Originally Posted by archro
Hello Jseaber, the C5 is a really good AMP, but I am still have a question about how the C5 power management works?
since the one cell Li Battery is the only power resource so you have to boost it from 4.2v to 14V （+/-7V) could you mind do some introduce about this part or and what kind of IC can been use in a really small PCB area.
and when the battery voltage drop, does the positive and negative voltage still in balance or even the positive/negative always keep in +/-7V?
very appreciate if you can share some knowledge to me.
Great question. The power stage is more than a single chip. Supply voltage to the opamps is always +/-7V. As the battery drains, the circuits compensate to maintain desired voltage. This means current consumption at the battery increases as the battery gets low, and you always hear maximum performance. Here's a C5 flow diagram that lived on our whiteboard for months:
We increased all 7V lines to 8V, and all 6V lines to 7V. The concept remains the same:
Li-Ion Battery --> Charging and Load Management IC (BQ24075) --> Positive and Inversion Boost IC (LT3471) --> Ultralow-noise LDO's --> Dual supply output
As you can judge from this flow diagram, the majority of C5's schematic consists of power circuitry. I've shared this with a few engineers. The first response was, "That's complicated." Another wanted to see FFT's, fearing the 1.2MHz boost/inversion stage would emit EMI/RF and make its way into the opamp output. He was pleased to see the result. Careful layout on the 4-layer PCB gives nice, clean FFT's (no harmonics!):
Output of C5 - 1kHz test signal (time-domain)
Output of C5 - 1kHz test signal (frequency-domain at 1.25kHz intervals)
Output of C5 - 1kHz test signal (frequency-domain at 50kHz intervals)
Edited by jseaber - 4/12/13 at 7:52am