Features and Benefits
- Step-Up Backup Supply and Step-Down Battery Charger
- 6.5A Switches for 2.5A Backup from 3.2V Battery
- Input Current Limit Prioritizes Load Over Charge Current
- Input Disconnect Switch Isolates Input During Backup
- Automatic Seamless Switch-Over to Backup Mode
- Input Power Loss Indicator
- System Power Loss Indicator
- Pin Selectable Battery: Li-Ion (3.95V/4.0V/4.05V/4.1V) or LiFePO4 (3.45V/3.5V/3.55V/3.6V)
- Optional OVP Circuitry Protects Device to >60V
- Constant Frequency Operation
- Low Profile (0.75mm) 24-Lead 4mm × 5mm QFN Package
The LTC4040 is a complete 3.5V to 5.5V supply rail battery backup system. It contains a high current step-up DC/DC regulator to back up the supply from a single-cell Li-Ion or LiFePO4 battery. When external power is available, the step-up regulator operates in reverse as a step-down battery charger.
The LTC4040’s adjustable input current limit function reduces charge current to protect the main supply from overload while an external disconnect switch isolates the external supply during backup. When the input supply drops below the adjustable PFI threshold, the 2.5A boost regulator delivers power from the battery to the system output.
An optional input overvoltage protection (OVP) circuit protects the LTC4040 from high voltage damage at the VIN pin. One logic input selects either the Li-Ion or the LiFePO4 battery option, and two other logic inputs program the battery charge voltage to one of four levels suitable for backup applications. The LTC4040 is available in a low profile (0.75mm) 24-Lead 4mm × 5mm QFN package.
- Fleet and Asset Tracking
- Automotive GPS Data Loggers
- Automotive Telematics Systems
- Toll Collection Systems
- Security Systems
- USB Powered Devices
Product Lifecycle Recommended for New Designs
This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.
Evaluation Kits (2)
Demonstration circuit 2118B is a combination step-down battery charger and step-up battery backup regulator using the LTC4040 monolithic system power manager. The DC2118B has an input voltage range from 4.8V to 5.5V with overvoltage protection (OVP) to 40V, as limited by the external MOSFET. The input current is monitored to prioritize the load up to the 2.5A threshold before charge current is reduced.
As initially configured, DC2118B is programmed for 2A charge current limit when in charge mode. The charge voltage is jumper-selectable in 8 discrete steps from 3.45V to 3.6V for LiFePO4 chemistry or 3.95V to 4.1V for Li-ion chemistry, according to the F2/F1/F0 programming input settings.
The charge current limit is adjustable via the PROG pin resistor. End-of-charge status is triggered by current falling below C/8 and indicated by the CHRG LED. The optional NTC input provides temperature fault detection and status indicated by the FAULT LED. Charging can be enabled/disabled with the ENCHG jumper.
Following an input power failure, the circuit automatically shifts to battery backup boost mode to regulate the VSYS output rail. The backup mode system output voltage is initially programmed for 5V. The input power failure status is indicated by the PFO LED.
If VSYS ever falls below the programmed reset threshold voltage, the RST LED will change states to indicate the need to reset the system and recharge the battery. Backup regulation can be enabled/disabled with the ENBST jumper.
For convenience, all LEDs can be disabled with the LED jumper to reduce the quiescent current of the system.
This evaluation board is obsolete and no longer recommended.
Demonstration circuit 2118A is a combination step-down battery charger and step-up battery backup regulator using the LTC4040 monolithic system power manager. The DC2118A has an input voltage range from 4.8V to 5.5V with overvoltage protection (OVP) to 40V, as limited by the external MOSFET. The input current is monitored to prioritize the load up to the 2.5A threshold before charge current is reduced.
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