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UB6054AG-AG6-R Datasheet(PDF) 8 Page - Unisonic Technologies |
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UB6054AG-AG6-R Datasheet(HTML) 8 Page - Unisonic Technologies |
8 / 13 page UB6054A Preliminary CMOS IC UNISONICTECHNOLOGIESCO.,LTD 8 of 13 www.unisonic.com.tw QW-R502-926.b APPLICATION INFORMATION Stability Considerations The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is connected to the charger output. With no battery present, an output capacitor is recommended to reduce ripple voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1W resistor in series with the capacitor. No series resistor is needed if tantalum capacitors are used. In constant-current mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 20kΩ. However, additional capacitance on this node reduces the maximum allowed program resistor thus it should be avoided. Average, rather than instantaneous, charge current may be of interest to the user. For example, if a switching power supply operating in low current mode is connected in parallel with the battery, the average current being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses. In such a case, a simple RC filter can be used on the PROG pin to measure the average battery current as shown in Figure 1. A 10kΩ resistor has been added between the PROG pin and the filter capacitor to ensure stability. UTC UB6054A RPROG CFILTER GND PROG 10kΩ CHARGE CURRENT MONITOR CIRCUITRY Fig1. Isolating Capacitive Load on PROG Pin Thermal Limiting An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 120°C. This feature protects the UTC UB6054A from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the UTC UB6054A. The charge current can be set according to typical (not worst-case) ambient temperature with the assurance that the charger will automatically reduce the current in worst-case conditions. The conditions that cause the UTC UB6054A to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated by the internal MOSFET. This is calculated to be approximately: BAT BAT CC D I V V P Where PD is the power dissipated, VCC is the input supply voltage, VBAT is the battery voltage and IBAT is the charge current. The approximate ambient temperature at which the thermal feedback begins to protect the IC is: JA D A P C T 120 JA BAT BAT CC A I V V C T 120 Moreover, when thermal feedback reduces the charge current, the voltage at the PROG pin is also reduced proportionally as discussed in the Operation section. It is important to remember that UTC UB6054A applications do not need to be designed for worst-case thermal conditions since the IC will automatically reduce power dissipation when the junction temperature reaches approximately 120°C. |
Similar Part No. - UB6054AG-AG6-R |
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