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ISL9305IRTWCNLZ-T Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL9305IRTWCNLZ-T Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 16 page ISL9305 8 FN7605.2 February 9, 2015 Submit Document Feedback Soft-Start The soft-start reduces the in-rush current during the start-up stage. The soft-start block limits the current rising speed so that the output voltage rises in a controlled fashion. Overcurrent Protection The overcurrent protection for DCD1 and DCD2 is provided on ISL9305 for when an overload condition occurs. When the current at P-Channel MOSFET is sensed to reach the current limit, the internal protection circuit is triggered to turn off the P-Channel MOSFET immediately. DCD Short-Circuit Protection The ISL9305 provides Short-Circuit Protection for both DCD1 and DCD2. The feedback voltage is monitored for output short-circuit protection. When the output voltage is sensed to be lower than a certain threshold, the internal circuit will change the PWM oscillator frequency to a lower frequencies in order to protect the IC from damage. The P-Channel MOSFET peak current limit remains active during this state. Undervoltage Lock-out (UVLO) An undervoltage lock-out (UVLO) circuit is provided on ISL9305. The UVLO circuit block can prevent abnormal operation in the event that the supply voltage is too low to guarantee proper operation. The UVLO on VINDCD1 is set for a typical 2.2V with 100mV hysteresis. VINLDO1 and VINLDO2 are set for a typical 1.4V with 50mV hysteresis. When the input voltage is sensed to be lower than the UVLO threshold, the related channel is disabled. DCDPG (DCD Power-Good) ISL9305 offers an open-drain Power-Good signal with programmable delay time for monitoring the converters DCD1 and DCD2 output voltages status. When both DCD1 and DCD2 are enabled and their output voltages are within the power-good window, an internal power-good signal is issued to turn off the open-drain MOSFET so the DCDPG pin voltage can be externally pulled high after a programmed delay time. If either DCD1 or DCD2 output voltages or both of them are not within the power-good window, the DCDPG outputs an open-drain logic low signal after the programmed delay time. When there is only one DCD converter (either DCD1 or DCD2) is enabled, then the DCDPG only indicates the status of this active DCD converter. For example, if only DCD1 converter is enabled and DCD2 converter is disabled, when DCD1 output is within the power-good window, internal power-good signal will be issued to turn off the open-drain MOSFET so the DCDPG pin voltage is externally pulled high after the programmed delay time. If output voltage of DCD1 is outside the power-good window, the DCDPG outputs an open-drain logic low signal after the programmed delay time. It is similar when only DCD2 is enabled and DCD1 is disabled. When both converters are disabled, DCDPG always outputs the open-drain logic low signal. Low Dropout Operation Both DCD1 and DCD2 converters feature the low dropout operation to maximize the battery life. When the input voltage drops to a level that the converter can no longer operate under switching regulation to maintain the output voltage, the P-Channel MOSFET is completely turned on (100% duty cycle). The dropout voltage under such a condition is the product of the load current and the ON-resistance of the P-Channel MOSFET. Minimum required input voltage VIN under such condition is the sum of output voltage plus the voltage drop across the inductor and the P-Channel MOSFET switch. Active Output Voltage Discharge For DCD1/DCD2 The ISL9305 offers a feature to actively discharge the output voltage of DCD1 and DCD2 via an internal bleeding resistor (typical 115Ω) when the channel is disabled. This feature is enabled by default, thus outputs can be disabled individually through programming the control bit in DCD_PARAMETER register. Thermal Shutdown The ISL9305 provides built-in thermal protection function with thermal shutdown threshold temperature set at +155°C with +25°C hysteresis (typical). When the die temperature is sensed to reach +155°C, the regulator is completely shut down and as the temperature is sensed to drop to +130°C (typical), the device resumes normal operation starting from the soft-start. Board Layout Recommendations The ISL9305 is a high frequency switching charger and hence the PCB layout is a very important design practice to ensure a satisfactory performance. The power loop is composed of the output inductor L, the output capacitor COUT, the SW pin and the PGND pin. It is important to make the power loop as small as possible and the connecting traces among them should be direct, short and wide; the same practice should be applied to the connection of the VIN pin, the input capacitor CIN and PGND. The switching node of the converter, the SW pin, and the traces connected to this node are very noisy, so keep the voltage feedback trace and other noise sensitive traces away from these noisy traces. The input capacitor should be placed as close as possible to the VIN pin. The ground of the input and output capacitors should be connected as close as possible as well. In addition, a solid ground plane is helpful for a good EMI performance. The ISL9305 employs a thermal enhanced TQFN package with an exposed pad. The exposed pad should be properly soldered on thermal pad of the board in order to remove heat from the IC. The thermal pad should be big enough for 9 vias as shown in Figure 4. FIGURE 4. EXPOSED THERMAL PAD |
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