STM32H725RGV6 (VFQFPN68): must VCAP be externally connected to the SMPS output / VFBSMPS?
Hi,
I'm finishing a 4-layer board with an STM32H725RGV6 (VFQFPN68). As confirmed in earlier threads, this package has no VDDLDO pin and supports only direct SMPS or bypass, so the core runs in direct SMPS mode.
Current wiring:
- VDDSMPS on 3.3 V, VSSSMPS to ground
- 2.2 µH inductor from VLXSMPS to VFBSMPS, with 2 × 10 µF from that node to ground
- VCAP1, VCAP2, VCAP3: 100 nF to ground at each pin, with no external connection to each other or to the VFBSMPS/inductor node
AN5419 §2.1.7 says that in direct SMPS mode "the SMPS is directly connected to the VCAP pin and provides the regulated supply to the Vcore", and Table 2 says "All VCAP connected together". But the AN never mentions the VFQFPN68, its direct-SMPS figure is marked "Only for LQFP/BGA", and this package already bonds VDDLDO to VDD internally. So I can't tell whether VFBSMPS is also bonded to the core rail inside the VFQFPN68.
Questions:
1. On the VFQFPN68, does the inductor output (VFBSMPS node) need an external copper connection to the VCAP pins, or is VFBSMPS bonded to VCORE internally?
2. Should VCAP1–3 be tied together externally on this package?
3. What capacitance is recommended at VFBSMPS and at each VCAP pin for this package?
4. Is there an ST reference schematic or layout for the VFQFPN68 in direct SMPS mode?
The three VCAP pins are on three different sides of the package, so this decides whether I need a core-supply ring around the chip. That makes the layout really awkward with this particular QFN package, which is why I ask.
Thanks!