AMD Chipsets As of Now
If you’d forgotten, AMD originally launched Ryzen with A320, X300, and A/B300 at the low-end. The last 3 might not sound familiar, because they basically stopped getting marketed: You can technically run Ryzen CPUs without a chipset, and the X300 part was targeted toward boards that were intended to be so small that there was no space for a separate chipset component.
The A320 chipset was among the cheapest available to DIY users and has persisted unreplaced until now. You can expect A520 on low-end motherboards, particularly those in the sub-$100 range. These parts will be available through motherboard manufacturers immediately, both to DIY and to OEM markets.