How do portable devices use batteries inline with chargers?

Question

I am developing a project that has access to intermittent 0, 9-15 V DC external power, and want to augment that with an on-board battery to cope with multiple hour power outages from the supply. I am drawing less than 1 amp at 9 V from a step-up step-down regulator in the device, however input voltage can vary 7-12 V if necessary. I had imagined using one or several Li-Ion or Li-Po cells to step up to around 12 V, and include a circuit to handle charging the battery when power is available and discharging the battery when not, all while the device is active.

I thought it would be a simple case of putting a battery in line with supply, much like a lead acid battery in a car. However it seems modern batteries need a lot of nursing. I was put on to PMICs however there seem to be such a massive variety of them with different functionalities, I don't know what terminology would describe what I am after.

A belt and suspenders solution I could have the device monitor battery power and shut down gracefully below a level, but that is not absolutely necessary.

What strategies are used to integrate batteries with devices and power supplies, and thus what functionalities do I need to complete the project I have in mind?

I can see many answers to similar questions here, however some appear to accept that either the battery will discharge with no power, or be switched out when power is available, or switched to dedicated charging mode or something clunky like that. I'd like something more graceful.

Answer 1

What you are looking for is called PMIC, "power management IC". Texas instruments has extensive portfolio (~100s) products to fit various needs. (I am less familiar with LT offerings, and they usually are more expensive, and the TC4000 is a good example). NXP and several other IC manufacturers offer similar products. The PMICs are fairly intelligent devices that provide a lot of "services" for system (usually referenced as SYS) power:

1. They check for quality of input power;
2. If power is not present, they provide the SYS power from battery (usually Li-Ion)

3. if external power is available, they provide SYS power directly;

4. If battery is not fully charged, they charge it to pre-set specifications;

5. if SYS consumption and battery charging exceeds the preset limit for external supply, the ICs will scale battery charging down while providing the SYS voltage.
6. they provide full temperature control over chip itself and the managed battery.
7. they provide various optimizations like soft-start, under-voltage and over-voltage protection, etc.

All you need is to learn their terminology and select the IC that suits your particular requirements. Full system management solution usually requires a microprocessor that communicates with PMIC via a serial interface (usually I2C).

Answer 2

I'm not entirely sure what the question is, but a charge controller with something similar to Linears Power Path seems to be what you are looking for. Check LTC 4000-1. TI has similar products. It's able to charge and supply system power at the same time.