My usual criterion for sourcing components is "if Digi-Key has it, it's safe to use" (as far as sourcing is concerned).
So I went there and did the following query: Keyword: OTG -> 2808 Integrated Circuits (ICs) / Embedded - Microcontrollers -> 2487 In stock -> 613 Core Processor: ARM* -> 235 Voltage - Supply (min): < 2.0 V -> 183 Voltage - Supply (max): >= 3.3 V -> 152 Package / Case: <= 64 pins -> 29 Package / Case: no BGA -> 26 "-> N" indicates the number of hits remaining. At this point, all the chips has >= 64 kB Flash and there were no T&R packagings. I sorted by unit price for 100 units: 1.59 Freescale KL2: MKL24Z64VFM4 M0+ 48 MHz, 32-VFQFN 2.04 Freescale KL2: MKL25Z128VFM4 M0+ 48 MHz, 32-VFQFN 2.15 Freescale KL2: MKL25Z128VFT4 M0+ 48 MHz, 48-VFQFN 2.21 Freescale KL2: MKL25Z128VLH4 M0+ 48 MHz, 64-LQFP 2.55 Freescale K20: MK20DX128VFM5 M4 50 MHz, 32-VFQFN ... more Freescale K20, KL4 ... 6.11 TI Tiva C: TM4C1233D5PMI M4F 80 MHz, 64-LQFP 6.67 STM32F2: STM32F205RCT6 M3 120 MHz, 64-LQFP 7.01 TI Tiva C: TM4C1237E6PMI M4F 80 MHz, 64-LQFP ... more STM and TI chips in 64-LQFP ... So this left three families: Freescale Kinetis, and there especially the KL2 sub-series, then TI Tiva C, and finally STM32F2. The TM4C1233D5PMI seems to have only a USB device [1], so the first suitable TM4C in this list would be the TM4C1237E6PMI. But this isn't correct either, and it would really be the TM4C1237D5PM, with Digi-Key list as non-USB while TI list it as OTG. >From the STM32 family, there's also the STM32F205RBT6, which is currently out of stock. Some of the chips don't have pricing for large volumes. For 1000 units, picking the cheapest with at least 48 pins of each group: MKL25Z128VFT4 USD 2.15 (@100) index 1 STM32F205RBT6 USD 4.46 (@1000) 2.07 TM4C1237D5PMI USD 4.60 (@1000) 2.14 STM32F205RCT6 USD 4.87 (@1000) 2.27 I eliminated chips with 32 pins because my current estimates suggest the device needs around 25 pins already for I/O, and some are invariably "lost" for reset and power, bringing the total number of pins used to at least 33. It may still be possible to sequeeze this into a 32 pin budget but let's see about this later. Characteristics: Chip Core Speed Package Flash RAM Features --------------- ------- ------- ------- ------- ------- ---------------------- MKL25Z128VFT4 M0+ 48 MHz 48-QFN 128 kB 16 kB USB-Reg, ID STM32F205RBT6 M3 120 MHz 64-LQFP 128 kB 68 kB 2 x USB, RNG, SDIO, ID TM4C1237D5PMI M4F 80 MHz 64-LQFP 64 kB 24 kB FPU STM32F205RCT6 M3 120 MHz 64-LQFP 256 kB 100 kB 2 x USB, RNG, SDIO, ID Current consumption at 48 MHz (peripherals off/static) should be around 5 mA for the MKL25Z128VFT4, 10 mA for the STM32F205RBT6, and 24 mA for the TM4C1237D5PMI. The KL2 series has a USB voltage regulator which such a feature is missing in the others. A voltage regulator is particularly attractive for the RF dongle. The MCU in the RF dongle should also be small. As we can see above, the KL2 series has members in 32-QFN packages. The STM32 series has the STM32F103 in 36-QFN which has USB device (not OTG) and up to 128 kB of Flash. So it seems that one could find chips for both types of systems in the same family. The STM32F2 series has a built-in random number generator that produces about 32 Mbps. We also have one in the transceiver at 2 Mbps. The STM32F2 series also contains members that have built-in hardware crypto (DES, 3DES, AES, MD5, SHA1, HMAC), but that doesn't seem overly usefulf or out purposes. KL2 and STM32 have a unique chip ID. I haven't found one in a quick look through the TM4C documentation. >From this comparison, it seems that Freescale KL2 and STM32F2 are the main candidates. The TI chip is slightly more expensive than the STM32F2 but is weak in terms of features and draws a lot of power. It also has an FPU we have no use for. The STM32F2 can run very quickly, but we probably wouldn't want to make use of that, due to power consumption. The STM32F2 series goes up to 1 MB of Flash while the KL2 reaches its limit at 128 kB. All have an RTC, but the KL2 has no separate supply for it. This needs more investigation. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
