Datasheet LTC3415 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | 7A, PolyPhase Synchronous Step-Down Regulator |
| Páginas / Página | 28 / 9 — OPERATION Short-Circuit Protection. Multiphase Operation. Output … |
| Formato / tamaño de archivo | PDF / 322 Kb |
| Idioma del documento | Inglés |
OPERATION Short-Circuit Protection. Multiphase Operation. Output Overvoltage. Figure 2a. 2-Phase Operation
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LTC3415
OPERATION Short-Circuit Protection
overvoltage comparator during the time the LTC3415’s When the output is shorted to ground, the LTC3415 internal reference is powering up. As a result, the bottom will drop cycles to allow the inductor time to decay and switch turns on until the amount of reverse current trips prevent the current from running away. Under this fault the INEGLIM comparator threshold. condition, the top P-channel power MOSFET turns on for
Multiphase Operation
a minimum on-time and is held off for as long as it takes for the inductor current to decay to a safe level. For output loads that demand more than 7A of current, multiple LTC3415s can be cascaded to run out of phase to
Output Overvoltage
provide more output current without increasing input and If the LTC3415’s output voltage exceeds the regulation output voltage ripple. The CLKIN pin allows the LTC3415 point by 10%, which is refl ected as a V to synchronize to an external clock (between 0.75MHz and FB voltage of 0.66V or above, the LTC3415 will attempt to bring back to regu- 2.25MHz) and the internal phase-locked-loop allows the lation by shutting off the top P-channel power MOSFET LTC3415 to lock onto CLKIN’s phase as well. The CLKOUT and turning on the bottom N-Channel power MOSFET for signal can be connected to the CLKIN pin of the following as long as needed to lower V LTC3415 stage to line up both the frequency and the phase OUT. However, if the reverse current fl owing from V of the entire system. Tying the PHMODE pin to SV OUT back through the bottom IN, SGND, N-Channel power MOSFET to PGND is greater than 7A, or SVIN/2 generates a phase difference (between CLKIN the INEGLIM comparator trips and shuts off the bottom and CLKOUT) of 180 degrees, 120 degrees, or 90 degrees N-Channel power MOSFET to protect it from being de- respectively, which corresponds to 2-phase, 3-phase, or stroyed. This scenario can happen when the LTC3415 tries 4-phase operation. A total of 12 phases can be cascaded to start into a pre-charged load, which could trigger the to run simultaneously out of phase with respect to each 0 180 +120 +120 CLKIN CLKOUT CLKIN CLKOUT S PHMODE S VIN VIN PHMODE PHASE 1 PHASE 2 3415 F02a
Figure 2a. 2-Phase Operation
0 120 240 +120 +120 CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT PHMODE PHMODE PHMODE PHASE 1 PHASE 2 PHASE 3 3415 F02b
Figure 2b. 3-Phase Operation
0 90 180 270 +90 +90 +90 CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT SVIN SV SV SV PHMODE IN PHMODE IN PHMODE IN PHMODE 2 2 2 2 PHASE 1 PHASE 2 PHASE 3 PHASE 4 3415 F02c
Figure 2c. 4-Phase Operation
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OPERATION Short-Circuit Protection
overvoltage comparator during the time the LTC3415’s When the output is shorted to ground, the LTC3415 internal reference is powering up. As a result, the bottom will drop cycles to allow the inductor time to decay and switch turns on until the amount of reverse current trips prevent the current from running away. Under this fault the INEGLIM comparator threshold. condition, the top P-channel power MOSFET turns on for
Multiphase Operation
a minimum on-time and is held off for as long as it takes for the inductor current to decay to a safe level. For output loads that demand more than 7A of current, multiple LTC3415s can be cascaded to run out of phase to
Output Overvoltage
provide more output current without increasing input and If the LTC3415’s output voltage exceeds the regulation output voltage ripple. The CLKIN pin allows the LTC3415 point by 10%, which is refl ected as a V to synchronize to an external clock (between 0.75MHz and FB voltage of 0.66V or above, the LTC3415 will attempt to bring back to regu- 2.25MHz) and the internal phase-locked-loop allows the lation by shutting off the top P-channel power MOSFET LTC3415 to lock onto CLKIN’s phase as well. The CLKOUT and turning on the bottom N-Channel power MOSFET for signal can be connected to the CLKIN pin of the following as long as needed to lower V LTC3415 stage to line up both the frequency and the phase OUT. However, if the reverse current fl owing from V of the entire system. Tying the PHMODE pin to SV OUT back through the bottom IN, SGND, N-Channel power MOSFET to PGND is greater than 7A, or SVIN/2 generates a phase difference (between CLKIN the INEGLIM comparator trips and shuts off the bottom and CLKOUT) of 180 degrees, 120 degrees, or 90 degrees N-Channel power MOSFET to protect it from being de- respectively, which corresponds to 2-phase, 3-phase, or stroyed. This scenario can happen when the LTC3415 tries 4-phase operation. A total of 12 phases can be cascaded to start into a pre-charged load, which could trigger the to run simultaneously out of phase with respect to each 0 180 +120 +120 CLKIN CLKOUT CLKIN CLKOUT S PHMODE S VIN VIN PHMODE PHASE 1 PHASE 2 3415 F02a
Figure 2a. 2-Phase Operation
0 120 240 +120 +120 CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT PHMODE PHMODE PHMODE PHASE 1 PHASE 2 PHASE 3 3415 F02b
Figure 2b. 3-Phase Operation
0 90 180 270 +90 +90 +90 CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT CLKIN CLKOUT SVIN SV SV SV PHMODE IN PHMODE IN PHMODE IN PHMODE 2 2 2 2 PHASE 1 PHASE 2 PHASE 3 PHASE 4 3415 F02c
Figure 2c. 4-Phase Operation
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