National Instruments LM3647 user manual Phase Timeout, Setting The Charge Current

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The actual timeouts (with RCIN @ 2.5 MHz) is:

Phase

Timeout

 

 

Fast Charge

∼ 330 Minutes

 

 

Topping Charge

∼ 80 Minutes

 

 

EXAMPLE 2:

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The actual timeouts (with RCIN @ 2.5 MHz) is:

Phase

Timeout

 

 

Fast Charge Constant Current

− 130 Minutes

 

 

Topping Charge Constant Voltage

− 190 Minutes

 

 

1.2.2.4 Setting The Charge Current

The charge-current is selected by setting the current sensing resistor and the gain of the differential amplification stage. The current sensing resistor (R5) should be dimensioned such that the voltage drop over it is not too small, since the signal will be more susceptible to noise and offsets in the amplification-stage. The resistance should not be too large either (especially in high-current applications), because this will only generate more heat from the component. A suitable value is one where 50 mV dropped across the resistor when maximum current flows through it. The differential signal is then amplified, inverted and centered around the 2.5V reference by the operational amplifier and fed to the CS pin on the LM3647. The gain must be dimensioned by setting the appropriate ratio between R1 (R2) and R3 (R4). The figure below is dimensioned for a maximum current of about 1.1A. This was dimensioned using the following formula:

1.2.2.5 Setting Maximum Battery Voltage

The resistor network (see the figure below) scales the battery voltage to a suitable level for the LM3647. For Ni-Cd/Ni-MH batteries the network is less critical, but limits the maximum battery voltage, it is only used as a backup termination method. For Li-Ion batteries the network must be more accurate, requiring precision resistors with low tolerances.

·For Ni-Cd/Ni-MH:

The dimensioning is accomplished in the following manner:

First calculate the maximum battery voltage for the specific battery pack. See example below.

BatteryVoltage/Cell = 1.2V NumberOfCells = 5 → Battery-

PackVoltage = 1.2x5 = 6V

MaximumBatteryVoltage/Cell = 1.85V → MaximumBattery-

Voltage = 1.85x5 = 9.25V

When the Maximum Battery Voltage has been determined, the voltage divider network has to be dimensioned using the following formula:

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Contents KEY Features Jumper SettingsGeneral Description Documentation InformationFunctional Description Clarifications Regarding Circuit Schematics Setting The Charge TimeoutComponents Critical to Total Charger Performance MinutesSetting The Charge Current Phase TimeoutSetting Maximum Battery Voltage Charge Phase Duty Cycle Application Information Typical Example Ni-Cd/Ni-MHSet To SEL1 SEL2 SEL3Li-Ion LM3647 Reference Design DEMO-BOARD Life Support Policy

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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