Autonomous Fast NiMH Battery Charger Using Single Chip IC

This simple Batteries charger circuit is designed for NiMH/NiCd batteries. It need no micro-controller nor any programming. Linear Technology Corporation produce the LTC4060, an autonomous 1- to 4-cell, 0.4A to 2A linear NiMH and NiCd battery charger complete controller. Here are the main features:

• No Sense Resistor or Blocking Diode Required
• Complete Fast Charger Controller for Single, 2-, 3- or 4-Series Cell NiMH/NiCd Batteries
• Automatic Detection of Battery
• Precharge for Heavily Discharged Batteries
• Optional Temperature Qualified Charging
• Charge and AC Present Status Outputs Can Drive LED
• Automatic Recharge Keeps Batteries Charged
• Programmable Fast Charge Current: 0.4A to 2A
• Accurate Charge Current: ±5% at 2A
• Fast Charge Current Programmable Beyond 2A with
  External Sense Resistor
• Manual Shutdown
• No Firmware or Microcontroller Required
• Termination by –?V, Maximum Voltage or Maximum Time
• Input Supply Range: 4.5V to 10V
• Available in 16-Lead DFN and TSSOP Packages
• Automatic Sleep Mode with Input Supply Removal
• Negligible Battery Drain in Sleep Mode: <1µA

The LTC4060 includes all the functions required to build a battery charger circuit, need no microcontroller or firmware. The LTC4060 eliminates the need for a sense resistor and blocking diode, which improve efficiency and the cost effectiveness. This IC chip is suitable for many application such as portable medical equipment, automotive diagnostic systems and industrial/telecommunication test devices.

The circuit schematic diagram shown in the figure above is an application that utilizes the optional battery temperature monitoring and optional externally programmable automatic recharge features. It also provides LEDs to indicate charging status and the presence of appropriate input supply voltage. The PROG pin is connected to a total resistance of 691 Ohm to ground that programs the fast-charge current at the PNP’s emitter to 2.02A (2A at the collector for beta of 100). The ARCT pin voltage is programmed to 1.25V. When the battery cell voltage falls below this low level threshold then an automatic recharge will begin. Optional capacitor CBAT is needed to filter out excessive contact bounces. To modify for charging a 4A-Hr battery at a C/2 rate, simply double the CTIMER capacitance. [Circuit’s schematic diagram source: Linear Technology LTC4060 Application Notes]