Palit Radeon HD 4850 Sonic

Palit Radeon HD 4850 Sonic – PCB Design

Palit's Radeon HD 4850 Sonic features a completely redesigned PCB that, through more efficient use of space, ends up being shorter than the reference card by 18mm at 214mm long.

Overall, the layout is much cleaner than the reference design's and the bill of materials (BOM) will be lower because it uses more standardised components than specialist ones. For example, the Radeon HD 4850's low profile chokes have been replaced with standard chokes that we're more used to seeing on motherboards.

Instead of the two phases for the RV770 GPU on the reference card, Palit has opted for to increase this to three phases to power the GPU.

An increase in the number of phases is generally a good thing, because fewer phases can cause issues with matching the supply and demand for the components being powered. Fewer phases can also mean higher latencies between each MOSFET switch operation (on/off) and it can increase the quiescent current (the current flowing through the circuit when it's not actively switching).


However, Palit has got around this by increasing the number of MOSFETs per choke from two to four, and the number of phases from two to three using a single choke design instead of the dual chokes used on the 4850 reference card. With four MOSFETs per phase, the amount of saturation is reduced and efficiency (per phase) is increased – these are a couple of examples of benefits to the design changes that Palit has made.

The memory, on the other hand, still has just one phase but it has been given three MOSEFTs instead of the two on the reference design – this should help to improve the efficiency a little in scenarios where the memory is putting a lot of stress on the power circuitry.

This end of the board is finished off with an eight-pin PCI-Express connector. At first, this was a curious inclusion because there is no need for this much power to be available to the card – at maximum, AMD quotes the Radeon HD 4850's board power at just 110W and 75W of that will be flowing through the PCI-Express interconnect.


So, the question I'm sure you want to know the answer to is why? Well, it's quite simple really – it's all related to the changes that Palit has made to the card's power circuitry. First of all, the eight-pin PCI-Express interconnect has two more pins available than the now ubiquitous six-pin plug – these aren't allocated to additional power though and are instead just extra ground wires that help to make the power 'cleaner'. Secondly, with more phases, it's important that the power is as clean as it possibly can be – the additional ground wires ensure that this is the case.

One final note about the PCB is the memory that Palit has chosen to use. The reference card uses Qimonda's 1.0ns GDDR3 chips, while the Radeon HD 4850 Sonic uses eight 512Mb Samsung BJ1A 1.0ns DRAMs. We're assuming Palit managed to get a better deal with Samsung through its strong standing as an OEM with huge manufacturing power, making boards for both Nvidia and AMD partners (and itself of course). These are interestingly not covered with a heatsink or heatsinks and are instead passively cooled by the air coming off the main cooler directly above them.