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Issue #228 July 2009
LiOn King
A Look at “Battery-in-a-Chip” Technology
by Tom Cantrell
Start | Energy In A Chip | Charge It | UPS-Lite | Dust Storm | Tips & Tricks | Harvest Time | Sources & PDF
CHARGE IT
Recharging an EnerChip battery is simple enough. The easiest approach is simply to connect it to a 4.1-V supply and the battery will fully recharge in less than an hour. Alternatively, a two-phase scheme can be used that starts with a constant current (e.g., 50 µA) phase and finishes with a constant voltage (4.1 V) phase. The documentation notes the two-phase approach may be required for future EnerChips; but for these initial batteries, the single-phase constant voltage approach is fast and easy.[3]
The main consideration is that the 4.1-V supply needs to be rather precise—within a few percentage points (see Figure 3). If the voltage is too high (e.g., 4.3 V), the battery will exhibit “cycle fade,” in which the capacity declines with each recharge cycle. Too low (e.g., 4.0 V) and the battery won’t recharge to full capacity.
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| Figure 3—To recharge an EnerChip, you’ll need a power supply that delivers exactly 4.1 V—no more, no less. The proper charge voltage both maximizes charge capacity while minimizing “cycle fade.” |
The EnerChip internal impedance is high enough that there’s no need for extra components to limit the charge current, at least as long as the charging voltage isn’t too high (i.e., it should not be greater than 4.3 V). As shown in the typical battery-charging profile (see Figure 4), the charge current peaks at about four times the battery capacity (i.e., 48 µA for the CBC012 and 200 µA for the CBC050).
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| Figure 4—While the charge voltage should be precise (e.g., 4.1 V), not much current is required, just 200-µA peak for the 50-µAh CBC050. |
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