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RT9619 Datasheet(PDF) 10 Page - Richtek Technology Corporation |
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RT9619 Datasheet(HTML) 10 Page - Richtek Technology Corporation |
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10 / 12 page  RT9619/A 10 DS9619/A-04 March 2007 www.richtek.com Please note that the VCC trigger point to RT9619/A is at 3V, and the clamped level on PHASE pin is at about 2.4V. Obviously since the PHASE pin voltage increases during initial start-up, the VCORE increases correspondingly, but it would quickly drop-off followed by LGATE and VCC decreased. Layout Consideration Figure 6 shows the schematic circuit of a two-phase synchronous buck converter to implement the RT9619/A. The converter operates from 5V to 12V of VIN. Figure 5. Waveforms at High Side MOSFET Shorted VCC VIN PGND BOOT UGATE PHASE LGATE RT9619/A 1uF C L 3nF 20 C U 3nF 2N7002 2N7002 +12V +12V 1uF PWM 1N4148 C BOOT 10 VCC PHASE LGATE VCORE (2V/Div) (2V/Div) (2V/Div) (2V/Div) Time (50ms/Div) 0 100 200 300 400 500 600 700 800 900 1000 0 200 400 600 800 1000 Frequency (kHz) CU=CL=3nF CU=CL=1nF CU=CL=2nF Power Dissipation vs. Frequency The operating junction temperature can be calculated from the power dissipation curves (Figure 4). Assume VCC=12V, operating frequency is 200kHz and the CU=CL=1nF which emulate the input capacitances of the high side and low side power MOSFETs. From Figure 4, the power dissipation is 100mW. For RT9619/A, the package thermal resistance θJA is 160°C/W, the operating junction temperature is calculated as : Figure 3. Test Circuit This dissipation is a function of switching frequency and total gate charge of the selected MOSFET. Figure 3 shows the power dissipation test circuit. CL and CU are the UGATE and LGATE load capacitors, respectively. The bootstrap capacitor value is 1 μF. Figure 4 shows the power dissipation of the RT9619/A as a function of frequency and load capacitance. The value of the CU and CL are the same and the frequency is varied from 100kHz to 1MHz. Figure 4. Power Dissipation vs. Frequency TJ = (160 °C/W x 100mW) + 25°C = 41°C (11) where the ambient temperature is 25 °C. The method to improve the thermal transfer is to increase the PCB copper area around the RT9619/A first. Then, adding a ground pad under IC to transfer the heat to the peripheral of the board. Over-Voltage Protection Function at Power-On An unique feature of the RT9619/A driver is the addition of over-voltage protection in the event of upper MOSFET direct shorted before power-on. The RT9619/Adetects the fault condition during initial start-up, the internal power-on OVP sense circuitry will rapidly drive the output lower MOSFET on before the multi-phase PWM controller takes control. Figure 5 shows the measured waveforms with the high side MOSFET directly shorted to 12V. |
Similar Part No. - RT9619 |
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Similar Description - RT9619 |
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