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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
UPS-LITE
Cymbet takes their EnerChip technology a major step further with the so-called “CC” upgrade that combines the battery with power-management logic and packs a complete mini-me Uninterruptable Power Source (UPS) in a chip that’s just slightly larger than the battery alone.
EnerChip CCs are available using either the 50-µAh (CBC3150) or 12-µAh (CBC3112) batteries. They’re packaged in a 9 mm × 9 mm 20-pin package, but as shown in Figure 5, there are really only a few pins to deal with.
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| Figure 5—The EnerChip “Charge Controller” parts combine an EnerChip battery and charge control electronics in a single chip. |
With a wide 2.5- to 5-V input range, VDD is the primary power source for the EnerChip CC, just as wall power is the primary source for a 120-VAC UPS. VBAT is directly connected to the battery. VOUT is the uninterruptable 3.3-V (typical) output to the load.
An internal charge pump (with an external capacitor connected to the CP and CN pins) generates a precise 4.1 V on the VCHG pin to charge the battery. It’s simply a matter of connecting the VCHG and VBAT pins to close the loop. If you’re wondering why Cymbet didn’t just connect them for you internally, the answer is that a single EnerChip CC can work with up to 10 external EnerChip batteries for applications that need higher current and capacity than the on-chip battery provides. While it doesn’t hurt the battery to charge it all the time, needless charging consumes power to keep the charge pump running, so the ENABLE (EN) pin provides an external On/Off switch.
The EnerChip CC automatically handles the switchover between primary (VDD pin) and back-up (VBAT) power delivery, the threshold being set with the VMODE pin. If VMODE is connected to VDD, the threshold is 4.5 V (i.e., suitable for 5-V designs). If VMODE is grounded, the threshold is 3.0 V (i.e., for 3.3-V designs). A third option requires a pair of external resistors, the ratio between them setting the threshold voltage anywhere between 2.5 and 5 V. The RESET* pin is driven low when the EnerChip CC is providing power to VOUT from the internal battery.
Battery-protection is also built-in, with the output (VOUT) automatically disconnected from the battery when VBAT falls too low. The combination of precise charge voltage and battery protection maximizes the capacity and number of recharge cycles the battery delivers.
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| Photo 1—The CBC-EVAL-05 includes both 50-µAh (CBC3150) and 12-µAh (CBC3112) EnerChips. It’s easy to switch between one or the other just by rotating the module. |
Cymbet offers some handy evaluation modules that make it easy to experiment and prototype with EnerChip batteries and CC controllers. Consider the CBC-EVAL-05 (see Photo 1), which includes both a CBC3112 and a CBC3150 packaged in a 24-pin DIP format. Notice on the pinout (see Figure 6) how the left and right sides of the DIP are mirror images. One side connects to the CBC3112 and the other the CBC3150 so you can test either by simply rotating the module.
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| Figure 6—The CBC-EVAL-05 module makes it easy to experiment with Cymbet EnerChip technology. |
The module has the flexibility to support a variety of experiments. For instance, if you’re mainly interested in playing with the batteries, but not Cymbet’s charge controller, just leave the VCHG pin disconnected from the VBAT pin and have at it.
There’s also a hybrid option that has one CC, pardon the pun, in charge of the other’s battery (i.e., CBC3150 charge controlling the CBC3112 battery and vice versa). A variation runs both CBCs simultaneously by connecting their VBAT pins with either VCHG pin (not both).
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