Texas Instruments Evaluation Module for BQ25070 1A, Single cell, Linear Charger for LiFePO4 Applications BQ25070EVM-740 BQ25070EVM-740 Datenbogen
Produktcode
BQ25070EVM-740
Introduction
1
Introduction
The bq25070 is a highly integrated LiFePO
4
linear battery charger targeted at space-limited portable
applications. It operates from either a USB port or AC Adapter and charges a single-cell LiFePO
4
battery
with up to 1 A of charge current. The 30 V maximum input voltage rating with 10.5 V input overvoltage
protections supports low-cost unregulated adapters.
protections supports low-cost unregulated adapters.
The bq25070 has a single power output that charges the battery and powers the system. The charge
current is programmable up to 1 A using the CTRL input. Additionally, a 4.9 V
current is programmable up to 1 A using the CTRL input. Additionally, a 4.9 V
±
10% 50 mA LDO is
integrated into the IC for supplying low power external circuitry.
The LiFePO
4
charging algorithm removes the constant voltage mode control usually present in Li-Ion
battery charge cycles. Instead, the battery is fast-charged to the overcharge voltage and then allowed to
relax to a lower float charge voltage threshold. The removal of the constant voltage control reduces
charge time significantly. During the charge cycle, an internal control loop monitors the IC junction
temperature and reduces the charge current if an internal temperature threshold is exceeded. The charger
power stage and charge current sense functions are fully integrated. The charger function has high
accuracy current and voltage regulation loops, and charge status display.
relax to a lower float charge voltage threshold. The removal of the constant voltage control reduces
charge time significantly. During the charge cycle, an internal control loop monitors the IC junction
temperature and reduces the charge current if an internal temperature threshold is exceeded. The charger
power stage and charge current sense functions are fully integrated. The charger function has high
accuracy current and voltage regulation loops, and charge status display.
2
Considerations With Evaluating the bq25070
Read the complete data sheet (
) to fully understand detailed information that may be useful in
operating and evaluating this EVM.
This EVM can be used as a stand alone evaluation module using the hardware, on sheet 2 of the EVM
schematic, that generates the pulses to program the IC
schematic, that generates the pulses to program the IC
’
s CTRL pin. Placing a single shunt on JP101
through JP113 programs the hardware to deliver pulses via JP3 to the CTRL pin on the IC. Toggling
switch S101 from the down position up then back down sends the programmed pulses to the IC via JP3, if
the input power is present. Potentiometer, R109, can be used to adjust the width of the pulse if it is out of
specification.
switch S101 from the down position up then back down sends the programmed pulses to the IC via JP3, if
the input power is present. Potentiometer, R109, can be used to adjust the width of the pulse if it is out of
specification.
A 10k NTC thermistor is required for charging, connected between TS and GND on J2 or the
“
on-board
”
10k resistor can be substituted by placing a shunt on JP1. Using both the external thermistor and internal
10k resistor may cause a hot temperature fault due to the low parallel resistance. No connection to the TS
pin will cause a cold temperature fault. During a temperature fault condition the OUT charge current is
disabled.
10k resistor may cause a hot temperature fault due to the low parallel resistance. No connection to the TS
pin will cause a cold temperature fault. During a temperature fault condition the OUT charge current is
disabled.
The EVM can interface with a micro-processor from your system that can be connected by removing the
JP3 shunt (disconnecting the EVM hardware producing the pulses) and applying the processor control
signal to JP3-1 (right pin) with the processor ground connected to the ground of the EVM. Note that when
JP3 is removed, the CTRL pin is pulled high by R6 and disables the IC. The micro-processor signal will
pull the CTRL pin low when not delivering the pulses, allowing proper operation.
JP3 shunt (disconnecting the EVM hardware producing the pulses) and applying the processor control
signal to JP3-1 (right pin) with the processor ground connected to the ground of the EVM. Note that when
JP3 is removed, the CTRL pin is pulled high by R6 and disables the IC. The micro-processor signal will
pull the CTRL pin low when not delivering the pulses, allowing proper operation.
The optional Battery Cell Replacement Circuit allows quick adjustment to the battery voltage. To check the
short circuit operation below 0.7V, the Cell P/S must be reduced to less than 1V. The programmed current
will have to be reduced so the OUT voltage can drop below 0.7V or the charge current will have to be
disabled and re-enabled.
short circuit operation below 0.7V, the Cell P/S must be reduced to less than 1V. The programmed current
will have to be reduced so the OUT voltage can drop below 0.7V or the charge current will have to be
disabled and re-enabled.
3
Performance Specification Summary
Specification
Test Conditions
MIN
TYP
MAX
UNIT
Input dc voltage, V
IN
Recommended input voltage range
5.1
5.5
V
Reduced performance, V
IN
(1)
Input voltage too low to maintain output regulation
3.75
10.2
V
(1)
As the input voltage drops near 5.1 VDC, the 4.9 V LDO may start to enter dropout.
As the input voltage drops near 3.75 V, the charge current may start to roll off.
Any input voltage near 10.2 V may put the device in OVP. See the data sheet for complete specifications.
As the input voltage drops near 3.75 V, the charge current may start to roll off.
Any input voltage near 10.2 V may put the device in OVP. See the data sheet for complete specifications.
2
1A, Single Cell LiFePO
4
Linear Battery Charger with 4.9 V, 50 mA LDO
SLVU473
–
May 2011
Copyright
©
2011, Texas Instruments Incorporated