bq25071 1-A, Single-Input, Single-Cell LiFePO4 Linear Battery Charger with 50 mA LDO

1 Features

Single Cell LiFePO₄ Charging Algorithm
30V Input Rating, With 10.5 V Overvoltage Protection (OVP)
50mA Integrated Low Dropout Linear Regulator (LDO)
Programmable Charge Current Through ISET and EN Terminals
7% Charge Current Regulation Accuracy
Thermal Regulation and Protection
Soft-Start Feature to Reduce Inrush Current
Battery NTC Monitoring
Charging Status Indication

2 Applications

Smart Phones
Mobile Phones
Portable Media Players
Low Power Handheld Devices

3 Description

The bq25071 is a highly integrated, linear, LiFePO₄ battery charger targeted at space-limited portable applications. It accepts power from either a USB port or AC adapter and charges a single-cell LiFePO₄ battery with up to 1 A of charge current. The 30 V input rating with 10.5 V input overvoltage protection supports low-cost unregulated adapters.

The bq25071 has a single power output that simultaneously charges the battery and powers the system. The input current is programmable from 100 mA up to 1 A using the ISET input or configurable for USB500. There is also a 4.9 V ±10% 50 mA LDO integrated into the IC for supplying low power external circuitry.

The LiFePO₄ charging algorithm removes the current taper typically seen as part of the constant voltage mode control used in Li-Ion battery charge cycles which reduces charge time significantly. Instead, the battery is fast charged to the overcharge voltage and then allowed to relax to a lower float charge voltage threshold. The charger integrates the power stage with the charge current and voltage sense to achieve a high level of accuracy in the current and voltage regulation loops. An internal control loop monitors the IC junction temperature through the charge cycle and reduces the charge current if an internal temperature threshold is exceeded.

Device Information⁽¹⁾

PART NUMBER	PACKAGE	BODY SIZE (NOM)
bq25071	WSON (10)	2.00mm x 3.00mm

For all available packages, see the orderable addendum at the end of the datasheet.

4 Application Schematic

5 Revision History

DATE	REVISION	NOTES
July 2014	*	Initial release.

6 Device Comparison Table

PART NUMBER	V_BAT(OVCH)	V_BAT(FLOAT)	V_(OVP)	V_(LDO)
bq25071DQCR	3.7 V	3.5 V	10.5 V	4.9 V
bq25071DQCT	3.7 V	3.5 V	10.5 V	4.9 V

7 Pin Configuration and Functions

bq25071

(TOP VIEW)

Pin Functions

PIN		I/O	DESCRIPTION
NAME	NO.	I/O	DESCRIPTION
IN	1	I	Input power supply. IN is connected to the external DC supply (AC adapter or USB port). Bypass IN to GND with at least a 0.1 μF ceramic capacitor.
ISET	2	O	Input current programming bias pin. Connect a resistor from ISET to GND to program the input current limit when the user programmable mode is selected by grounding the EN pin. The resistor range is between 1 kΩ and 10 kΩ to set the current between 100 mA and 1 A.
GND	3, 9	–	Ground pin. Connect to the thermal pad and the ground plane of the circuit.
LDO	4	O	LDO output. LDO is regulated to 4.9V and drives up to 50 mA. Bypass LDO to GND with a 0.1 μF ceramic capacitor. LDO is enabled when V_(UVLO) < V_IN < V_(OVP).
TS	5	I	Battery pack NTC monitoring input. Connect a resistor divider from LDO to GND with TS connected to the center tap to set the charge temperature window. The battery pack NTC is connected in parallel with the bottom resistor of the divider. See the Detailed Design Procedure section for details on the selecting the proper component values.
BAT	6	I	BAT is the sense input for the battery voltage. Connect BAT and OUT to the battery.
EN	7	I	Enable input. Drive EN high to disable the IC. Connect EN to GND to place the bq25071 in the user programmable mode using the ISET input where the input current is programmed. Leave EN floating to place the bq25071 in USB500 mode. See the Input Current Limit Control (EN) section for details on using the EN interface.
CHG	8	O	Charge status indicator open-drain output. CHG is pulled low while the device is charging the battery. CHG goes high impedance when the battery is fully charged.
OUT	10	O	System output connection. Bypass the OUT to GND with a 1 μF ceramic capacitor. Connect OUT and BAT together.
Thermal Pad	Pad	–	There is an internal electrical connection between the exposed thermal pad and the GND pin of the device. The thermal pad must be connected to the same potential as the GND pin on the printed circuit board. Do not use the thermal pad as the primary ground input for the device. GND pin must be connected to ground at all times.