BQ24273 Datasheet, PDF (9/27 Pages) Texas Instruments – 2.5A, Single Input, Single Cell Switchmode Li-Ion Battery Charger with Integrated Current Sense

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bq24273
SLUSB08 – JUNE 2012
DETAILED DESCRIPTION
The bq24273 is a highly integrated synchronous switch-mode charger featuring integrated MOSFETs and current
sense element reducing the count of external components. It is targeted at portable applications with higher
capacity batterires powered by 1-cell Li-Ion, LiFePO4 or Li-polymer battery pack. Due to the high efficiency in a
wide range of the input voltage and battery voltage, the switching mode charger is a good choice for high speed
charging with less power loss and better thermal management.
The bq24273 has two operation states: charge state and high impedance state. In the charge state, the bq24273
supports a precision Li-ion, LiFePO4 or Li-polymer charging system for single-cell applications. In the high
impedance state, the bq24273 stops charging and operates in a mode with very low current from IN and battery,
to effectively reduce the power consumption when the portable device is in standby mode.
The bq24273 includes an integrated 35mΩ sense resistor that is used to measure the charge current into the
battery. As resistors are expected to have a temperature coefficient, the bq24273 includes a compensation
mechanism that maintains the accuracy of the charge current as the temperature changes. This allows for a
smaller BOM solution allowing the removal of an external high accuracy sense resistor that are typically needed
for non-power path charger solutions.
Charge Mode Operation
Charge Profile
There are 5 loops that influence the charge current; constant current loop (CC), constant voltage loop (CV),
thermal regulation loop, input current sense loop and input voltage dynamic power management loop (VIN-DPM).
During the charging process, all five loops are enabled and the one that is dominate takes control. The bq24273
supports a precision LiFePO4, Li-Ion or Li-Polymer charging systems for single-cell applications. Figure 2 shows
a typical charge profile.
Precharge
Phase
Regulation
Voltage
Regulation
Current
Current Regulation
Phase
Voltage Regulation
Phase
Precharge
Phase
Regulation
Voltage
Current Regulation
Phase
Voltage Regulation
Phase
V_SHORT
Charge Voltage
V_SHORT
Charge Voltage
Termination
I_SHORT
Precharge
(Linear Charge)
Charge Current
Termination
Charge Current
Fast Charge
(PWM Charge)
(a) Not input current limited
I_SHORT
Precharge
(Linear Charge)
Fast Charge
(PWM Charge)
(b) Input current limited
Figure 2. Typical Charging Profile of bq24273
PWM Controller in Charge Mode
The bq24273 provides an integrated, fixed-frequency 1.5MHz voltage-mode controller to supply the charge
current. The voltage loop is internally compensated and provides enough phase margin for stable operation,
allowing the use of small ceramic capacitors with very low ESR.
The input is protected from short circuit by a cycle-by-cycle current limit that is sensed through the high-side
MOSFET. The threshold is set to a nominal 5-A peak current. The input also utilizes an input current limit that
limits the current from the power source.
Copyright © 2012, Texas Instruments Incorporated
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