Last week we made some VS1005g power performance measurements. Some of the following data is going to end up in future versions of the datasheet. Nevertheless, I thought some of you might be interested in the complete set of measurement data.
Today we start with digital power consumption.
What we measured was VS1005g digital power consumption (CVDD). The figures do not include analog (AVDD) or I/O power (IOVDD). Power consumption has been measured running an MP3 decoder under VSOS 3.11. In this test, the MP3 decoder decodes a 1-second 128 kbit/s 44.1 kHz stereo clip from RAM memory in a loop. This way I/O traffic doesn't come into the measurements. CVDD power consumption includes the processor core, all digital interfaces, as well as the 6.144 MHz upsampling converter and its filters, and the Digital-to-Analog converters. The earphone amplifiers/buffers are not included, as they belong to the AVDD domain, nor any I/O traffic.
Currently VSOS doesn't shut down unneeded hardware blocks of VS1005g. Thus, when the default firmware is used to decode audio, more power is consumed than what is absolutely needed. The idea is that when a product is close to ready, it is possible to have a look at what hardware is necessary and what isn't, then deactivate everything that isn't needed. You can see in the table below how optimization helps.
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128 kbps 44.1 kHz stereo MP3 decoding current, CVDD = 1.67V, XTALI = 12.288 MHz
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Clock Current Description
60.000 MHz 24.4 mA Default firmware, using RF clock to get exactly 60 MHz
61.440 MHz 16.5 mA Same as above, but using PLL clock = 5X XTALI instead of RF clock
61.440 MHz 13.4 mA 5X XTALI clock, all unneeded on-chip peripherals left without power / clock. 45% of power saved!
36.684 MHz 12.0 mA 3X XTALI clock, over 50% power savings!
30.720 MHz 11.6 mA 2.5X XTALI clock, would be just enough for 320 kbps MP3
24.576 MHz 11.1 mA 2X XTALI clock, enough for 128 kbps MP3
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Low-samplerate low-bitrate decoding current, CVDD = 1.67V, XTALI = 12.288 MHz
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Clock Current Description
12.288 MHz 7.4 mA XTALI clock, 96 kbps 16 kHz stereo MP3
6.144 MHz 3.8 mA XTALI/2 clock, 56 kbps 16 kHz mono MP3
0.012 MHz 0.1 mA XTALI/1024 clock, running busy loop (Note: need to turn analog out off)
It should be noted that VS1005g's power consumption is quite dynamic. If the CPU does little or nothing, less power is consumed. Compare the MP3 decoding figures above to the situation below, where the processor is running, but idle over 95% of the time:
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No decoding, CPU idle for > 95% of time, CVDD = 1.67V, XTALI = 12.288 MHz
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Clock Current Description
61.440 MHz 7.1 mA 5X XTALI clock
36.684 MHz 5.5 mA 3X XTALI clock
30.720 MHz 5.1 mA 2.5X XTALI clock
24.576 MHz 4.6 mA 2X XTALI clock
12.288 MHz 3.0 mA XTALI clock
6.144 MHz 1.6 mA XTALI/2 clock
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128 kbps 44.1 kHz stereo MP3 decoding current at 24.576 MHz, XTALI = 12.288 MHz
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Voltage Current Description
1.67 V 11.1 mA Inside official limits for sull speed
1.52 V 10.0 mA Not inside official specs, but almost certainly works with 2X clock at all temperatures
1.47 V 9.6 mA A voltage with somewhat more risk
1.42 V 9.3 mA A voltage with even more risk