Highly Integrated Battery Charger IC Use Case: Battery Backup Systems

Written by Glyn High Tech

December 15, 2020

Battery backup systems used in applications such as solar-powered outdoor cameras, lighting, and small cell systems like 4G/5G access points need multi-cell battery chargers for power. The traditional solution for multi-cell battery chargers is composed of several discrete power MOSFETs and multiple auxiliary components.

In traditional discrete solutions, designers need at least two power MOSFETs for the charger’s DC/DC converter, one power MOSFET to prevent battery power from flowing back to the input, and another MOSFET if power path functionality from the battery is needed. Control loops that include sensing circuits, compensating circuits, PWM generators, and drivers are essential. Furthermore, the system needs circuits that offer protection, indications for the input source or any changes in operating conditions, and other functions.

These discrete components result in a complicated design process, lack of flexible programmability, large board size, and high BOM costs.

The MP2759 is a highly integrated switching charger designed for charging applications with 1-cell to 6-cell series Li-ion, Li-polymer, and LiFePO4 battery packs. This IC integrates three power MOSFETs — plus programmable analog control circuits — into a 3mmx3mm package, and can operate reliably and safely with very few external components.

This fully integrated solution increases conversion efficiency, reduces time to market, and saves on design costs as it has the flexibility of 1 to 6 series cells (most solutions that can support up to 6 series cells are not integrated). This means designers can use same part and just change resistors connected to external pins program to accommodate different battery packs.

The MP2759 has the ability to program the input voltage regulation loop by setting an external resistor. When full sunlight is available from the solar panel, the charger IC regulates the max charge current and battery voltage as desired. However, if the IC detects a voltage drop on the panel due to reduced sunlight, it reduces the charge current accordingly to prevent the input voltage from collapsing further. This feature implements what is called maximum power point tracking (MPPT), where the MP2759 optimizes the maximum power being drawn from the solar panel under different lighting conditions without any additional circuitry. This allows the IC to achieve the fastest charging time, and keeps the backup battery fully charged for when the power source becomes too weak.

The MP2759 switches to battery power if the power supply goes away, and it supports up to 40V protection on the input, compared to only 28V in many other solutions.

Additional features include:

  • Programmable Input Current Limit Regulation
  • Programmable Battery Charging Temperature Range
  • Battery Thermal Monitor and Protection with JEITA Profile
  • Up to 36V Operation Input Voltage and 40V Protection
  • Up to 3A Programmable Charge Current
  • Up to 6 Cell Series with 3.6V/4.0V/4.1V/4.15V/4.2V/4.35V/4.4V Battery Regulation Voltage for Each Cell
  • Input Minimum Voltage Regulation for MPPT
  • Support OR Selection Power-Path Management to Allow Instant-On with a Low Battery
  • 0.5% Battery Regulation Voltage Accuracy
  • 450kHz or 700kHz Switching Frequency
  • Integrated Reverse Blocking FET and Buck Switching FETs
  • Internal Loop Compensation
  • Charge Operation Indicator
  • Input Status Indicator
  • Battery Over-Voltage Protection
  • Charging Safety Timer
  • Die Over-Temperature Protection

Interested? Email us at [email protected]

Information extracted from monolithicpower.com (link)

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