Selection of Single-Cell Buck Narrow VDC Switching Battery Chargers

Abstract

This application report provides a general single-cell charge selection guidance and comparison among BQ2419x, BQ2429x, BQ2589x, BQ25898x, BQ2560x, BQ2561x, and BQ2562x single-cell switching battery charge devices with Narrow Voltage DC (NVDC) Power Path Management. The document presents the main differences and describes the key features of each part. The summary also includes the comparison across various charger product families. This information provided hereby can assist design engineers with making good choices for their single-cell switching battery charging applications.

Trademarks

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1 Introduction

Besides the common charger parameters such as the input voltage range, the battery charge voltage limit, the maximum charging current, the package size and so on, a single-cell charger designer needs to consider system-level architecture including but not limit to the input current limit detection scheme, the system control methodology, the system monitoring and protection scheme and boost mode operation.

1.1 Input Current Limit Detection

If the application requires USB D+/D- input current limit detection capability, the user needs to check the related specs of a charger IC. Please visit USB D+ D- Input Current Limit Detection for BQ2419x, BQ2429x, BQ2589x, BQ25898x, BQ2560x, and BQ2561x (USB D+ D- Input Current Limit Detection for BQ2419x, BQ2429x, BQ2589x, BQ25898x, BQ2560x, and BQ2561x application note) for the details.

If the application does not require USB D+/D- input current limit, the user can either leave the D+/D- pins open or short the D+/D- pins together. Below are the general guidelines. Please refer to the corresponding data sheet for the specific input current limit settings

When D+/D- pins are open, the input source is usually detected as Unknown Adapter.
When D+/D- pins are short, the input source is usually detected as USB DCP.

1.2 Control Methodology Host Controlled vs Stand-Alone

As a battery charger designer, one of the most important questions to consider is the control method for the charging system. Shall a microprocessor-controlled charger or a stand-alone charger be used?

The two most popular control methodologies are:

Inter-Integrated Circuit (I2C) controlled: The I2C bus is a very popular and powerful bus used for communication between a host device (or multiple host devices) and a single auxiliary device (or multiple auxiliary devices). A microcontroller, known as the host device, is necessary to communicate with auxiliary devices, including the charger. It’s possible for the host device to modify tens of charger system parameters via I2C on the fly. Charger status as well as fault conditions can be reported back to the host device.
Stand-alone: The charger functions independently without any software or host control. Fixed resistors on the board determine adjustable settings like charge current and voltage limit.

Table 1-1 lists what can be considered when determining the control method for a charger system.

Table 1-1 I2C Control vs. Stand-Alone

	I2C-controlled	Stand-alone
Need real-time control over the charger?	√	X
Need the flexibility of charging parameters?	√	X
Need to monitor charging parameter values?	√	X
Require a host?	Yes	No
Require software code?	Yes	No

1.3 Battery Monitoring and Protection

To improve battery safety, battery monitoring and protection are important in a charger system. The main job of a charger is to charge the battery. The chargers are essentially power supplies with complex state machines and analog feedback loops. In general, chargers do not offer battery monitoring function and only implement basic battery protection functions such as under-voltage protection, over-voltage protection and over-current protection.

The gauges are micro-controllers using ADCs and digital logic. Although a few chargers offer battery monitoring as an extra feature in addition to regular charger, a gauge makes more accurate voltage, current and temperature measurements compared to that of a charger. For accurate ADC measurements and full-featured battery monitoring function, a gauge is recommended.

1.4 Boost Mode On-The-Go (OTG) Output

For the single-cell switching battery charge devices discussed hereby, most of them support boost mode operations while some chargers provide the boost output at both VBUS and PMID pins (Q1 RBFET is on in boost mode) and some chargers provide the boost output at the PMID pin only (Q1 RBFET is off in boost mode). If an application uses the boost mode operations, the charger designer needs to check which pin needs the boost output in their system.

2 Stand-Alone Single-Cell Switching Battery Chargers

Table 2-1 shows available stand-alone single-cell switching battery chargers.

Table 2-1 Device Comparison for Stand-alone Single-Cell Switching Battery Chargers

	BQ25606	BQ25616	BQ25616J
Quiescent battery current (BAT, SYS, SW)	58 µA	9.5 µA	9.5 µA
VBUS OVP Reaction-time	200 ns	130 ns	130 ns
Input voltage regulation accuracy	±3%	±2%	±2%
TS profile	JEITA	Hot/Cold	JEITA
Charge safety timer accuracy	10 hr	20 hr	20 hr
Charge Voltage Limit	4.2 V/4.35 V/4.4 V	4.1 V/4.2 V/4.35 V	4.1 V/4.2 V/4.35 V
Battery voltage regulation	±0.5%	±0.4%	±0.4%
ACDRV	No	Yes	Yes