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LTC3443 Datasheet(PDF) 7 Page - Linear Technology |
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LTC3443 Datasheet(HTML) 7 Page - Linear Technology |
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7 / 16 page  LTC3443 7 3443fa OPERATIO The LTC3443 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on the VC pin de- termines the output duty cycle of the switches. Since the VC pin is a filtered signal, it provides rejection of frequen- cies from well below the switching frequency. The low RDS(ON), low gate charge synchronous switches provide high frequency pulse width modulation control at high efficiency. Schottky diodes across the synchronous switch D and synchronous switch B are not required, but provide a lower drop during the break-before-make time (typically 15ns). The addition of the Schottky diodes will improve peak efficiency by typically 1% to 2%. High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC’s quiescent current is a low 28 μA. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is factory trimmed to 600kHz. The oscillator can be synchronized with an external clock applied to the MODE/SYNC pin. A clock frequency of twice the desired switching frequency and with a pulse width of at least 100ns is applied. The oscillator sync range is 690kHz to 1.2MHz (1.38MHz to 2.4MHz sync frequency). Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier to obtain stability of the converter. The SHDN/SS pin will clamp the error amp output, VC, to provide a soft- start function. Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 4A typical. Before the switch current limit, the average current limit amp (3.2A typical) will source current into the FB pin to drop the output voltage. The current amplifier delay to output is typically 50ns. Reverse Current Limit The reverse current limit amplifier monitors the inductor current from the output through switch D. Once a negative inductor current exceeds – 400mA typical, the IC will shut off switch D. Output Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, VIN, VOUT and GND. Figure 2 shows the regions of operation for the LTC3443 as a function of the internal control voltage, VCI. The VCI voltage is a level shifted voltage from the output of the error amp (VC pin) (see Figure 5). The output switches are properly phased so the transfer between operation modes is continuous, filtered and transparent to the user. When VIN approaches VOUT the Buck/Boost region is reached where the conduction time of the four switch region is typically 150ns. Referring to Figures 1 and 2, the various regions of operation will now be described. Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. When the internal control voltage, VCI, is above voltage V1, output A begins to switch. During the off time of switch A, synchronous switch B turns on for the remainder of the time. Switches A and B will alternate |
Similar Part No. - LTC3443_15 |
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Similar Description - LTC3443_15 |
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