AN-1164

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Charge Current

The charge settings for LM3647 current control are shown below. If the external LM317 is used to control the charge current then the jumpers J9, J10 and J13 have no relevance, when using LM317 regulation mode, this jumper must be placed in either position. If external (LM317) regulation is used then set jumper J7 to position ²slow²; for LM3647 regulation set J7 to ²fast².

LM3647 Current Regulation

The I jumper J10 is used to select between different current sense resistors. The values available are 0.047W and 0.100W.

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The charge current is set with jumpers J9 and J13. The figure shows two possible currents that depend on how jumper J10 is set. The higher current is selected when J10 is set to 0.047W and the lower current is selected when J10 is set to 0.100W.

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1.0FUNCTIONAL DESCRIPTION

1.1General

The LM3647 has voltage and current sensing inputs that are used to control a PWM-output. The voltage input is connected to the battery via a resistor divider network, and the current input is connected to an operational amplifier that amplifies the voltage across a current sense resistor located at the positive battery terminal. The PWM-output can be configured as a high speed PWM, or as a low speed (ON/OFF) output for an external current regulator. The latter is for low cost Ni-Cd/Ni-MH charger applications, eliminating the need for any operational amplifiers or current feedback circuitry.

The high speed PWM is filtered to a DC-level and fed into an operational amplifier that controls a power-NPN transistor. The LM3467 requires charge current feedback to control the charge current.

1.2 Modes of Operation

1.2.1 Charging Ni-Cd/Ni-MH Batteries

The charger detects that a battery is connected when the CEL-pin > 1.0V. The charger can also detect a battery that has been deeply discharged and does not have any voltage across the battery terminals. This is accomplished by applying a small 'pre-charge' current once every minute for up to 15 seconds. The deeply discharged battery will accept this charge and the battery potential will eventually rise above the 1.0V limit to initiate normal charging. When the charger has detected a battery (CEL-pin > 1.0V), it checks to see if the temperature is within range to start charging. If it is, then it applies a small current of 0.2C for approximately 5 minutes. If the battery voltage exceeds the maximum battery voltage (CEL-pin > 3.017V), the LM3647 stops charging and stays in error mode until the battery is removed. If the battery voltage has not risen above the bad battery threshold (CEL-pin < 1.2V), then the battery is considered to be defective and the charger goes into error mode. If the battery passes all tests, then after the five minutes have passed, the charger starts the next phase: Fast Charge.

During Fast Charge, the charger applies a constant current to the battery and monitors both battery voltage and temperature. The charger is looking for a drop in the battery voltage that normally occurs at the end of the Fast Charge cycle. The size of the voltage drop differs depending on battery type (Ni-Cd/Ni-MH). For Ni-Cd it's approximately 50 mV/cell and for Ni-MH it's approximately 17 mV/cell. If the temperature rise is larger than 50 mV/minute (~1ÊC/minute) when charging Ni-MH batteries, the battery has reached the end of the Fast Charge cycle.

During charging the temperature-input is constantly measured to ensure that the battery's temperature is within proper range. If the temperature is out of range the charger aborts the charge and goes into error mode.

During the next charge phase (Topping Charge) the LM3647 applies a small current of 0.2C for a time set by the time-selection RC-network (see section below). This phase may be followed by a Maintenance Charge phase, depending on selection-pins.

1.2.2 Charging Li-Ion Batteries

The charger detects that a battery is connected when the CEL-pin > 1.0V. The charger can also detect a battery that has been deeply discharged and does not have any voltage across the battery terminals. This is accomplished by applying a small 'pre-charge' current once every minute for up to 15 seconds. The deeply discharged battery will accept this charge and the battery potential will eventually rise above the 1.0V limit to initiate normal charging. When the charger has detected a battery (CEL-pin > 1.0V), it checks to see if the temperature is within range to start charging. If it is, then it applies a small current of 0.2C for approximately 1 minute. If the battery voltage is close to fully charged, the charger will not reach the charging voltage within 1 minute,

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National Instruments LM3647 user manual Functional Description
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LM3647 specifications

The National Instruments LM3647 is a versatile and advanced power management integrated circuit designed specifically for applications in mobile and portable devices. This device provides an efficient power supply solution that caters to the demands of today's sophisticated electronics.

One of the main features of the LM3647 is its ability to deliver a highly accurate output voltage. With a low output voltage ripple, it ensures that sensitive components receive stable power, thereby enhancing the performance and reliability of the system. The device typically uses a constant on-time control scheme, which allows for rapid transient response and improves overall efficiency, especially during dynamic load changes common in portable devices.

The LM3647 offers an impressive input voltage range, typically from 2.5V to 5.5V, making it compatible with a wide range of power sources, including lithium-ion batteries and USB power. Additionally, the device is highly efficient, boasting peak efficiencies of over 95%. This efficiency translates to extended battery life, a crucial factor for portable electronics.

Another significant characteristic of the LM3647 is its integrated power path management capability. This feature allows it to intelligently manage power distribution between the battery and the load, ensuring seamless transitions between battery and wall power, and providing system protection from overloads and short circuits.

The LM3647 also supports a flexible output configuration, featuring multiple outputs that can be independently programmed. This flexibility is particularly beneficial in applications such as smartphones, tablets, and wearables that require multiple voltage rails for various components, including processors, displays, and sensors.

Moreover, the LM3647 incorporates advanced thermal management techniques. With a package designed to dissipate heat efficiently, it helps maintain operational stability and longevity of the device even under heavy load conditions.

In summary, the National Instruments LM3647 stands out as a high-performance power management IC leveraging cutting-edge technologies to provide efficient power solutions for mobile and portable devices. Its features, including high efficiency, accurate output voltage, integrated power path management, and flexible output configurations, combined with robust thermal characteristics, make it an excellent choice for designers aiming for optimal power management in their electronic devices.
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