC and sync bus to enable current share operation.

So let me go into some details exactly what DDC and sync mean. The sync bus allows us to synchronize the clocks spreading between the two devices. One of the devices outputs its clock and the other of the devices receives that as an input. This allows us to do phase spreading, to have ripple cancellation in a current share application.

The other bus is the DDC bus. The DDC bus is a Renesas proprietary bus that allows for inter-device communication. Using the DDC bus the controllers are able to broadcast their current share information between each other. We use this bus for a dynamic current balance and it allows the controllers to have equal balance between all four phases. So again in this case I have a four-phase design with the outputs tied together and the ISL99140 DrMOS power stage. A design like this will be capable of approximately 120A.

In the corner here I'm showing what interleave is. So in this case I've got four phases. These will be the four phases, one from each controller and they're all interleaved and separated by 90° increments. By separating the 90° increments you effectively multiply your switching frequency by four. So in a 500kHz per phase application you're looking at an effective switching frequency of 2MHz. This can allow for very low Vout ripple and also helps improve the transient performance.

Now let's go to the lab and we'll take a look at the ZL8801 using our PowerNavigator software and I'll show how easy it is to set up the devices for current share using our GUI software. So the first thing I'll do is show you how you configure the ZL8801 for current share. The ZL8801 eval board by default comes pre-configured, so this is not something you need to do but I'll just go through and show you how easy it is to deal with our GUI.

The first thing I'm going to do is drag the ZL8801 controller from our PowerNavigator part library. So I'll drag two devices on to the power map and then to put them in current share, it's as simple as dragging one of the devices by this donut-looking object. And then when I drag it and drop it on top of the other one, that donut highlights, I let go of the mouse and now I've got a four-phase current share configuration with the ZL8801. If I wanted just the output voltage, for example to 1V, I just type in 1V and then I've got a 1V output. So setting up current share with PowerNavigator is very simple, thanks to the ease of use of the GUI.