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NiMH NiCd battery charger using LTC4011

Using the LTC4011 integrated circuit you can design a very simple and high efficiency nickel battery fast charger . The LTC4011 provide a complete solution in a small package using few external components. A 550kHz PWM current source controller and all necessary charge initiation, monitoring and termination control circuitry are included.
Design for this NiMH NiCd batteries charger is very simple and can be used for multiple applications like : standalone battery charger , portable instruments , or back-up battery management .
The LTC4011 automatically senses the presence of a DC adapter and battery insertion or removal. Heavily discharged batteries are precharged with a trickle current.
Charge current is programmed using the following equation: Rsense=100mV/Iprog .
RSENSE is an external resistor connected between the SENSE and BAT pins .
The maximum fast charge period is determined by the following equation:
Rtimer(ohms)=tmax(hours)/30x10^-6
The opencircuit voltage of the DC source should be between 4.5V and 34V, depending on the number of cells being charged.

The following equation can be used to determine the minimum full-load voltage that should be provided by the external DC power source : DCIN(MIN) = (n • 2V) + 0.3V , where n is the number of series cells in the battery pack.

This nickel NiMH NiCd batteries charger electronic project is a full-featured 2A charger project that allows maximum input voltage range from the DC adapter. The inherent voltage ratings of the VCELL, VCDIV, SENSE and BAT pins allow charging from one to sixteen series nickel cells in this application, governed only by the VCC overhead limits previously discussed.
This charger includes all average cell voltage and battery temperature sensing circuitry required for the LTC4011 to utilize its full range of charge qualification, safety monitoring and fast charge termination features.

A green LED indicates valid DC input voltage and installed battery, while a pair of red LEDs indicates charging. A yellow LED indicates fault conditions.
NiMH NiCd battery charger circuit design using LTC4011

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Comments

The LTC4011 has several features (e.g., programmable cell count, precharge, multiple charge termination methods, automatic recharge) that makes it very attractive for products that may be operated in either a freestanding portable mode, or connected to a power source. It is ESSENTIAL to have a solid electrical connection from the underside thermal pad (shown as "Pin 21" in the data sheet) to system ground. Without this connection the IC can fail catastrophically as soon as power is applied. This electrical connection is required even in non-demanding applications where thermal analysis shows no need for heat transfer to the PCB, or external heat sinks. Note that the pad layout shown on page 24 of the data sheet can NOT be used for a hand-soldered prototype and may be problematical even with reflow soldering. As a minimum, the PCB "pad 21" should extend beyond both ends of the package body, and plated-through vias in the thermal pad provide a visual indication that solder has flowed uniformly across the thermal pad.

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