Phase Timeout | National Instruments LM3647 guide

AN-1164

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

Phase	Timeout

Fast Charge	∼ 330 Minutes

Topping Charge	∼ 80 Minutes

EXAMPLE 2:

AN101315-19

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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