COMPUTE MODULE OPERATING INSTRUCTIONS POWERING THE MODULE The Compute Module has 6 separate supplies that must be present at all times (i.e. they must all be powered, you cannot leave any of them unpowered even if a specific interface or GPIO bank is unused). 1. VBAT is used to power the BCM2835 processor core (it feeds the SMPS that generates the chip core voltage) 2. 3V3 powers various BCM2835 PHYs, IO and the eMMC Flash 3. 1V8 powers various BCM2835 PHYs, IO and SDRAM 4. VDAC powers the composite (TV out) DAC 5. GPIO0-27 VREF powers the GPIO 0-27 IO bank 6. GPIO28-45 VREF powers the GPIO 28-45 IO bank SUPPLY VOLTAGE / VOLTAGE RANGE TOLERANCE VBAT 2.3-5V 1 +/- 5% 3V3 3.3V +/- 5% 1V8 1.8V +/- 5% VDAC 2.5-2.8V (can connect to 3V3 if unused) +/- 5% GPIO0-27 VREF 1.8-3.3V +/- 5% GPIO28-45 VREF 1.8-3.3V +/- 5% 1 **NOTE that the voltage range for best SMPS efficiency is ~3.3-4.3V POWER SEQUENCING Supplies must be synchronised to come up at exactly the same time, or staggered such that the highest voltage comes up first, then the next highest etc. This is to avoid forward biasing internal (on-chip) diodes between supplies and causing latch-up. POWER REQUIREMENTS Exact power requirements will be heavily dependent upon the individual use case. If an on-chip subsystem is unused it is usually in a low power state or completely turned off. For instance if your application does not use 3D graphics then a large part of the core digital logic will never turn on and need power. Similarly for camera / display interfaces, HDMI, USB interfaces, video encode/decode etc. Power chain design is critical for stable and reliable operation of the Compute Module. We strongly recommend that designers spend time measuring and verifying power requirements for their particular use case and application, as well as paying careful attention to power supply sequencing and maximum supply voltage tolerance. The following table gives a r ough guide as to minimum supply requirements. **However, the user is responsible for verifying that their power- chain is designed sufficient for their application. In some more pathological use cases these minimum requirements may well be too low ** SUPPLY MINIMUM REQUIREMENT (MA OR MW) VBAT 2000mW 1 3V3 250mA 1V8 250mA VDAC 25mA GPIO0-27 VREF See note 2 GPIO28-45 VREF See note 2 1 **NOTE VBAT is heavily dependent upon the application. E.g. with video encode, 3D and camera all running the power requirements can be substantial. 2 **NOTE that each GPIO bank will only need a few mW if unused, however when in use the requirements will vary depending on number of IOs in use, and the load on each. The designer is responsible for calculating or measuring this themselves based on their particular use case.MODULE BOOTING / FLASHING THE EMMC The 4GByte eMMC Flash device on the Compute module is directly connected to the primary BCM28235 SD/eMMC interface. These connections are not accessible on the module pins. When initially powered on (or after the RUN pin has been held low and then released) the BCM2835 will try and access the eMMC device and look for a file called bootcode.bin on the primary partition (which must be F AT) to start booting the system. If it cannot access the eMMC device or the boot code cannot be found, it will fall back to waiting for boot code to be written to it over USB (i.e. its USB port is in slave mode waiting to accept boot code from a suitable host). A USB boot tool is available (