This week’s EYE ON NPI (video) stands alone as a fantastic new solution for high power charging of large battery packs and also power boosting from battery to system: it’s ADI/Maxim’s MAX77789 Standalone 3.15A Charger, an all-in-one power management IC that lets you ditch DC power plugs and simplifies your BOM, at an excellent price.
We’ll also be covering the MAX77787 which is the fraternal-twin-sister product: using I2C instead of resistor settings for configuration.
We’ve been covering USB Type C PD sinks and supplies for about a year here on EYE ON NPI & The Great Search, they’re an excellent way to ditch those DC barrel jack power supplies and allow folks to use a single connector and standard power supply for various voltages, from 5V-20V at up to 5A. There’s plenty of chips that will connect to a PD source and negotiate that voltage for you but now we can start to take advantage of USB PD for battery charging as well!
This week’s dynamic duo does pretty much everything for battery management. As devices get more complex, and battery cost goes down, the packs included in products are getting bigger. If you’re trying to charge a 5Ah battery at standard 5V/1A rates, it will take at least 5-8 hours to do so, when folks really want 1-2 hour charge rates.
The MAX77789 and MAX77787 have a buck converter that will deliver up to 3A to the battery for 3x faster charging. But, if you try to draw 3A from a USB 5V power cable, that built-in resistance will cause a voltage droop – remember we need at least 4.5V to have the headroom for charging up to 4.2V or 4.35V Lithium batteries. Thus, these chips use USB PD to request higher voltages when available: 9V or 12V means that we can draw less current to get the same amount of power, which means less resistance loss over the cabling.
For pre-C chargers, such as Samsung or Apple or Quick Charge the USB D+/D- pins are used. In such cases where you want to have the data pins available for USB data/sync, you’ll need something like the MAX20334 data line switch to flip the pins back to your MCU.
The MAX77789 uses resistors on the IFAST, ISET and INLIM lines to set the charge rate, timeout, and pack float voltage, the MAX77787 uses I2C. Both have a couple configuration pins, and LEDs for status monitoring.
Both have the ability to also be turned into a boost converter – you can’t use both charging and boosting at the same time, but since you can use the SYS voltage when connected to USB, you’ll have at least 5V either way. The booster is fixed to 5.1V output. On the ’89 the boost is enabled by GPIO, the ’87 enables it over I2C.
Both chips are available in 0.4mm pitch BGA – which means pad-in-via and multi-layer boards in order to pass the inner configuration traces out. Many of the traces are tripled-or-quadrupled to provide the current carrying capability of 3A charge and 6A peak discharge. An eval board is also available which makes quick verification easy. For the I2C configuration version there’s also desktop software to try out various settings – the standalone version has jumpers so you can attach any resistor value.
Both the ADI/Maxim MAX77789 and MAX77787 Standalone/I2C 3.15A Chargers are in stock right now at DigiKey for immediate shipment. It’s great to see forward momentum in chip design releases now that the shortages have abated: only a year ago we were scrambling for diodes and op-amps and now we have a wealth of great new products to choose from! Order one of these powerful Lithium battery management chips today and you’ll have it shipped immediately so that you can start integrating it into your new design by tomorrow afternoon.
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